jabbrv-ltwa-all.ldf jabbrv-ltwa-en.ldf Birth outcomes associated with assisted vaginal birth in an occipito-posterior position: secondary analyses of the Instrumental Delivery & UltraSound randomised controlled trial and cohort study.

jabbrv-ltwa-all.ldf jabbrv-ltwa-en.ldf Birth outcomes associated with assisted vaginal birth in an occipito-posterior position: secondary analyses of the Instrumental Delivery & UltraSound randomised controlled trial and cohort study. | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL BJOG: An International Journal of Obstetrics and Gynaecology This is a preprint and has not been peer reviewed. Data may be preliminary. 29 May 2025 V1 Latest version Share on jabbrv-ltwa-all.ldf jabbrv-ltwa-en.ldf Birth outcomes associated with assisted vaginal birth in an occipito-posterior position: secondary analyses of the Instrumental Delivery & UltraSound randomised controlled trial and cohort study. Authors : Hayes L 0000-0003-1760-1008 , Ramphul M , and Deirdre Murphy J 0000-0001-6074-6718 [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.174854170.00654186/v1 279 views 141 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Objective: To investigate the morbidity associated with assisted vaginal birth (AVB) and an occipito-posterior (OP) fetal head position. Design: Observational study based on secondary analyses of a randomised controlled trial and cohort study. Setting: Two university affiliated maternity hospitals in Ireland. Population: A cohort of 1081 nulliparous women at term who experienced AVB. Methods: Univariable and multivariable logistic regression analyses were performed. Main Outcome Measures: Postpartum haemorrhage (PPH), obstetric anal sphincter injury (OASI), fetal acidosis, neonatal trauma, failed AVB leading to caesarean section (CS). Results: Of the 1081 AVBs, a total of 192 (17.8%) had an OP position with 103 of these (53.6%) rotated to occiptio-anterior (OA) prior to AVB and 89 (46.4%) delivered direct OP. AVB completed in a direct OP position compared with OP rotated to OA was associated with an increased risk of PPH (34% vs 15%, adjusted Odds Ratio 2.98; 95% Confidence Interval 1.48 to 6.02), OASI (16% vs 2%, adj OR 19.56;95% CI 4.09 to 93.62) and CS (27% versus 5%, adj OR 7.24; 95% CI 2.63 to 19.93). There were no significant differences in neonatal outcomes. The diagnosis of OP was incorrectly assigned in 35 of the 192 cases (18.2%) but did not impact on morbidity outcomes compared to known OP. Conclusions: This study highlights the increased risk of PPH, OASI, and failed AVB when attempting to deliver the baby in a direct OP position rather than rotating to OA. This has important implications for training and guidelines. Introduction Fetal malposition refers to orientation of the fetal head in an occipito-posterior (OP) or occipito-transverse (OT) position. 1 It is a common problem, with a prevalence of 33-58% in the first stage of labour and 12-22% in the second stage of labour. 2-3 There are many factors associated with fetal malposition that include nulliparity, increased maternal body mass index (BMI), advanced maternal age, pelvic shape, fetal macrosomia, and use of epidural analgesia. 4-5 Fetal malposition is associated with assisted vaginal birth (AVB) and caesarean section (CS), and has been shown to impact negatively on maternal, neonatal and procedural outcomes when compared to occipito-anterior (OA) position. 4-6 Persistent OP has increased risks in labour including a twofold increase in rates of AVB, and threefold increase in rates of CS. 5. 7-9 Specific risks associated with vaginal birth in an OP position include obstetric anal sphincter injury (OASI), postpartum haemorrhage (PPH) and neonatal trauma. 10-14 The optimal approach to expediting vaginal birth in the second stage of labour with an OP position is unclear. The Assisted Vaginal Birth guideline of the Royal College of Obstetricians and Gynaecologists (RCOG) supports use of rotational vacuum, rotational forceps and manual rotation followed by vacuum or direct traction forceps. 15 The aim with each approach is to achieve rotation of the fetal head to an OA position with a higher chance of successful vaginal birth. What is less clear is whether it is acceptable to deliver the baby in a direct OP position, often by forceps, where the presenting diameters are wider which may lead to neonatal and maternal pelvic floor trauma. The alternative is to deliver by second stage caesarean section which can be complicated by fetal head impaction and extension of the uterine incision. 6, 16 There are no randomised controlled trials addressing this question and observational studies based on routinely collected data rely on recording of the procedure after the birth which may not capture attempts at rotation and diagnostic errors. In the Instrumental Delivery & UltraSound (IDUS) randomised controlled trial (RCT) we evaluated whether ultrasound assessment prior to AVB improved the accuracy of diagnosis of the fetal head position and reduced morbidity. 17 We conducted a contemporaneous cohort study that evaluated a total population of AVBs to enhance our understanding of the trial findings and the implications for routine care. 18 In each case, the position of the fetal head was documented prior to attempted AVB and verified by the position and fetal head markings at birth. This combined cohort presents a unique opportunity to evaluate the maternal and neonatal risks associated with AVB and an OP position. Our aims were threefold. First, we compared outcomes for attempted AVB with an OP position compared to an OA position. Second, we compared AVB outcomes with an OP position where the fetal head was rotated to OA compared to attempted AVB in a direct OP position. Third, we compared outcomes where there was an error in diagnosing OP position compared to AVB where the OP position was correctly identified. This approach addresses important clinical questions relevant to obstetric practice. Study Participants The background and methods of the IDUS randomised trial have been reported previously. 17, 19 To summarise, between June 2011 and December 2012, we recruited women aiming to deliver vaginally from two teaching hospitals in Ireland with a combined annual birth rate of 13,500. In these units, AVBs are carried out by obstetricians of varying experience with a consultant supervising the labour ward onsite during the day and offsite at night. We included nulliparous women at term (at least 37 completed weeks’ gestation) with singleton cephalic pregnancies, and excluded women under 18 years of age, with limited understanding of English, or with a contraindication to AVB. Eligible women provided written consent. We randomised 514 women who required an AVB to either usual care (clinical assessment of the fetal head position alone) or ultrasound (clinical assessment and ultrasound assessment of the fetal head position). Patient demographics, detailed procedural information, and documentation of the fetal head position prior to instrument application and at birth were recorded. In addition, the midwife or neonatologist who attended the birth examined the baby and recorded the markings of the instrument on a drawing of the head and face which validated the fetal head position at the time of instrument application. The cohort study commenced in the larger maternity hospital in February 2013, two months after the randomised trial was completed in that institution and ended in November 2013. 18 Every nulliparous woman with a singleton cephalic pregnancy who had an AVB at term during that period was included in the study. A research team consisting of midwives and obstetricians identified cases daily from labour ward records and the electronic maternity database. Similar data to the RCT were recorded in terms of patient demographics and detailed labour and procedural information. Obstetricians, midwives and neonatologists were asked to complete the same documentation and drawings as used in the trial to indicate the fetal head position at the outset and as verified at the time of birth. Outcome measures The outcome measures for the mother included postpartum haemorrhage (PPH; estimated blood loss more than 500mls), obstetric anal sphincter tears (OASI; third or fourth degree tear), shoulder dystocia, prolonged hospital stay (more than three days) and postnatal readmission (all causes). The outcome measures for the neonate included neonatal trauma (excluding minor bruising and skin abrasions, including facial nerve palsy, Erb’s palsy, any fracture, retinal haemorrhage, cephalhaematoma and any cerebral haemorrhage), low Apgar score (less than seven at five minutes), fetal acidosis (arterial pH less than 7.10) and admission to the neonatal intensive care unit (NICU). The procedural outcomes included sequential use of instruments (usually vacuum followed by forceps), more than three pulls with an instrument(s), a second operator involved in the birth, transfer to an operating theatre, caesarean section following a failed attempt at AVB, and decision to delivery interval (DDI), Statistical analysis Data collected for the trial and cohort study had been merged in a single database and were fully anonymised. The database was subdivided to allow subgroup analysis according to fetal head position (OA, OT, OP) prior to attempting AVB. We used descriptive statistics for the maternal, neonatal, labour and procedural factors to characterise the study population in relation to the fetal head position. Results are reported as Odds Ratios (OR) and 95% Confidence Intervals (CI). The morbidity outcome analyses were completed in three stages; i) OP compared to OA, ii) Direct OP compared to OP rotated and iii) Error in OP diagnosis compared to OP correctly diagnosed. Multivariable logistic regression analyses were performed to address potential confounding factors. Factors were chosen for the regression analyses primarily based on statistically significant differences between the two groups for baseline clinical variables. We also included birth weight as it is likely to have an important bearing on AVB outcomes. Results are reported as proportions, crude odds ratios (OR) and adjusted odds ratios (adj OR) with 95% confidence intervals (CI). SPSS version 25 was used for all analyses. Results Of the 1081 AVBs, a total of 192 (17.8%) had an OP position with 103 of these (53.6%) rotated to OA prior to AVB and 89 (46.4%) delivered direct OP. After the birth, it was apparent that 35 cases (18.2%) had been OP at the outset and were incorrectly diagnosed as OA or OT. Factors associated with an OP position included maternal obesity (BMI ≥30kg/m 2 ) (Odds Ratio 1.83; 95% Confidence Interval 1.09 to 3.05) and male infant (OR 1.51; 1.09 to 2.10) (Table 1). There were more high birth weight babies (≥ 4.0kg) in the OP group but the difference was not statistically significant (18% versus 13%, OR 1.46; 95% CI 0.95 to 2.25). Labour characteristics associated with OP position included prolonged first and second stage of labour, pathological CTG, fetal blood sampling, mid-cavity station and marked caput succedaneum (Table 2). OP position compared with OA was associated with an increased risk of sequential use of instruments (16% versus 7%, adjusted OR 2.36; 95% CI 1.42 to 3.92), transfer to theatre (23% versus 4%, adj OR 5.88; 3.42 to 10.09) and CS after a failed attempt at AVB (7% versus 0.3%, adj OR 19.20; 4.19 to 88.08) (Table 3). The associations were slightly attenuated after controlling for potential confounding factors including birth weight. Trainee obstetricians performed the majority of AVBs irrespective of the fetal head position (77-80%) but OP position was associated with an increased risk of the birth being completed by more than one operator (25% versus 6%, adj OR 4.13; 2.56 to 6.65). Mean decision to delivery interval was almost 7 minutes longer with an OP position (difference between means 6.9 mins; 95% CI 3.0 to 12.4). Women who had an AVB with an OP position were more likely to experience an OASI (10% versus 5%, adj OR 1.92; 95% CI 1.02 to 3.62) and postnatal readmission (3% versus 1%, adj OR 3.20; 95% CI 1.02 to 10.02) (Table 4). Neonatal trauma occurred more often with OP position but did not reach statistical significance (8% versus 5%, adj OR 1.81; 95% CI 0.95 to 3.46) and rates of low Apgar score, fetal acidosis and NICU admission were similar between the groups. There was increased maternal morbidity when the baby was delivered in a direct OP position compared with rotation to OA (Table 5). There was a higher rate of PPH (34% versus 15%, adj OR 3.02 (95% CI 1.43 to 6.38), OASI (22% versus 2%, adj OR 14.75; 95% CI 3.10 to 70.10) and caesarean section (27% versus 5%, adj OR 7.29; 95% CI 2.56 to 20.77). Neonatal outcomes were similar in both groups. The diagnosis of OP was incorrectly assigned as OA or OT in 35 of the 192 cases (18.2%) but this did not impact significantly on morbidity outcomes compared to known OP. Discussion Main findings In this cohort study of women who required an assisted vaginal birth, OP position was associated with an increased risk of OASI, sequential instrument use, and CS after a failed attempt at AVB. When performed in a direct OP position rather than rotated to OA, AVB was associated with a marked increase in the risk of PPH, OASI and CS. Incorrect diagnosis of the fetal head position did not appear to augment these risks. Adverse neonatal outcomes were not significantly increased. Strengths and limitations The study population was recruited from two high-volume maternity hospitals and included a broad spectrum of women with a range of indications for AVB. Operators at all levels of experience were included. The results are generalisable to other centres where vacuum and forceps are commonly performed for fetal malposition. Medical records and case report forms were cross-checked with computerised records which facilitated checks for accuracy and minimised missing data. The reported findings prior to AVB, procedural details and instrument application were validated by an obstetrician, midwife and neonatologist which improved data reliability. It was challenging in some cases to differentiate between incorrect diagnosis of the fetal head position and suboptimal instrument placement, particularly in cases of vacuum assisted birth. Where there was doubt, the assigned position was assumed to be correct, and it is possible that the rate of incorrect diagnosis was higher than reported. The study sample was sufficient to evaluate important maternal complications including OASI, PPH, failed AVB and postnatal readmission. It was insufficient to address less common adverse neonatal outcomes such as encephalopathy and may have been underpowered to evaluate neonatal trauma. Comparison with other studies We confirmed the known associations between OP and complex operative birth, as well as the increased risks of adverse maternal and neonatal outcomes. 5-12 A large retrospective population-based study in Canada highlighted the association between OP, assisted vaginal birth and OASI but unlike our study their database was unable to identify cases where rotation had been completed before traction. 9 A study from the US compared the effect of non-rotated OP forceps and rotated forceps on perineal tears, and as with our study, reported an increased risk of OASI with non-rotation (43% versus 24%). 13 The very high rates of OASI in the US study probably reflect midline episiotomy. By contrast, our study included direct OP vacuum and forceps births, use of medio-lateral episiotomy, and highlighted the additional increased risks of PPH, emergency CS and hospital readmission. There is a recognised risk of neonatal trauma with AVB and OP position, but we did not find any further exacerbation in the risk with AVB in a direct OP position, or where there was an error in the diagnosis of the position prior to instrument application. 6, 8, 14 Implications The AVB guidelines from the United Kingdom, Canada, Australia and New Zealand support the use of rotational vacuum, rotational forceps and manual rotation followed by direct traction forceps/vacuum for the management of OP position. 15, 20-21 The Canadian guidelines recommend manual rotation as a prophylactic measure although a systematic review suggests that while this may shorten the duration of the second stage of labour there is no difference in maternal and fetal outcomes. 20, 22 The challenge for the clinician is what approach to take when attempts at rotation have been unsuccessful and the fetal head position remains OP. Our data suggest that there is significant maternal morbidity with AVB completed in a direct OP position and that this should be balanced with the risks of CS in the second stage of labour. 6, 23 Conclusion This study confirms the known complexity associated with expediting birth in the second stage of labour with an OP position. It highlights the significant risks of maternal morbidity when attempting to complete an AVB with the fetal head in a direct OP position rather than prior rotation to OA. This has important implications for obstetric training and practice guidelines. Disclosure Deirdre J Murphy provides medico-legal expert opinions including aspects of Assisted Vaginal Birth. There are no other conflicts of interest to declare. Contribution to authorship DJM had the original idea for the study. DJM and MR designed the trial and cohort study. DJM and LH performed the analyses and drafted the article, which was revised by all authors. DJM is the guarantor. Details of ethics approval We received ethical approval for the IDUS trial from the Research Ethics Committee (REC) in the Coombe Women & Infants University Hospital on 5 October 2010, and from the REC in the Mid-Western Regional Maternity Hospital, Limerick, on 9 August 2011. We received ethical approval for the cohort study from the REC in the Coombe Women & Infants University Hospital on 12 December 2012. The chairman of the Coombe Hospital REC confirmed that ethical approval was not required for the secondary analyses of the anonymised dataset (Study No. 09 – 2023). The IDUS trial was prospectively registered with International Standard Randomised Controlled Trial Number (ISRCTN): 72230496. Data sharing The data included in this study are available on reasonable request from the corresponding author. Acknowledgements: We would like to acknowledge the patients and staff in the involved hospitals for supporting the IDUS trial and cohort study and the original IDUS trial team. References 1. Murphy DJ. Malposition, Malpresentation and Cephalopelvic Disproportion. In Arulkumaran, S., Ledger, W., Denny, L. and Doumouchtsis, S. eds., 2019. Oxford textbook of Obstetrics and Gynaecology. Oxford University Press. 2. Souka AP, Haritos T, Basayiannis K, Noikokyri N, Antsaklis A. Intrapartum ultrasound for the examination of the fetal head position in normal and obstructed labor. J Matern Fetal Neonatal Med. 2003;13(1):59–63. 3. Akmal S, Tsoi E, Howard R, Osei E, Nicolaides KH. Investigation of occiput posterior delivery by intrapartum sonography. Ultrasound Obstet Gynecol. 2004;24(4):425–8. 4. Barrowclough J, Kool B, Crowther C. Fetal malposition in labour and health outcomes for women and their newborn infants: A retrospective cohort study. PLoS One. 2022;17(10):e0276406. 5. Cheng YW, Shaffer BL, Caughey AB. Associated factors and outcomes of persistent occiput posterior position: a retrospective cohort study from 1976 to 2001. J Matern Fetal Neonatal Med. 2006;19:563–8. 6. Murphy DJ, Liebling RE, Verity L, Swingler R, Patel R. Early maternal and neonatal morbidity associated with operative delivery in second stage of labour: a cohort study. Lancet. 2001;358(9289):1203-7. 7. Fitzpatrick M, McQuillan K, O’Herlihy C. Influence of persistent occiput posterior position on delivery outcome. Obstet Gynecol. 2001;98:1027–31. 8. Cheng YW, Shaffer BL, Caughey AB. The association between persistent occiput posterior position and neonatal outcomes. Obstet Gynecol. 2006;107:837–44. 9. Foggin HH, Albert AY, Minielly NC, et al. Labor and delivery outcomes by delivery method in term deliveries in occiput posterior position: a population-based retrospective cohort study. Am J Obstet Gynecol Glob Rep. 2022;2:100080. 10. Senecal J, Xiong X, Fraser WD. Pushing Early Or Pushing Late with Epidural study group. Effect of fetal position on second-stage duration and labor outcome. Obstet Gynecol. 2005;105:763–72. 11. Benavides L, Wu JM, Hundley AF, Ivester TS, Visco AG. The impact of occiput posterior fetal head position on the risk of anal sphincter injury in forceps-assisted vaginal deliveries. Am J Obstet Gynecol. 2005;192:1702–6. 12. Wu JM, Williams KS, Hundley AF, Connolly AM, Visco AG. Occiput posterior fetal head position increases the risk of anal sphincter injury in vacuum-assisted deliveries. Am J Obstet Gynecol. 2005;193:525–8. 13. Bradley MS, Kaminski RJ, Streitman DC, Dunn SL, Krans EE. Effect of rotation on perineal lacerations in forceps-assisted vaginal deliveries. Obstet Gynecol. 2013;122:132–74. 14. Dahlqvist K, Jonsson M. Neonatal outcomes of deliveries in occiput posterior position when delayed pushing is practiced: a cohort study. BMC Pregnancy Childbirth. 2017;17:377. 15. Murphy DJ, Strachan BK, Bahl R, on behalf of the Royal College of Obstetricians Gynaecologists. Assisted Vaginal Birth. BJOG. 2020;127:e70–e112. 16. Jones NW, Mitchell EJ, Wakefield N, Knight M, Dorling J, Thornton JG, Walker KF. Impacted fetal head during second stage Caesarean birth: A prospective observational study. Eur J Obstet Gynecol Reprod Biol. 2022;272:77-81. 17. Ramphul M, Poh VO, Burke G, Kennelly M, Said A, Montgomery AA, et al. IDUS – Instrumental Delivery & UltraSound. A multi-centre randomised controlled trial of ultrasound assessment of the fetal head position versus standard care as an approach to prevent morbidity at instrumental delivery. BJOG. 2014;121(8):1029-38. 18. Butler K, Ramphul M, Dunney C, Farren M, McSweeney A, McNamara K et al. A prospective cohort study of the morbidity associated with operative vaginal deliveries performed by day and night. BMJ Open. 2014;4(10):e006291. 19. Murphy DJ, Burke G, Montgomery AA, Ramphul M. Study protocol. IDUS – Instrumental delivery & ultrasound: a multi-centre randomised controlled trial of ultrasound assessment of the fetal head position versus standard care as an approach to prevent morbidity at instrumental delivery. BMC Pregnancy Childbirth. 2012;12:95. 20. Hobson S, Cassell K, Windrim R, Cargill Y. No. 381-assisted vaginal birth. J Obstet Gynaecol Canada. 2019;41(6):870-82. 21. RANZCOG. The Women’s Health Committee. The Royal Australian and New Zealand College of Obstetricians and Gynaecologists. Instrumental vaginal birth; March 2016. 22. Bertholdt C, Morel O, Zuily S, Ambroise-Grandjean G. Manual rotation of occiput posterior or transverse positions: a systematic review and meta-analysis of randomized controlled trials. Am J Obstet Gynecol. 2022;226(6):781-793. 23. Thierens S, van Binsbergen A, Nolens B, van den Akker T, Bloemenkamp K, Rijken MJ. Vacuum extraction or caesarean section in the second stage of labour: A systematic review. BJOG. 2023;130(6):586-98. Table 1 Maternal & neonatal characteristics in relation to fetal head position at Assisted Vaginal Birth Maternal Maternal age > 35 years 15 (7.8) 24 (9.4) 64 (10.1) 0.76 (0.42 to 1.36) BMI ≥ 30.0 kg/m 2 25 (13.0) 26 (10.2) 48 (7.6) 1.83 (1.09 to 3.05) * Non-Caucasian 26 (13.5) 49 (19.2) 118 (18.6) 0.69 (0.43 to 1.08) Current smoker 17 (8.9) 15 (5.9) 46 (7.3) 1.24 (0.69 to 2.22) Alcohol in pregnancy 2 (1.0) 2 (0.8) 7 (1.1) 0.94 (0.19 to 4.58) Sub-fertility (treated) 10 (5.2) 11 (4.3) 35 (5.5) 0.94 (0.46 to 1.94) Diabetes (any) 9 (4.7) 4 (1.6) 30 (4.7) 0.99 (0.46 to 2.12) Pre-eclampsia 4 (2.1) 5 (2.0) 15 (2.4) 0.88 (0.29 to 2.68) SGA 4 (2.1) 8 (3.1) 30 (4.7) 0.43 (0.15 to 1.23) Neonatal Male infant 115 (59.9) 133 (52.2) 315 (49.7) 1.51 (1.09 to 2.10) * HC ≥ 37.0cm 21 (10.9) 36 (14.1) 62 (9.8) 1.13 (0.67 to 1.91) Birthweight ≥ 4.0kg 35 (18.2) 42 (16.5) 84 (13.2) 1.46 (0.95 to 2.25) Birthweight < 2.5kg 1 (0.5) 2 (0.8) 15 (2.4) 0.22 (0.03 to 1.65) i Odds Ratio calculated for OP compared to OA * p < 0.05 OP occipito-posterior; OT occipito-transverse; OA occipito-anterior BMI - Body Mass Index measured as booking weight divided by the square of height (kg/m 2 ) SGA – small for gestational age on ultrasound scan (abdominal circumference <10 th centile) HC - Head Circumference; large ≥ 37.0cm Table 2 Labour characteristics in relation to fetal head position at Assisted Vaginal Birth (AVB) Induction of labour 88 (45.8) 114 (55.3) 312 (49.2) 0.87 (0.63 to 1.21) 1 st stage of labour > 12 hours 20 (10.4) 27 (10.6) 38 (6.0) 1.83 (1.04 to 3.23) * 2 nd stage of labour > 2 hours 110 (57.3) 150 (58.8) 298 (47.0) 1.51 (1.09 to 2.09) * Oxytocin in 1 st stage of labour 118 (61.5) 179 (70.2) 379 (59.8) 1.06 (0.76 to 1.48) Oxytocin in 2 nd stage of labour 137 (71.4) 203 (79.6) 449 (70.8) 1.03 (0.72 to 1.47) Meconium stained liquor 42 (21.9) 56 (22.0) 154 (24.3) 0.87 (0.59 to 1.29) Pathological CTG (1 st stage) 26 (13.5) 27 (10.6) 51 (8.0) 1.79 (1.08 to 2.96) * Pathological CTG (2 nd stage) 104 (54.2) 120 (47.1) 317 (50.0) 1.18 (0.86 to 1.63) Fetal blood sample (FBS) 72 (37.5) 72 (28.2) 162 (25.6) 1.75 (1.24 to 2.46) * Low pH <7.20 on FBS 4/72 (5.6) 3/72 (4.3) 3/162 (1.9) 3.02 (0.66 to 13.86) Regional anaesthesia 173 (90.1) 242 (94.9) 550 (86.8) 1.39 (0.82 to 2.35) Local anaesthesia 19 (9.9) 13 (5.1) 84 (13.2) 0.72 (0.43 to 1.22) Mid- cavity station (0/+1 cm) 160 (83.3) 201 (78.8) 414 (65.3) 2.66 (1.76 to 4.02) * Caput succedaneum ≥ ++ 65 (33.9) 82 (32.2) 131 (20.7) 1.97 (1.38 to 2.80) * Moulding ≥ ++ 8 (4.2) 13 (5.1) 14 (2.2) 1.93 (0.80 to 4.66) i Odds Ratio calculated for OP compared to OA * p < 0.05 jabbrv-ltwa-all.ldf jabbrv-ltwa-en.ldf OP occipito-posterior; OT occipito-transverse; OA occipito-anterior Caput succedaneum refers to the oedematous scalp swelling; + minimal; ++ moderate; +++ severe Moulding refers to remodelling of the skull bones; + bones touch, ++ bones overlap but separate easily with digital pressure and +++ bones overlap but are not separable with digital pressure Table 3 Procedural outcomes in relation to fetal head position at Assisted Vaginal Birth (AVB) Completed AVB 163 (84.9) 236 (92.5) 622 (98.1) 0.11 (0.05 to 0.22) * 0.14 (0.07 to 0.28) * Vacuum - primary instrument 115 (59.9) 193 (75.7) 423 (66.7) 0.75 (0.53 to 1.04) 0.83 (0.58 to 1.16) Forceps - primary instrument 61 (31.8) 57 (22.4) 209 (33.0) 0.95 (0.67 to 1.34) 0.88 (0.62 to 1.26) Sequential use of instruments 30 (15.6) 33 (12.9) 46 (7.3) 2.37 (1.45 to 3.87) * 2.36 (1.42 to 3.92) * More than 3 pulls 27 (14.1) 28 (11.0) 33 (5.2) 2.98 (1.74 to 5.10) * 3.20 (1.83 to 5.58) * Transfer to theatre 45 (23.4) 40 (15.7) 26 (4.1) 7.16 (4.28 to 12.0) * 5.88 (3.42 to 10.1) * Caesarean section (CS) 29 (15.1) 18 (7.1) 5 (0.8) 22.4 (8.53 to 58.7) * 17.5 (6.55 to 46.7) * CS after failed AVB 13 (6.8) 13 (5.1) 2 (0.3) 23.0 (5.13 to 102.6) * 19.2 (4.19 to 88.1) * CS no attempt at AVB 16 (8.3) 5 (2.0) 3 (0.5) 19.1 (5.51 to 66.4) * 13.6 (3.85 to 48.3) * Trainee operator 147 (76.6) 201 (78.8) 504 (79.5) 0.84 (0.57 to 1.24) 0.73 (0.49 to 1.10) Consultant operator 45 (23.4) 54 (21.2) 130 (20.5) 1.19 (0.81 to 1.75) 1.37 (0.91 to 2.05) More than 1 operator 47 (24.5) 31 (12.2) 39 (6.2) 4.95 (3.12 to 7.85) * 4.13 (2.56 to 6.65) * Mean DDI in minutes (SD) † 18.0 (13.9) 15.1 (10.0) 11.1 (6.3) 6.9 (3.0 to 12.4) * i Odds Ratio calculated for OP compared to OA ii Adjusted for maternal BMI, male infant, birth weight, labour duration, pathological CTG 1 st stage * p < 0.05 OP occipito-posterior; OT occipito-transverse; OA occipito-anterior † DDI – Decision to delivery interval - the time interval between the decision to intervene and birth of the baby; Difference in means (Standard Deviation) Table 4 Maternal & neonatal outcomes in relation to fetal head position at Assisted Vaginal Birth Maternal Postpartum haemorrhage 45 (23.4) 55 (21.6) 99 (15.6) 1.65 (1.11 to 2.46) * 1.39 (0.92 to Episiotomy iii 153/163 (94.4) 207/237 (87.3) 517/629 (82.2) 3.68 (1.82 to 7.44) * 3.91 (1.85 to 8.23) * OASI iii 16/163 (9.8) 11/237 (4.6) 33/629 (5.2) 1.97 (1.05 to 3.67) * 1.92 (1.02 to 3.62) * Shoulder dystocia 5 (2.6) 12 (4.7) 29 (4.6) 0.56 (0.21 to 1.46) 0.42 (0.16 to 1.14) Postpartum antibiotics 32 (16.7) 36 (14.1) 109 (17.2) 0.96 (0.63 to 1.48) 0.85 (0.54 to 1.33) Postnatal stay >3days 32 (16.7) 48 (18.8) 115 (18.1) 0.90 (0.59 to 1.39) 0.87 (0.56 to 1.36) Postnatal readmission 6 (3.1) 2 (0.8) 8 (1.3) 2.52 (0.87 to 7.37) 3.20 (1.02 to 10.0) * Neonatal Apgar score ≤ 3 at 1 min 0 (0.0) 0 (0.0) 2 (0.3) ___ Apgar score < 7 at 5 min 11 (5.7) 18 (7.1) 36 (5.7) 1.01 (0.50 to 2.02) 0.98 (0.48 to 1.99) Arterial pH <7.10 11 (5.7) 18 (7.1) 36 (5.7) 1.01 (0.50 to 2.02) 0.98 (0.48 to 1.99) Neonatal trauma† 16 (8.3) 24 (9.4) 30 (4.7) 1.83 (0.98 to 3.44) 1.81 (0.95 to 3.46) Neonatal unit admission 20 (10.4) 37 (14.5) 71 (11.2) 0.92 (0.55 to 1.56) 0.95 (0.56 to 1.63) i Odds Ratio calculated for OP compared to OA ii Adjusted for maternal BMI, male infant, birth weight, labour duration, pathological CTG in 1 st stage iii Denominator refers to vaginal births only * p < 0.05 OP occipito-posterior; OT occipito-transverse; OA occipito-anterior; CI Confidence Interval † Excluding bruising and skin abrasions, including cephalhaematoma, facial nerve palsy, Erb’s palsy, fracture, retinal haemorrhage, intracranial haemorrhage Table 5 Adverse maternal, neonatal and procedural outcomes in relation to occipito-posterior (OP) position at Assisted Vaginal Birth Maternal Postpartum haemorrhage 30 (33.7) 15 (14.6) 2.98 (1.48 to 6.02) * 3.02 (1.43 to 6.38) * 11 (31.4) 34 (21.7) 1.66 (0.74 to 3.72) 2.23 (0.91 to 5.45) Obstetric Anal Sphincter Injury iii 14/65 (21.5) 2/98 (2.0) 13.2 (2.88 to 60.3) * 14.8 (3.10 to 70.1) * 3/27 (11.1) 13/136 (9.6) 1.18 (0.31 to 4.47) 1.32 (0.33 to 5.33) Shoulder dystocia 2 (2.2) 3 (2.9) 0.77 (0.13 to 4.69) 0.80 (0.12 to 5.21) 0 (0.0) 5 (3.2) ___ Postnatal admission >3 days 20 (22.5) 12 (11.7) 2.20 (1.01 to 4.80) * 2.36 (1.04 to 5.37) * 9 (25.7) 23 (14.6) 2.02 (0.84 to 4.85) 2.43 (0.97 to 6.10) Neonatal Arterial pH <7.10 5 (5.6) 6 (5.8) 0.96 (0.28 to 3.27) 0.93 (0.27 to 3.23) 3 (8.6) 8 (5.1) 1.75 (0.44 to 6.95) 1.85 (0.45 to 7.57) Neonatal trauma † 7 (7.9) 9 (8.7) 0.89 (0.32 to 2.50) 0.90 (0.31 to 2.59) 2 (5.7) 14 (8.9) 0.62 (0.13 to 2.86) 0.60 (0.13 to 2.83) Neonatal unit admission 8 (9.0) 12 (11.7) 0.75 (0.29 to 1.92) 0.70 (0.27 to 1.83) 1 (2.9) 19 (12.1) 0.22 (0.03 to 1.65) 0.16 (0.02 to 1.32) Procedural Sequential use of instruments 18 (20.2) 12 (11.7) 1.93 (0.87 to 4.25) 1.98 (0.88 to 4.46) 7 (20.0) 23 (14.6) 1.46 (0.57 to 3.73) 1.43 (0.55 to 3.73) More than 3 pulls 10 (11.2) 17 (16.5) 0.64 (0.28 to 1.48) 0.66 (0.28 to 1.55) 5 (14.3) 22 (14.0) 1.02 (0.36 to 2.92) 0.99 (0.34 to 2.88) More than 1 operator 30 (33.7) 17 (16.5) 2.57 (1.30 to 5.08) * 2.32 (1.13 to 4.76) * 12 (34.3) 35 (22.3) 1.82 (0.82 to 4.02) 1.99 (0.84 to 4.72) Caesarean section 24 (27.0) 5 (4.9) 7.24 (2.63 to 19.9) * 7.29 (2.56 to 20.8) * 8 (22.9) 21 (13.4) 1.92 (0.77 to 4.78) 2.45 (0.91 to 6.59) i Odds Ratio calculated for OP compared to OA ii Adjusted for maternal BMI, male infant, birth weight, labour duration, pathological CTG in 1 st stage iii Denominator refers to vaginal births only * p < 0.05 OP occipito-posterior; CI Confidence Interval † Excluding bruising and skin abrasions, including cephalhaematoma, facial nerve palsy, Erb’s palsy, fracture, retinal haemorrhage, intracranial hae Information & Authors Information Version history V1 Version 1 29 May 2025 Copyright This work is licensed under a Non Exclusive No Reuse License. Collection BJOG: An International Journal of Obstetrics and Gynaecology Keywords delivery: assisted vaginal delivery: caesarean section intrapartum care Authors Affiliations Hayes L 0000-0003-1760-1008 The Coombe Hospital View all articles by this author Ramphul M Rotunda Hospital View all articles by this author Deirdre Murphy J 0000-0001-6074-6718 [email protected] Trinity College Dublin Discipline of Obstetrics and Gynaecology View all articles by this author Metrics & Citations Metrics Article Usage 279 views 141 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Hayes L, Ramphul M, Deirdre Murphy J. jabbrv-ltwa-all.ldf jabbrv-ltwa-en.ldf Birth outcomes associated with assisted vaginal birth in an occipito-posterior position: secondary analyses of the Instrumental Delivery & UltraSound randomised controlled trial and cohort study.. Authorea . 29 May 2025. 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