The role of the absence of Hyrtl’s anastomosis in monochorionic pregnancy: friend or foe?

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Liu Ziling, Ruan Jie This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2366222/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background: Hyrtl’s anastomosis, an intra-arterial shunt, plays a protective role when the placental territories supplied by the umbilical arteries are different in size. Its absence is associated with an increased risk of poor outcomes in singleton pregnancy. However, the literature and studies on the effect of absent Hyrtl’s anastomosis in twin placentas are rare. Case Presentation: We present a case of a monochorionic diamniotic(MCDA) twin pregnancy complicated with type I selective fetal growth restriction(SFGR). Despite discordance in placental territory and cord insertion sites, the patient had an overall good pregnancy process, suggesting that the absence of Hyrtl’s anastomosis may have played a benign role. Conclusions: The absence of Hyrtl’s anastomosis in our case seemed to show a favorable effect, representing a finding of opposite effects in monochorionic placentas compared with singleton placentas. Hyrtl’s anastomosis monochorionic diamniotic twin pregnancy selective fetal growth restriction placental territory discordance Figures Figure 1 Figure 2 Background Hyrtl’s anastomosis, an intra-arterial shunt, is present in approximately 96% of umbilical cords between the umbilical arteries, is usually 1.5-2cm long and positioned within 3 cm of the placental cord insertion [ 1 ]. From the limited studies of singleton placentas, the presence of Hyrtl’s anastomosis plays a protective role when the placental territories supplied by the umbilical arteries are different in size[ 2 ]. It equalizes pressures between the two umbilical arteries before entering the placenta and functions as a safety valve in the event of placental compression or umbilical artery blockage[ 1 ].In placentas lacking a Hyrtl’s anastomosis, the two umbilical arteries supplied a similar area, indicating a relatively high degree of symmetry[ 3 ]. However, the literature and studies on Hyrtl’s anastomosis in twin placentas are scarce. Here, we reported a monochorionic diamniotic twin pregnancy complicated with type I selective fetal growth restriction. Despite discordance in placental territory and cord insertion sites, the patient had an overall good pregnancy process, suggesting that the absence of Hyrtl’s anastomosis may have played a benign role. Case Presentation A 29-year-old woman, gravida 4 para 0, spontaneously conceived. Ultrasound examination at 12 weeks gestation confirmed MCDA twin pregnancy. The patient was referred to our obstetrics unit at 24 + 5 weeks of gestation because of suspected fetal complex congenital heart disease(CHD). Ultrasound in our hospital suggests aortic coarctation associated with ventricular septal defect in one of the twins. At the first visit, the estimated fetal weight (EFW) of the CHD fetus fell below the 3rd percentile, and discordance between the EFW of the two fetuses was 9.4%. Therefore, type I SFGR was also diagnosed. Doppler studies of both twins as well as fetal viability were routinely performed at roughly two-weeks interval. Serial ultrasound monitoring showed normal fetal growth velocity(see in Table.1 and Figure.1), amniotic volume, umbilical artery (UA) Doppler, ductus venosus (DV) Doppler, and middle cerebral artery (MCA) Doppler in both fetuses. No significant chromosomal abnormalities in either fetus were detected by chromosome microarray analysis. The patient chose to continue the pregnancy and refused to undergo elective feticide after multidisciplinary consultation with the pediatric cardiovascular physician, neonatologist, and medical geneticist. The patient was admitted at 30 weeks of gestation for threatened preterm labor and treated with dexamethasone and magnesium sulfate, and discharged at 30 + 4 weeks after inhibition of uterine contractions. At 35 + 3 weeks` gestation, she was readmitted for cervical dilation and underwent an emergency cesarean section. The birth weight of twin female neonates was 2110/2000g (birthweight discordance ratio was 5.2%), and the 1-minute Apgar score was 10. The smaller fetus was immediately transferred to the neonatal intensive care unit and underwent single-stage surgical repair 14 days after birth. Placental perfusion staining suggests the placental territory discordance ratio was 64.2% (calculated by Image J software processing) with velamentous cord insertion of the smaller/CHD fetus. The smaller fetus had a placental area of only 13×9 cm with an islet-like succenturiate placenta of 3×2cm. Rarely, we found a lack of Hyrtl's anastomosis between 2 umbilical arteries in the larger fetus (see in Figure.2). To make comparisons, we also reviewed more than 50 cases of monochorionic placenta stained by perfusion from Dec.2021 to Aug. 2022 in our hospital and found that a total of 9 cases had placental territory discordance ratio greater than 50% (for more information on the images see Supplementary Files). The remaining 8 patients, except the present case, all presented with type Ⅱ-Ⅲ SFGR. Placental abruption and the smaller fetal demise occurred in one case. Considering the poor prognosis of the larger surviving fetus, the patients demand lethal induction of labor. The average gestational age at delivery for the other 7 cases was 31 + 6 weeks, and the average birthweight discordance ratio was 36.2%. Discussion And Conclusions In early gestation, multiple anastomoses occur between the umbilical arteries but are subsequently reduced to one connection within the first 3 cm of cord proximal to the chorionic plate, that is, Hyrtl’s anastomosis. It was first noted by the descriptive anatomist Joseph Hyrtl, in 1870. The positive effect of this anastomosis in the singleton placentas has been reported in previous researches. The main function is to balance the pressure and flow in the two umbilical arteries helping to equalize the area of placental vascular territories. Raio[ 2 ] reported a series of antenatal functional evaluations of this anastomosis in 41 women. The difference between the resistance indices of the two umbilical arteries was higher after than before the anastomosis. In Byrne’s models[ 4 ], placentas with an anastomosis present showed relatively small discordance between blood pressures feeding each lobe compared with larger differences predicted when an anastomosis was not included. Therefore, Hyrtl's anastomosis plays a favorable role in equalizing blood pressures between the placental lobes fed by each UA in singleton placentas, especially in the context of compensatory prevention of potential fetal compromise due to placental insufficiency and its absence is associated with an increased risk of poor outcomes. Studies on Hyrtl’s anastomosis of twin placentas, especially monochorionic placentas, are rare. We finally found only one paper on this anastomosis. However, the opposite result compared to the singleton placenta was obtained. Walker]5] reported a case of monochorionic twin pregnancy associated with SFGR and suspected twin-twin transfusion syndrome(TTTS). Reversed end-diastolic flow(REDF), which is an immediate precursor of fetal demise, was noted at multiple sites in the umbilical cord of the smaller/donor twin on the day of hospital admission. Fortunately, the case had a prolonged fetal survival period of 2 weeks before delivery. Pathologic examination of the placenta after delivery disclosed an unbalanced vascular communication between the twins and the absence of Hyrtl’s anastomosis in the smaller/donor twin. The authors believe the absent Hyrtl’s anastomosis can allow adequate fetal oxygenation via the flow through one umbilical artery despite persistent REDF in the other, and allow for the relative independence of interfetal vascular anastomoses to better offset adverse effects of the twin-to-twin transfusion syndrome. The absence of Hyrtl’s anastomosis in our case also seemed to show a favorable effect similar to this literature above. However, the difference is that the absent Hyrtl’s anastomosis appears in the larger twin, not the smaller twin. In comparison to the other monochorionic placentas with large placental territory discordance, the growth difference between the twins in this case gradually decreased with increasing gestational weeks and consistently maintained good umbilical blood perfusion. The possible reason is that the two umbilical arteries of the larger fetus do not interfere with each other. Branches of one umbilical artery coincide with the smaller fetus to compensate for the relatively small placental volume, and the other umbilical artery is independent to ensure adequate cotyledonary perfusion and adequate fetal oxygenation of the larger fetus. The absence of an equalizing anastomosis allows two relatively separate and independent placental circulations. Thus, it is like transforming the placenta into an intermediate state between dichorionic and monochorionic. In conclusion, this case represents a finding of opposite effects of Hyrtl’s anastomosis in monochorionic placentas compared with singleton placentas. More cases of placental perfusion staining are needed to support our view. Abbreviations MCDA: monochorionic diamniotic SFGR: selective fetal growth restriction CHD: congenital heart disease EFW: estimated fetal weight UA: umbilical artery DV: ductus venosus MCA: middle cerebral artery TTTS: twin-twin transfusion syndrome REDF: Reversed end-diastolic flow GA: gestational age Declarations Ethics approval and consent to participate: Published case report comply with the guidelines for human studies and was conducted ethically in accordance with the World Medical Association Declaration of Helsinki. Written informed consent was obtained from the patient for publication of this case report and any accompanying images. Consent for publication: Written informed consent was obtained from the patient for publication of this case report and any accompanying images. Availability of data and materials: The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request. Competing interests: None declared. Funding: Not applicable. Authors' contributions: LZ participated in the writing, and organization of the manuscript. RJ took charge in patient consultation and placental perfusion, and coordinated revising of the manuscript. All authors listed have read and approved the fnal version of the manuscript. Acknowledgements: Not applicable. References Sherer DM, Al-Haddad S, Cheng R, Dalloul M. Current Perspectives of Prenatal Sonography of Umbilical Cord Morphology. Int J Womens Health. 2021;13:939-71. http://doi.org/10.2147/IJWH.S278747. Raio L, Ghezzi F, di Naro E, Franchi M, Balestreri D, Dürig P, Schneider H. In-utero characterization of the blood flow in the Hyrtl anastomosis. PLACENTA. 2001;22:597-601. http://doi.org/10.1053/plac.2001.0685. Ullberg U, Sandstedt B, Lingman G. Hyrtl's anastomosis, the only connection between the two umbilical arteries. A study in full term placentas from AGA infants with normal umbilical artery blood flow. ACTA OBSTET GYN SCAN. 2001;80:1-6. http://doi.org/10.1034/j.1600-0412.2001.800101.x. Byrne M, Aughwane R, James JL, Hutchinson JC, Arthurs OJ, Sebire NJ, Ourselin S, David AL, Melbourne A, Clark AR. Structure-function relationships in the feto-placental circulation from in silico interpretation of micro-CT vascular structures. J THEOR BIOL. 2021;517:110630. http://doi.org/10.1016/j.jtbi.2021.110630. Walker M, Pruzinsky K, Benirschke K. Prolonged intermittent reversed end-diastolic flow in a monochorionic twin pregnancy associated with twin-to-twin transfusion syndrome and absence of Hyrtl's anastomosis. J PERINATOL. 1999;19(2):147-9. http://doi.org/10.1038/sj.jp.7200104. Tables Table 1 Fetal growth velocity in 2 fetuses GA/weeks 24 + 5 26 + 4 28 + 3 30 + 4 31 + 5 33 + 4 34 + 5 EFW of the larger fetus/g 646 813 1075 1366 1579 1842 1937 EFW of the smaller fetus/g 585 725 1005 1171 1439 1567 1755 EFW discordance ratio 9.4% 10.8% 6.5% 14.3% 11.8% 14.9% 9.4% * GA: gestational age; EFW: estimated fetal weight. Additional Declarations No competing interests reported. Supplementary Files supfiles.doc Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-2366222","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Case Report","associatedPublications":[],"authors":[{"id":162517429,"identity":"baf5a3b0-9c60-4964-99a1-3af3e1d16487","order_by":0,"name":"Liu Ziling","email":"","orcid":"","institution":"Sichuan University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Liu","middleName":"","lastName":"Ziling","suffix":""},{"id":162517430,"identity":"154f133a-1e37-4649-bfe0-ab3d9f56549b","order_by":1,"name":"Ruan Jie","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1klEQVRIiWNgGAWjYBAC+QYGNgaGAgk7fvbmAwc+/CBCCxsYGdgkS/YcSzw4s4d4LWmMG274GB/mYCNGC//hZw8+GBxmZrjB8+EwAw+DPL/YAQJaJNLMDWcYHOZjnN274XCBBYPhzNkJhLQwmEnzAG1hljm74fAMHoYEg9uEtPAf/yb9x+AwY5tEzoPDPGzEaGHIMZMGeb9HIoeBSC0SOeWGPcBAluA5ZgAMZAnCfpHvP77twY8KCTv7482PP3z4YSPPL01ACzqQIE35KBgFo2AUjALsAAAaJUNatU8XFQAAAABJRU5ErkJggg==","orcid":"","institution":"Sichuan University","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Ruan","middleName":"","lastName":"Jie","suffix":""}],"badges":[],"createdAt":"2022-12-11 08:44:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2366222/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2366222/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":31045711,"identity":"20caea50-a243-4c4e-bdbd-c31553f4dbcc","added_by":"auto","created_at":"2023-01-03 17:56:15","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":305555,"visible":true,"origin":"","legend":"\u003cp\u003eFetal growth velocity in 2 fetuses.\u003c/p\u003e\n\u003cp\u003e(The blue dots represent EFW of the larger fetus at different weeks of gestation. The green dots represent EFW of the smaller/CHD fetus at different weeks of gestation.)\u003c/p\u003e\n\u003cp\u003e* GA: gestational age; EFW: estimated fetal weight; CHD: congenital heart disease.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-2366222/v1/7b3926a49379dab61555b0b8.png"},{"id":31047399,"identity":"6b4bd358-19f1-4f1e-9f9a-e1e849db3069","added_by":"auto","created_at":"2023-01-03 18:04:16","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1537504,"visible":true,"origin":"","legend":"\u003cp\u003ePlacental perfusion staining.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;(\u003cstrong\u003eA\u003c/strong\u003e: In the 1\u003csup\u003est\u003c/sup\u003e step, the umbilical veins of both fetuses were perfused with yellow dye and pink dye, respectively. \u003cstrong\u003eB\u003c/strong\u003e: In the 2\u003csup\u003end\u003c/sup\u003e step, one umbilical artery of the smaller fetus was perfused with blue dye, and blue staining of the branch vessels of the 2 umbilical arteries of the smaller fetus and one umbilical artery of the larger fetus through the arterial-arterial anastomosis(white arrow) was observed. \u003cstrong\u003eC\u003c/strong\u003e: In the 3\u003csup\u003erd\u003c/sup\u003e step, the other umbilical artery of the larger fetus was perfused with green dye. \u003cstrong\u003eD\u003c/strong\u003e: No color mixing was observed between the 2 umbilical arteries of the larger fetus and their branch vessels. )\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-2366222/v1/89c25cd23dc8e6052bd0ce8e.png"},{"id":33269378,"identity":"a1b7ebd9-62b3-4ed5-8818-e80e8347d694","added_by":"auto","created_at":"2023-02-22 06:44:55","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2255411,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2366222/v1/2cde6844-5357-4421-8d58-11d399ab568b.pdf"},{"id":31045736,"identity":"d153ae25-aae4-4561-b79b-749ab88b8081","added_by":"auto","created_at":"2023-01-03 17:56:18","extension":"doc","order_by":16,"title":"","display":"","copyAsset":false,"role":"supplement","size":56531658,"visible":true,"origin":"","legend":"","description":"","filename":"supfiles.doc","url":"https://assets-eu.researchsquare.com/files/rs-2366222/v1/c9f8ad19f3fc74e9cab6cf79.doc"}],"financialInterests":"No competing interests reported.","formattedTitle":"The role of the absence of Hyrtl’s anastomosis in monochorionic pregnancy: friend or foe?","fulltext":[{"header":"Background","content":"\u003cp\u003eHyrtl\u0026rsquo;s anastomosis, an intra-arterial shunt, is present in approximately 96% of umbilical cords between the umbilical arteries, is usually 1.5-2cm long and positioned within 3 cm of the placental cord insertion [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. From the limited studies of singleton placentas, the presence of Hyrtl\u0026rsquo;s anastomosis plays a protective role when the placental territories supplied by the umbilical arteries are different in size[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. It equalizes pressures between the two umbilical arteries before entering the placenta and functions as a safety valve in the event of placental compression or umbilical artery blockage[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e].In placentas lacking a Hyrtl\u0026rsquo;s anastomosis, the two umbilical arteries supplied a similar area, indicating a relatively high degree of symmetry[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. However, the literature and studies on Hyrtl\u0026rsquo;s anastomosis in twin placentas are scarce.\u003c/p\u003e \u003cp\u003eHere, we reported a monochorionic diamniotic twin pregnancy complicated with type I selective fetal growth restriction. Despite discordance in placental territory and cord insertion sites, the patient had an overall good pregnancy process, suggesting that the absence of Hyrtl\u0026rsquo;s anastomosis may have played a benign role.\u003c/p\u003e"},{"header":"Case Presentation","content":"\u003cp\u003eA 29-year-old woman, gravida 4 para 0, spontaneously conceived. Ultrasound examination at 12 weeks gestation confirmed MCDA twin pregnancy. The patient was referred to our obstetrics unit at 24\u0026thinsp;+\u0026thinsp;5 weeks of gestation because of suspected fetal complex congenital heart disease(CHD). Ultrasound in our hospital suggests aortic coarctation associated with ventricular septal defect in one of the twins. At the first visit, the estimated fetal weight (EFW) of the CHD fetus fell below the 3rd percentile, and discordance between the EFW of the two fetuses was 9.4%. Therefore, type I SFGR was also diagnosed. Doppler studies of both twins as well as fetal viability were routinely performed at roughly two-weeks interval. Serial ultrasound monitoring showed normal fetal growth velocity(see in Table.1 and Figure.1), amniotic volume, umbilical artery (UA) Doppler, ductus venosus (DV) Doppler, and middle cerebral artery (MCA) Doppler in both fetuses. No significant chromosomal abnormalities in either fetus were detected by chromosome microarray analysis. The patient chose to continue the pregnancy and refused to undergo elective feticide after multidisciplinary consultation with the pediatric cardiovascular physician, neonatologist, and medical geneticist.\u003c/p\u003e \u003cp\u003eThe patient was admitted at 30 weeks of gestation for threatened preterm labor and treated with dexamethasone and magnesium sulfate, and discharged at 30\u0026thinsp;+\u0026thinsp;4 weeks after inhibition of uterine contractions. At 35\u0026thinsp;+\u0026thinsp;3 weeks` gestation, she was readmitted for cervical dilation and underwent an emergency cesarean section. The birth weight of twin female neonates was 2110/2000g (birthweight discordance ratio was 5.2%), and the 1-minute Apgar score was 10. The smaller fetus was immediately transferred to the neonatal intensive care unit and underwent single-stage surgical repair 14 days after birth.\u003c/p\u003e \u003cp\u003ePlacental perfusion staining suggests the placental territory discordance ratio was 64.2% (calculated by Image J software processing) with velamentous cord insertion of the smaller/CHD fetus. The smaller fetus had a placental area of only 13\u0026times;9 cm with an islet-like succenturiate placenta of 3\u0026times;2cm. Rarely, we found a lack of Hyrtl's anastomosis between 2 umbilical arteries in the larger fetus (see in Figure.2).\u003c/p\u003e \u003cp\u003eTo make comparisons, we also reviewed more than 50 cases of monochorionic placenta stained by perfusion from Dec.2021 to Aug. 2022 in our hospital and found that a total of 9 cases had placental territory discordance ratio greater than 50% (for more information on the images see Supplementary Files). The remaining 8 patients, except the present case, all presented with type Ⅱ-Ⅲ SFGR. Placental abruption and the smaller fetal demise occurred in one case. Considering the poor prognosis of the larger surviving fetus, the patients demand lethal induction of labor. The average gestational age at delivery for the other 7 cases was 31\u0026thinsp;+\u0026thinsp;6 weeks, and the average birthweight discordance ratio was 36.2%.\u003c/p\u003e"},{"header":"Discussion And Conclusions","content":"\u003cp\u003eIn early gestation, multiple anastomoses occur between the umbilical arteries but are subsequently reduced to one connection within the first 3 cm of cord proximal to the chorionic plate, that is, Hyrtl\u0026rsquo;s anastomosis. It was first noted by the descriptive anatomist Joseph Hyrtl, in 1870. The positive effect of this anastomosis in the singleton placentas has been reported in previous researches. The main function is to balance the pressure and flow in the two umbilical arteries helping to equalize the area of placental vascular territories. Raio[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e] reported a series of antenatal functional evaluations of this anastomosis in 41 women. The difference between the resistance indices of the two umbilical arteries was higher after than before the anastomosis. In Byrne\u0026rsquo;s models[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], placentas with an anastomosis present showed relatively small discordance between blood pressures feeding each lobe compared with larger differences predicted when an anastomosis was not included. Therefore, Hyrtl's anastomosis plays a favorable role in equalizing blood pressures between the placental lobes fed by each UA in singleton placentas, especially in the context of compensatory prevention of potential fetal compromise due to placental insufficiency and its absence is associated with an increased risk of poor outcomes.\u003c/p\u003e \u003cp\u003eStudies on Hyrtl\u0026rsquo;s anastomosis of twin placentas, especially monochorionic placentas, are rare. We finally found only one paper on this anastomosis. However, the opposite result compared to the singleton placenta was obtained. Walker]5] reported a case of monochorionic twin pregnancy associated with SFGR and suspected twin-twin transfusion syndrome(TTTS). Reversed end-diastolic flow(REDF), which is an immediate precursor of fetal demise, was noted at multiple sites in the umbilical cord of the smaller/donor twin on the day of hospital admission. Fortunately, the case had a prolonged fetal survival period of 2 weeks before delivery. Pathologic examination of the placenta after delivery disclosed an unbalanced vascular communication between the twins and the absence of Hyrtl\u0026rsquo;s anastomosis in the smaller/donor twin. The authors believe the absent Hyrtl\u0026rsquo;s anastomosis can allow adequate fetal oxygenation via the flow through one umbilical artery despite persistent REDF in the other, and allow for the relative independence of interfetal vascular anastomoses to better offset adverse effects of the twin-to-twin transfusion syndrome.\u003c/p\u003e \u003cp\u003eThe absence of Hyrtl\u0026rsquo;s anastomosis in our case also seemed to show a favorable effect similar to this literature above. However, the difference is that the absent Hyrtl\u0026rsquo;s anastomosis appears in the larger twin, not the smaller twin. In comparison to the other monochorionic placentas with large placental territory discordance, the growth difference between the twins in this case gradually decreased with increasing gestational weeks and consistently maintained good umbilical blood perfusion. The possible reason is that the two umbilical arteries of the larger fetus do not interfere with each other. Branches of one umbilical artery coincide with the smaller fetus to compensate for the relatively small placental volume, and the other umbilical artery is independent to ensure adequate cotyledonary perfusion and adequate fetal oxygenation of the larger fetus. The absence of an equalizing anastomosis allows two relatively separate and independent placental circulations. Thus, it is like transforming the placenta into an intermediate state between dichorionic and monochorionic.\u003c/p\u003e \u003cp\u003eIn conclusion, this case represents a finding of opposite effects of Hyrtl\u0026rsquo;s anastomosis in monochorionic placentas compared with singleton placentas. More cases of placental perfusion staining are needed to support our view.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eMCDA: monochorionic diamniotic\u003c/p\u003e\n\u003cp\u003eSFGR: selective fetal growth restriction\u003c/p\u003e\n\u003cp\u003eCHD:\u0026nbsp;congenital heart disease\u003c/p\u003e\n\u003cp\u003eEFW: estimated fetal weight\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eUA: umbilical artery\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDV: ductus venosus\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMCA: middle cerebral artery\u003c/p\u003e\n\u003cp\u003eTTTS: twin-twin transfusion syndrome\u003c/p\u003e\n\u003cp\u003eREDF: Reversed end-diastolic flow\u003c/p\u003e\n\u003cp\u003eGA: gestational age\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate:\u003c/strong\u003e Published case report comply with the guidelines for human studies and was conducted ethically in accordance with the World Medical Association Declaration of Helsinki. Written informed consent was obtained from the patient for publication of this case report and any accompanying images.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication:\u003c/strong\u003e Written informed consent was obtained from the patient for publication of this case report and any accompanying images.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials:\u003c/strong\u003e The datasets used and/or analyzed during the current study are available\u003c/p\u003e\n\u003cp\u003efrom the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests:\u003c/strong\u003e None declared.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions:\u003c/strong\u003e LZ participated in the writing, and organization of the manuscript. RJ took charge in patient consultation and placental perfusion, and coordinated revising of the manuscript. All authors listed have read and approved the fnal version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements:\u003c/strong\u003e Not applicable.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eSherer DM, Al-Haddad S, Cheng R, Dalloul M. Current Perspectives of Prenatal Sonography of Umbilical Cord Morphology. Int J Womens Health. 2021;13:939-71. http://doi.org/10.2147/IJWH.S278747.\u003c/li\u003e\n\u003cli\u003eRaio L, Ghezzi F, di Naro E, Franchi M, Balestreri D, D\u0026uuml;rig P, Schneider H. In-utero characterization of the blood flow in the Hyrtl anastomosis. PLACENTA. 2001;22:597-601. http://doi.org/10.1053/plac.2001.0685.\u003c/li\u003e\n\u003cli\u003eUllberg U, Sandstedt B, Lingman G. Hyrtl\u0026apos;s anastomosis, the only connection between the two umbilical arteries. A study in full term placentas from AGA infants with normal umbilical artery blood flow. ACTA OBSTET GYN SCAN. 2001;80:1-6. http://doi.org/10.1034/j.1600-0412.2001.800101.x.\u003c/li\u003e\n\u003cli\u003eByrne M, Aughwane R, James JL, Hutchinson JC, Arthurs OJ, Sebire NJ, Ourselin S, David AL, Melbourne A, Clark AR. Structure-function relationships in the feto-placental circulation from in silico interpretation of micro-CT vascular structures. J THEOR BIOL. 2021;517:110630. http://doi.org/10.1016/j.jtbi.2021.110630.\u003c/li\u003e\n\u003cli\u003eWalker M, Pruzinsky K, Benirschke K. Prolonged intermittent reversed end-diastolic flow in a monochorionic twin pregnancy associated with twin-to-twin transfusion syndrome and absence of Hyrtl\u0026apos;s anastomosis. J PERINATOL. 1999;19(2):147-9. http://doi.org/10.1038/sj.jp.7200104.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":" \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cdiv class=\"SimplePara\"\u003eFetal growth velocity in 2 fetuses\u003c/div\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cdiv class=\"SimplePara\"\u003eGA/weeks\u003c/div\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cdiv class=\"SimplePara\"\u003e24\u0026thinsp;\u003csup\u003e+\u0026thinsp;5\u003c/sup\u003e\u003c/div\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cdiv class=\"SimplePara\"\u003e26\u0026thinsp;\u003csup\u003e+\u0026thinsp;4\u003c/sup\u003e\u003c/div\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cdiv class=\"SimplePara\"\u003e28\u0026thinsp;\u003csup\u003e+\u0026thinsp;3\u003c/sup\u003e\u003c/div\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cdiv class=\"SimplePara\"\u003e30\u0026thinsp;\u003csup\u003e+\u0026thinsp;4\u003c/sup\u003e\u003c/div\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cdiv class=\"SimplePara\"\u003e31\u0026thinsp;\u003csup\u003e+\u0026thinsp;5\u003c/sup\u003e\u003c/div\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cdiv class=\"SimplePara\"\u003e33\u0026thinsp;\u003csup\u003e+\u0026thinsp;4\u003c/sup\u003e\u003c/div\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cdiv class=\"SimplePara\"\u003e34\u0026thinsp;\u003csup\u003e+\u0026thinsp;5\u003c/sup\u003e\u003c/div\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cdiv class=\"SimplePara\"\u003eEFW of the larger fetus/g\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cdiv class=\"SimplePara\"\u003e646\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cdiv class=\"SimplePara\"\u003e813\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cdiv class=\"SimplePara\"\u003e1075\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cdiv class=\"SimplePara\"\u003e1366\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cdiv class=\"SimplePara\"\u003e1579\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cdiv class=\"SimplePara\"\u003e1842\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cdiv class=\"SimplePara\"\u003e1937\u003c/div\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cdiv class=\"SimplePara\"\u003eEFW of the smaller fetus/g\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cdiv class=\"SimplePara\"\u003e585\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cdiv class=\"SimplePara\"\u003e725\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cdiv class=\"SimplePara\"\u003e1005\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cdiv class=\"SimplePara\"\u003e1171\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cdiv class=\"SimplePara\"\u003e1439\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cdiv class=\"SimplePara\"\u003e1567\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cdiv class=\"SimplePara\"\u003e1755\u003c/div\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cdiv class=\"SimplePara\"\u003eEFW discordance ratio\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cdiv class=\"SimplePara\"\u003e9.4%\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cdiv class=\"SimplePara\"\u003e10.8%\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cdiv class=\"SimplePara\"\u003e6.5%\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cdiv class=\"SimplePara\"\u003e14.3%\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cdiv class=\"SimplePara\"\u003e11.8%\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cdiv class=\"SimplePara\"\u003e14.9%\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cdiv class=\"SimplePara\"\u003e9.4%\u003c/div\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"8\"\u003e* GA: gestational age; EFW: estimated fetal weight.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003cbr/\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Hyrtl’s anastomosis, monochorionic diamniotic twin pregnancy, selective fetal growth restriction, placental territory discordance","lastPublishedDoi":"10.21203/rs.3.rs-2366222/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2366222/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground: \u003c/strong\u003eHyrtl’s anastomosis, an intra-arterial shunt, plays a protective role when the placental territories supplied by the umbilical arteries are different in size. Its absence is associated with an increased risk of poor outcomes in singleton pregnancy. However, the literature and studies on the effect of absent Hyrtl’s anastomosis in twin placentas are rare.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCase Presentation: \u003c/strong\u003eWe present a case of a monochorionic diamniotic(MCDA) twin pregnancy complicated with type I selective fetal growth restriction(SFGR). Despite discordance in placental territory and cord insertion sites, the patient had an overall good pregnancy process, suggesting that the absence of Hyrtl’s anastomosis may have played a benign role.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions: \u003c/strong\u003eThe absence of Hyrtl’s anastomosis in our case seemed to show a favorable effect, representing a finding of opposite effects in monochorionic placentas compared with singleton placentas.\u003c/p\u003e","manuscriptTitle":"The role of the absence of Hyrtl’s anastomosis in monochorionic pregnancy: friend or foe?","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-01-03 17:56:10","doi":"10.21203/rs.3.rs-2366222/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"b28c07e9-638e-49ef-8a25-a7125ae9c347","owner":[],"postedDate":"January 3rd, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2023-02-22T06:44:42+00:00","versionOfRecord":[],"versionCreatedAt":"2023-01-03 17:56:10","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-2366222","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2366222","identity":"rs-2366222","version":["v1"]},"buildId":"cBFmMYwuxLRRLfASyISRj","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}