{"paper_id":"67337134-18d7-41de-abb8-7f081742c17d","body_text":"Historically, multiple embryos have been transferred in  in vitro \nfertilization (IVF) cycles, in an attempt to compensate for the low implantation\nrates and increase the success of treatment. However, this approach increases the\nlikelihood of multiple pregnancies, which is the main complication of IVF. The\npublication of clinical guidelines on the number of embryos to transfer and\nindications of a reduction in the number of embryos transferred ( Harbottle  et al ., 2015 ;  ASRM/SART, 2017 ) prompted a decrease in the\ntransfer of three or more embryos, and increase in the transfer of one or two\nembryos, but the double embryo transfer is the most common practice yet ( Kissin  et al ., 2015 ).\nIdeally, the goal of assisted reproduction techniques (ART) is to achieve a singleton\ngestation, and a single embryo transfer (SET) is the most effective tool for it\n( ESHRE Guideline Group on Good Practice in IVF,\n2016 ;  ASRM/SART, 2017 ). On the\nother hand, low twinning risk is reduced at the expense of declining pregnancy rates\nin the first cycle, and a need for more embryo transfers to get the same success\nrate, a potential delay in treatment success, potentially higher treatment costs,\ntogether with patient's autonomy to choose placement of more than one embryo tend to\nresult in double embryo transfers done more often ( Gleicher & Barad, 2006 ). Thus, the wide application of SET raises\nquestions, as there is no clear evidence for whom SET should be used. The American\nSociety for Reproductive Medicine encourages individual programs to use their own\ndata regarding patients’ characteristics and the number of embryos transferred,\naiming to maintain pregnancy rates and minimizing multiple pregnancies ( ASRM/SART, 2017 ).\nGood prognosis patients are more indicated to receive SET with satisfactory clinical\noutcomes, such as those under the age of 38 and patients at any age transferring an\neuploid embryo evaluated by preimplantational genetic test for aneuploidy (PGT-A)\n( ASRM/SART, 2017 ). A previous study\ndemonstrated that elective SET employed in women younger than 38 years of age in\nU.S. clinics have decreased multiple pregnancy rates with no impact on cumulative\nlive-birth rates ( Mancuso  et al .,\n2016 ). Our group demonstrated that the accumulated outcome of two\nsequential SET is similar to DET in good prognosis patients ( Monteleone  et al ., 2018 ), and the transfer of\ntwo embryos after a SET failure did not have advantages compared to a second SET\n( Monteleone  et al .,\n2016 ). In addition, the single euploid blastocyst transfer prompts the same\nclinical outcome of two untested blastocysts, while reducing the risk of multiple\npregnancies in women of 42 years or younger ( Forman\n et al ., 2013 ). Apart from those characteristics,\nexpectation of one or more high quality embryos available for cryopreservation, or\nthe availability of vitrified high-quality blastocysts for frozen-thawed transfers\nare also favorable criteria to SET ( Richter et al.,\n2016 ).\nThe exact profile of women who are favorable to receive a SET is not well defined, we\naimed to evaluate the clinical outcomes of IVF cycles for women who had vitrified\nembryos and were undergoing frozen-thawed SET because of infertility factors.\n\nThis is a preliminary retrospective cohort study evaluating 305 frozen-thawed SET\ncycles performed in the last 10 years in a private IVF center in Brazil. All\nprocedures in this study are part of the routine care in the assisted reproductive\ncenter, and written informed consent was obtained from all patients before\ntreatment. Patients consented to the treatment procedures and to the retrospective\ndata used in the scientific publications.\nThe database included 1449 frozen-thawed cycles between 2008 and 2017, which were\npotentially eligible for this study. Then, we deemed eligible for this study if the\npatient received a frozen-thawed SET. We excluded cycles in which testicular or\nepididymal sperm were used. The final number of cycles included and analyzed in our\nstudy was 305 frozen-thawed SET.\nThe patients underwent routine ovarian stimulation and oocyte pickup according to the\nmedical criteria for such. The oocytes were fertilized by ICSI, using ejaculated\nsperm, with or without a fresh embryo transfer according with clinical conditions.\nExtra embryos for patients who received a fresh transfer, or all embryos for\npatients who did not receive a fresh transfer, were vitrified for future\nfrozen-thawed transfers. For the frozen-thawed embryo transfers, endometrial\npreparation was conducted with 100 µg of estradiol valerate (Estradot,\nNovartis, Switzerland) for 14 days plus 600 µg of vaginal micronized\nprogesterone (Utrogestan, Farmoquimica, Brazil) 5 days before the transfer. The\nembryos were warmed, evaluated for survival and morphology, and transferred at a\nblastocyst stage 5 days after progesterone was started. The embryo survival rate\nafter warming was 88.1% and a top-quality blastocyst was preferentially transferred\nwhen available.\nFrozen-thawed transfers were categorized according to the infertility factor by using\nthe classification established by the Society for Assisted Reproductive Technologies\n(SART), such as anatomic female factor (n=55), endocrine female factor (n=26),\nendometriosis (n=37), male factor (n=60), ovarian insufficiency (n=26), unexplained\n(n=24), multiple factors (n=45) and other (n=32).\nData was obtained from a clinical report form and plotted for this study.\nClinical pregnancy was defined by the presence of a gestational sac with a\nheartbeat 2 weeks after confirmation of a biochemical pregnancy (serum beta-hCG\nmeasurement). The clinical pregnancy rate was calculated as the number of\npatients presenting a clinical pregnancy divided by the number of patients with\nembryos transferred.\nAnalyses were performed using the SPSS V.18 (IBM SPSS Software, USA). The patient\ndemographic data were evaluated using descriptive statistics, which included\ninformation on the means, standard deviations and frequencies. The ANOVA was\nused to compare continuous variables, and the Pearson’s chi-squared of Fisher\nexact test were used to compare frequencies as appropriated. Regression analyses\nwere used to evaluate the association between the variables, and a multivariate\nlogistic regression analysis was performed to evaluate the association of each\ninfertility factor and clinical pregnancy rate (CPR) adjusted for confounders.\nThe results were reported as odds ratios and  p -values. We\nconsidered  p -values ≤0.05 to be statistically\nsignificant.\n\nAs for the patients included in the study, 135 had a fresh embryo transfer with no\npregnancy and the second frozen-thawed SET was evaluated in this study. One-hundred\nand fourteen had all embryos cryopreserved and the first frozen-thawed SET was\nevaluated.  Table 1  describes the demographic\ncharacteristics of the patients included in the study.\nDemographic characteristics of patients included in the study\nThe women’s characteristics according to infertility factors are presented on  Table 2 . As expected, the women classified at\novarian insufficiency category are older than the others with higher basal FSH, had\nlower numbers of MII oocytes collected and embryos cryopreserved. Except those, the\nother characteristics were similar between the groups.\nDemographic characteristics of patients included in the study according to\ninfertility factors\nCPR after a frozen-thawed SET for each infertility factor is demonstrated in  Figure 1 . The CPR for patients with different\ninfertility factors seem to be satisfactory for a SET, except for the unexplained\ninfertility that had a very low CPR.\nFigure 1 Clinical pregnancy rates according to infertility factor in Frozen-thawed\nsingle embryo transfers\nClinical pregnancy rates according to infertility factor in Frozen-thawed\nsingle embryo transfers\nA multivariate logistic regression model was built and adjusted for following\nconfounders based on differences found in univariate analysis (women age and number\nof embryos cryopreserved) and conditions that could cause biases to the outcomes as\nif embryos had been evaluated by preimplantational genetic test for aneuploidy or\nnot, and if the patient had a previous fresh embryo transfer or had all embryos\ncryopreserved. The outcomes did not show any significant association between CPR and\ninfertility factors, such as: anatomic female factor (OR: 1.4;\n p =0.409), endocrine female factor (OR: 1.4;\n p =0.509), endometriosis (OR: 1.7;  p =0.254), male\nfactor (OR: 1.0;  p =0.910), ovarian insufficiency (OR: 0.7;\n p =0.720), unexplained (OR: 0.2;  p =0.117),\nmultiple factors (OR: 0.7;  p =0.526) and other (OR: 0.7;\n p =0.597). We can note that despite being non-significant, the\nOR value suggests a decreased likelihood of clinical pregnancy when unexplained\ninfertility is present, adjusted for confounder factors.\n\nIVF success is defined as a singleton pregnancy resulting in a healthy singleton baby\nborn at term ( Min  et al .,\n2004 ). While studies have demonstrated for more than a decade that the\nmost effective tool for prevention of twin pregnancies after IVF is SET, and that\nthe cumulative outcomes have comparable live birth rates and diminished multiple\ngestations (ESHRE Campus Course Report, 2001;  Luke\n et al ., 2015 ;  ASRM/SART, 2017 ;  Monteleone  et\nal.,  2018 ), there still is some resistance to using SET in\ngeneral, and questions regarding in which patient it would be most effective ( van Peperstraten  et al .,\n2008 ). This preliminary study evaluated frozen-thawed SET for women\npresenting different infertility factors and demonstrated a tendency of unexplained\ninfertility has the worst clinical outcomes.\nLuke  et al . (2015)  developed a\nstudy comparing SET and DET, and evaluated the outcomes according to four\ninfertility factors (male factor, ovulation disorder, diminished ovarian reserve and\nunexplained) and found no differences.  Luke\n et al . (2015)  included a higher number of patients\ncompared to our preliminary study and evaluated fresh cycles, finding no\ndifferences, while we had a tendency to have lower CPR in unexplained infertility of\nfrozen-thawed transfers.\nDifferences in study design can justify diverse outcomes. Moreover, our study was\nconducted in an unselected group of patients (i.e. irrespective of the woman’s age\nor embryo quality) but patients included were those who had cryopreserved embryos\nand were undergoing a frozen-thawed ET, which is a favorable condition for SET.\nSelecting couples suitable for SET is an essential step for the success of the\ntechnique. Unexplained infertility is a particular situation in which we do not know\nthe real infertility factor and a number of conditions can be associated, as\nendometrial dysfunction ( Dorostghoal  et\nal ., 2018 ;  Petousis\n et al ., 2018 ) and autoimmunity ( Motak-Pochrzest & Malinowski, 2018 ). We\nobserved a numerically lower CPR for women presenting unexplained infertility, for\nthat, patients should be extensively evaluated in order to determine the factor\nassociated to infertility and correct it before performing an IVF cycle with\nSET.\nThis is a preliminary retrospective study with a small number of cycles in each\ncategory, and the outcomes did not show statistical significance. Hence, the\nfindings should be interpreted with caution. On the other hand, the CPR indicates\nimportant differences in the subgroup of unexplained infertility and this profile of\npatients may not be suitable for SET. We built a regression model considering\nconfounding variables as the woman’s age and the number of embryos cryopreserved,\npreimplantational genetic test for aneuploidy and whether the patient had a previous\nembryo transfer, since those are conditions that establish a good prognosis for a\npatient, and we had the same outcomes even after adjustments. The subgroup of\nunexplained infertility had a very low OR, indicating lower pregnancy likelihood,\nalthough not significant. These findings can be considered in the clinical routine\nwhen indicating an SET cycle, especially when the patients do not have a known\ninfertility factor.\nIn short, our study suggests that for couples presenting unexplained infertility,\neven when a patient has a good prognosis (age lower than 38, preimplantational\ngenetic test for aneuploidy, extra embryos cryopreserved), SET should be considered\nwith caution since the outcomes may be not satisfactory.","source_license":"CC0","license_restricted":false}