The impact of endometrial preparation for frozen embryo transfer on maternal and neonatal outcomes: a review

The effects of endometrial thickness on outcomes of pregnancy following embryo transfer: A retrospective cohort

OBJECTIVE

The safety of assisted reproductive technology can be assessed by examining birth weight as an outcome measure. The objective of this study was to evaluate the effect of endometrial thickness during embryo transfer on newborn birth weight and preterm labor.

METHODS

We conducted a retrospective cohort study at the infertility department of a teaching hospital affiliated with a university of medical sciences. Eligible women were ≥18 years old and conceived a singleton pregnancy with embryo transfer and an endometrial thickness of ≥7 mm. None of the patients had diabetes, blood hypertension, and polycystic ovarian syndrome. We assessed maternal and newborn characteristics and perinatal pregnancy outcomes.

RESULTS

In total, 100 eligible patients with a mean (SD) age of 32.8 (6.2) years were included. The mean endometrial thickness during embryo transfer was 9.1 (1.2) mm, and the mean birth weight was 3040.7 (565.3)g. There were no statistically significant associations between endometrial thickness and preterm labor (p=0.215) and between endometrial thickness and stillbirth or intra-uterine fetal death (p=0.880). However, after adjusting for confounding factors, the association of endometrial thickness with birth weight was statistically significant [b=124.6 (51.6), p=0.018].

CONCLUSIONS

Within the range of ≥7mm, endometrial thickness during embryo transfer is a predictor of newborn weight; however, it is not related to the risk of preterm labor, stillbirth, or intra-uterine fetal death.

Livebirth rate after one frozen embryo transfer in ovulatory women starting with natural, modified natural, or artificial endometrial preparation in Viet Nam: an open-label randomised controlled trial

BACKGROUND

Use of frozen embryo transfer (FET) in in-vitro fertilisation (IVF) has increased. However, the best endometrial preparation protocol for FET cycles is unclear. We compared natural and modified natural cycle strategies with an artificial cycle strategy for endometrial preparation before FET.

METHODS

In this randomised, open-label study, we recruited ovulatory women aged 18-45 years at a hospital in Ho Chi Minh City, Viet Nam, who were randomly allocated (1:1:1) to natural, modified natural, or artificial cycle endometrial preparation using a computer-generated random list and block randomisation. The trial was not masked due to the nature of the study interventions. In natural cycles, no oestrogen, progesterone, or human chorionic gonadotropin (hCG) was used. In modified natural cycles, hCG was used to trigger ovulation. In artificial cycles, oral oestradiol valerate (8 mg/day from day 2-4 of menstruation) and vaginal progesterone (800 mg/day starting when endometrial thickness was ≥7 mm) were used. Embryos were vitrified, and then one or two day-3 embryos or one day-5 embryo were warmed and transferred under ultrasound guidance. If the first FET cycle was cancelled, subsequent cycles were performed with artificial endometrial preparation. The primary endpoint was livebirth after one FET. This trial is registered at ClinicalTrials.gov, NCT04804020.

FINDINGS

Between March 22, 2021, and March 14, 2023, 4779 women were screened and 1428 were randomly assigned (476 to each group). 99 first FET cycles were cancelled in each of the natural and modified cycle groups, versus none in the artificial cycle group. The livebirth rate after one FET was 174 (37%) of 476 in the natural cycle strategy group, 159 (33%) of 476 in the modified natural cycle strategy group, and 162 (34%) of 476 in the artificial cycle strategy group (relative risk 1·07 [95% CI 0·87-1·33] for natural vs artificial cycle strategy, and 0·98 [0·79-1·22] for modified natural vs artificial cycle strategy). Maternal and neonatal outcomes did not differ significantly between groups, as the power to detect small differences was low.

INTERPRETATION

Although the livebirth rate was similar after natural, modified natural, and artificial cycle endometrial preparation strategies in ovulatory women undergoing FET IVF, no definitive conclusions can be made regarding the comparative safety of the three approaches.

FUNDING

None.

Obstetrical and Neonatal Outcomes of in vitro Fertilization Twins after Fresh Embryo Transfer versus Frozen-Thawed Embryo Transfer

OBJECTIVES

The limited data regarding obstetrical outcomes in multiple pregnancies following both fresh embryo transfer and frozen-thawed embryo transfer (FET), along with the association between multiple pregnancies and increased pregnancy complications compared to singleton pregnancies, highlight the need for research on this topic. Therefore, this study aimed to compare obstetrical and neonatal outcomes of twin pregnancies after fresh embryo transfer versus FET.

DESIGN

This was a retrospective single-center study.

PARTICIPANTS

There were in vitro fertilization (IVF) dichorionic twin pregnancies ≥23 weeks of gestation during 2010-2022.

SETTING

This retrospective study was based on data recorded at Galilee Medical Center, a tertiary-care university-affiliated hospital, Israel.

METHODS

We conducted a comparative analysis of obstetrical and neonatal outcomes between IVF dichorionic twin pregnancies after fresh embryo transfer and those after FET. This analysis included variables such as gestational age at delivery, birthweight, preterm birth rates, low birthweight rates, neonatal intensive care unit admissions, and complications related to prematurity.

RESULTS

The study included 389 IVF twin pregnancies: 253 after fresh embryo transfer and 136 after FET. Following fresh embryo transfer compared to FET, the mean gestational age at delivery was earlier (34 + 6 vs. 35 + 5 weeks, p = 0.001) and the rate of preterm birth (<37 weeks) was higher (70.4% vs. 53.7%, p = 0.001). This difference in gestational age at delivery remained significant after adjustment for maternal age, parity, and BMI (OR = 2.11, 95% CI: 2.11-3.27, p = 0.001). Similarly, the difference in preterm birth rates remained significant after adjustment of the same variables (p = 0.001). For the fresh embryo transfer compared to the FET group, the mean birthweight was lower (2,179.72 vs. 2,353.35 g, p = 0.003); and low birthweight and very low birthweight rates were higher (71.2% vs. 56.3%, p < 0.001 and 13.5% vs. 6.7%, p = 0.004, respectively). For the fresh embryo transfer compared to the FET group, the proportions were higher of neonates admitted to the neonatal intensive care unit (23.3% vs. 16.0%, p = 0.019), of neonates with respiratory distress syndrome (10.5% vs. 5.9%, p = 0.045) and those needing phototherapy (23.3% vs. 16.0%, p = 0.019).

LIMITATIONS

Limitations of the study include its retrospective nature. Furthermore, we were unable to adjust for some confounders, such as the number of eggs retrieved, the number of embryos transferred, and methods for ovarian stimulation or preparation of the endometrium for embryo transfer.

CONCLUSIONS

Obstetrical and neonatal outcomes of twin pregnancies were worse after fresh embryo transfer than after FET. The findings support favorable fetal outcomes after FET and support the current trend of shifting from fresh embryo transfer to FET. Prospective studies are needed to support our results.

Current understanding of the pathogenesis of placenta accreta spectrum disorder with focus on mitochondrial function

AIM

The refinement of assisted reproductive technology, including the development of cryopreservation techniques (vitrification) and ovarian stimulation protocols, makes frozen embryo transfer (FET) an alternative to fresh ET and has contributed to the success of assisted reproductive technology. Compared with fresh ET cycles, FET cycles were associated with better in vitro fertilization outcomes; however, the occurrence of pregnancy-induced hypertension, preeclampsia, and placenta accreta spectrum (PAS) was higher in FET cycles. PAS has been increasing steadily in incidence as a life-threatening condition along with cesarean rates worldwide. In this review, we summarize the current understanding of the pathogenesis of PAS and discuss future research directions.

METHODS

A literature search was performed in the PubMed and Google Scholar databases.

RESULTS

Risk factors associated with PAS incidence include a primary defect of the decidua basalis or scar dehiscence, aberrant vascular remodeling, and abnormally invasive trophoblasts, or a combination thereof. Freezing, thawing, and hormone replacement manipulations have been shown to affect multiple cellular pathways, including cell proliferation, invasion, epithelial-to-mesenchymal transition (EMT), and mitochondrial function. Molecules involved in abnormal migration and EMT of extravillous trophoblast cells are beginning to be identified in PAS placentas. Many of these molecules were also found to be involved in mitochondrial biogenesis and dynamics.

CONCLUSION

The etiology of PAS may be a multifactorial genesis with intrinsic predisposition (e.g., placental abnormalities) and certain environmental factors (e.g., defective decidua) as triggers for its development. A distinctive feature of this review is its focus on the potential factors linking mitochondrial function to PAS development.

Clinical outcomes of frozen-thawed embryo transfer in natural cycles with luteinized unruptured follicles

OBJECTIVE

To assess the effect of luteinized unruptured follicles (LUF) on frozen-thawed embryo transfer cycles performed in natural cycles (FET-NC).

METHODS

Retrospective cohort study, held in a university hospital with 3415 cycles for frozen-thawed embryo transfer, performed between June 2019 and September 2022. Using propensity score matching, 242 patients with a diagnosis of LUF (LUF group) were matched with 484 ovulated patients (ovulation group). Stratified by the type of embryo transferred, the LUF group included 168 blastocyst transfer patients (blastocyst group) and 74 cleavage-stage embryo transfer patients (cleavage-embryo group). The ovulation group included 324 patients with blastocyst transfer (blastocyst group) and 160 patients with transferred cleavage-stage embryos. Clinical pregnancy rate was retrospectively analyzed between the LUF and ovulation groups, as well as between each subgroup.

RESULTS

After using propensity score matching, the general characteristics of the LUF and ovulation groups were similar. The implantation and clinical pregnancy rates in the LUF group were not significantly different from those in the ovulation group (44.98 % vs. 45.29 %, p = 0.93; 53.72 % vs. 52.48 %, p = 0.75). The implantation and pregnancy rates of transferred cleavage-stage embryos in the LUF group were also not significantly different from those in the ovulation group (32.39 % vs. 36.40 %, p = 0.42; 47.30 % vs. 47.50 %, p = 0.98). The implantation and pregnancy rates of transferred blastocysts in the LUF group were also not significantly different from those in the ovulation group (53.11 % vs. 52.03 %, p = 0.82; 56.55 % vs. 54.94 %, p = 0.73). There was also no significant difference in the miscarriage rate between the groups.

CONCLUSION

In the natural cycle, LUF does not affect the clinical pregnancy outcomes of FET. If adequate luteal support is given, the clinical pregnancy outcomes were similar between the LUF group and ovulation group.

Assessing obstetric outcomes: A systematic review and meta-analysis comparing fresh, artificial, and natural thaw embryo transfer cycles

BACKGROUND

The increasing utilisation of in vitro fertilisation (IVF) has prompted significant interest in determining the optimal endometrial environment to increase pregnancy rates and minimise the obstetric complications associated with various embryo transfer strategies.

AIMS

To determine which cycle is associated with increased obstetric complications: fresh embryo transfer (FreshET), natural thaw (NatThawET) or artificial thaw (ArtThawET). Outcomes of interest included: hypertensive disorders of pregnancy (HDP), gestational diabetes (GD), pre-term birth (PTB), post-partum haemorrhage (PPH) and large for gestational age (LGA).

MATERIALS AND METHODS

A comprehensive search of MEDLINE, EMBASE, CENTRAL, and PUBMED was conducted from 1947 to May 17, 2022. Two independent reviewers carried out the screening, and data extraction for the following comparisons: ArtThawET vs NatThawET, ArtThawET vs FreshET, and NatThawET vs FreshET. Meta-analysis was conducted using a fixed-effect Mantel-Haenszel model. The quality of the studies was assessed using GRADEpro.

RESULTS

A total of 23 studies were included in this review. ArtThawET was associated with a significantly increased odds of HDP (odds ratio (OR) 1.76, confidence interval (CI) 1.66-1.86), PTB (OR 1.18, CI 1.13-1.23), PPH (OR 2.61, CI 2.3-2.97) and LGA (OR 1.11, CI 1.07-1.15), compared to NatThawET. ArtThawET was also associated with increased odds of HDP (OR 2.13, CI 1.89-2.4), PPH (OR 3.52, CI 3.06-4.04) and LGA (OR 2.12, CI 1.77-2.56), compared to FreshET. Furthermore, NatThawET demonstrated increased odds of HDP (OR 1.20, CI 1.11-1.29), PPH (OR 1.25, CI 1.14-1.38) and LGA (OR 1.85, CI 1.66-2.07) compared to FreshET.

CONCLUSION

When clinically feasible, ArtThawET should be avoided as a first-line option for IVF to reduce the risk of obstetric complications. An adequately powered, multicentre randomised controlled trial is necessary to confirm these findings and investigate the underlying pathophysiology.

Nutrient deprivation induces mouse embryonic diapause mediated by Gator1 and Tsc2

Embryonic diapause is a special reproductive phenomenon in mammals that helps embryos to survive various harsh stresses. However, the mechanisms of embryonic diapause induced by the maternal environment is still unclear. Here, we uncovered that nutrient deficiency in uterine fluid was essential for the induction of mouse embryonic diapause, shown by a decreased concentration of arginine, leucine, isoleucine, lysine, glucose and lactate in the uterine fluid of mice suffering from maternal starvation or ovariectomy. Moreover, mouse blastocysts cultured in a medium with reduced levels of these six components could mimic diapaused blastocysts. Our mechanistic study indicated that amino acid starvation-dependent Gator1 activation and carbohydrate starvation-dependent Tsc2 activation inhibited mTORC1, leading to induction of embryonic diapause. Our study elucidates the essential environmental factors in diapause induction.

Letrozole During Frozen Embryo Transfer in Women With Polycystic Ovarian Syndrome: A Randomized Controlled Trial

OBJECTIVE

To compare live-birth rates between letrozole application and artificial cycle for endometrium preparation during frozen embryo transfer (FET) cycle among women with polycystic ovarian syndrome (PCOS).

METHODS

A randomized controlled trial was conducted. Women with PCOS were randomized to letrozole application for ovulation induction compared with artificial cycle for endometrial preparation during FET. The primary outcome was live-birth rate per embryo transfer. Secondary outcomes included pregnancy-related outcomes, perinatal outcomes, and maternal complication rates. Assuming α=0.05 and 80% power, 186 patients per group were required to demonstrate a difference of 15% in live-birth rate: 205 patients (at least) per group were randomized to allow for a 10% dropout rate.

RESULTS

Four hundred twenty patients were enrolled from 2018 to 2021. Two hundred ten patients were assigned to the letrozole application group, and 210 were assigned to the artificial cycle group. There was no difference in the live-birth rate (42.4% vs 42.9%, P =>.99). There was no difference in secondary outcomes, including clinical pregnancy rate (51.4% vs 56.2%, P =.378), implantation rate (51.8% vs 55.8%, P =.401), and miscarriage rate (8.6% vs 11.0%, P =.511). For perinatal outcomes, singleton birth weight was significantly higher in the artificial cycle group (3,108±56 g vs 3,301±58, P =.018), and the incidence of gestational diabetes mellitus (GDM) was significantly higher in letrozole application group (14.6% vs 5.6%, P =.050). The other outcome was no difference in maternal complications.

CONCLUSION

There was no difference in pregnancy outcomes between letrozole application compared with artificial cycle for endometrial preparation in women with PCOS who underwent FET. The risk of GDM was higher in the letrozole application group, and the singleton birth weight was lower in the artificial cycle group.

CLINICAL TRIAL REGISTRATION

Chinese Clinical Trial Registry, ChiCTR1800014746.

Elevated Sperm DNA Damage in IVF-ICSI Treatments Is Not Related to Pregnancy Complications and Adverse Neonatal Outcomes

This multicenter retrospective cohort study assesses the effect of high paternal DNA fragmentation on the well-being of the woman during pregnancy and the health of the newborn delivered. It was performed with clinical data from 488 couples who had a delivery of at least one newborn between January 2000 and March 2019 (243 used autologous oocytes and 245 utilized donated oocytes). Couples were categorized according to sperm DNA fragmentation (SDF) level as ≤15% or >15%, measured by TUNEL assay. Pregnancy, delivery, and neonatal outcomes were assessed. In singleton pregnancies from autologous cycles, a higher but non-significant incidence of pre-eclampsia, threatened preterm labor, and premature rupture of membranes was found in pregnant women from the >15%SDF group. Additionally, a higher proportion of children were born with low birth weight, although the difference was not statistically significant. After adjusting for potential confounders, these couples had lower odds of having a female neonate (AOR = 0.35 (0.1-0.9), p = 0.04). Regarding couples using donor's oocytes, pregnancy and neonatal outcomes were comparable between groups, although the incidence of induced vaginal labor was significantly higher in the >15% SDF group (OR = 7.4 (1.2-46.7), p = 0.02). Adjusted analysis revealed no significant association of elevated SDF with adverse events. In multiple deliveries from cycles using both types of oocytes, the obstetric and neonatal outcomes were found to be similar between groups. In conclusion, the presence of an elevated SDF does not contribute to the occurrence of clinically relevant adverse maternal events during pregnancies, nor does it increase the risk of worse neonatal outcomes in newborns. Nevertheless, a higher SDF seems to be related to a higher ratio of male livebirths.

PGT-A improved singleton live birth rate among all age groups of women who underwent elective single blastocyst transfer: a single-centre retrospective study

PURPOSE

This study assessed the difference in singleton live birth rate (SLBR) between preimplantation genetic testing for aneuploidy (PGT-A) and non-PGT in patients undergoing elective single frozen blastocyst transfer (eSFBT).

METHODS

This retrospective cohort study evaluated 10,701 cycles of eSFBT, including PGT-A (n = 3125) and non-PGT (n = 7576). Cycles were further stratified according to age at retrieval. The main outcome was SLBR; secondary outcomes were clinical pregnancy, conception rates, and multiple live birth rate. Confounders were adjusted using multivariable logistic regression models, and the trend test was performed using the general linear model.

RESULTS

SLBR was negatively correlated with age in the non-PGT group (p-trend < 0.001) but not in PGT-A group (p-trend = 0.974). Stratified by the age, SLBR were significantly different between two groups except for the 20-24-year-old group: PGT-A vs non-PGT group in 20-24, 25-29, 30-34, 35-39 and ≥ 40-year-old subgroups were, 53.5% vs 53.2%, 53.5% vs 48.0%, 53.5% vs 43.1%, 53.3% vs 32.5%, and 42.9% vs 17.6%, respectively. In addition, after adjusting for potential confounders, SLBR still remained significantly different in all age groups except in the youngest quartile (PGT-A vs non-PGT group, 20-24: adjusted odds ratio (aOR), 1.33, 95% CI, 0.92-1.92, p = 0.129; 25-29: aOR, 1.32, 95% CI, 1.14-1.52, p < 0.001; 30-34: aOR, 1.91, 95% CI, 1.65-2.20, p < 0.001; 35-39: aOR, 2.50, 95% CI, 1.97-3.17, p < 0.001; ≥ 40: aOR, 3.54, 95% CI, 1.66-7.55, p = 0.001).

CONCLUSION

PGT-A might improve SLBR among all age groups and play an increasingly important role in SLBR in older patients who underwent eSFBT.

Recent Status of Pregnancies at an Advanced Maternal Age at a Japanese Perinatal Center

Objective We compared the recent obstetric outcomes of women aged 40 and over as advanced maternal age (AMA) to those with AMA more than 10 years ago. Methods This was a retrospective study of primiparous singleton pregnancies who delivered at ≥22 weeks of gestation managed at Japanese Red Cross Katsushika Maternity Hospital between 2003-2007 and 2013-2017. Results The percentage of primiparous women aged with AMA who delivered at ≥22 weeks of gestation increased from 1.5 to 4.8% (p<0.01) due to the increase in the pregnancy conceived by in vitro fertilization (IVF). In the pregnancies with AMA, the percentage of cesarean delivery decreased from 51.7 to 41.0% (p=0.01), while the prevalence of postpartum hemorrhage increased from 7.5 to 14.9% (p=0.01). The latter was associated with an increased rate of in vitro fertilization (IVF) use. Conclusions The percentage of AMA pregnancies significantly increased with the development of assisted reproductive technology, and the prevalence of postpartum hemorrhage also increased in AMA pregnancies.

Obstetric and perinatal outcomes following frozen and fresh embryo transfer in patients with endometrial hyperplasia and carcinoma: a retrospective study in a high-volume reproductive center

BACKGROUND

There is ongoing debate regarding which embryo transfer procedure can achieve a higher live birth rate. Research has suggested that frozen ET might be beneficial for certain populations, such as hyper-responders. This study aimed to compare outcomes of pregnancies between frozen and fresh embryo transfer cycles in patients with endometrial hyperplasia and carcinoma.

METHODS

This retrospective cohort study was conducted at a high-volume reproductive center from January 2010 to January 2022. Patients who were diagnosed with endometrial hyperplasia with atypia and endometrial carcinoma were included. They all underwent in vitro fertilization after conservative treatment. The primary outcome was live birth after frozen and fresh embryo transfer cycles, and secondary outcomes included perinatal complications and other pregnancy outcomes.

RESULTS

Overall, 259 ET cycles (130 fresh and 129 frozen) were included. The rate of live births per embryo transfer cycle of the whole cohort was 20.8% (54/259), and no significant between-group difference was found after adjusting for potential confounding factors (23.8% vs. 17.8%; adjusted OR, 0.47; 95% CI, 0.21-1.06; p=0.068). Compared to fresh embryo transfer group, the incidence of total maternal complications in the frozen embryo transfer group was significantly higher (30.4% vs. 6.5%, p=0.019). Analyzing each complication as a separate entity, patients in the frozen embryo transfer group had a higher incidence of hypertensive disorders of pregnancy (p=0.028). Multiple logistic regression analysis showed that frozen embryo transfer was related with an increased occurrence of maternal complications (OR, 6.68, 95% CI, 1.01-44.19, p=0.040).

CONCLUSIONS

Among patients with endometrial hyperplasia and carcinoma, the rate of live births was comparable between both embryo transfer procedures, while frozen embryo transfer might be associated with a higher risk of maternal complications compared to that with fresh embryo transfer.

Risk Factors of Preterm Birth and Low Birth Weight in Singletons Conceived Through Frozen Embryo Transfer: A Retrospective Study

Background

The risks of adverse perinatal outcomes in offspring conceived following frozen-thawed embryo transfer (FET) assisted reproductive technology (ART) are inconsistent. The aim of this study was to analyze the risk factors for preterm birth and low birth weight in singletons after FET.

Methods

386 FET cycles was conducted at the Reproductive Medicine Center of Meizhou People's Hospital. The relationship between clinical characteristics and outcomes (term birth and preterm birth, normal birth weight and low birth weight) was analyzed.

Results

The rate of primary infertility, basal FSH and T levels, gestational age, birth weight, and proportion of male fetuses were significantly different in the preterm and full-term groups. Logistic regression analysis showed that high maternal age (≥35 years) (OR 3.652, 95% CI: 1.683-7.925, P=0.001), primary infertility (OR 2.869, 95% CI: 1.461-5.632, P=0.002), low FSH level (<6.215 mIU/mL) (OR 3.272, 95% CI: 1.743-6.144, P<0.001), and hormone replacement therapy (HRT) method (OR 2.780, 95% CI: 1.088-7.100, P=0.033) may increase risk of preterm birth after FET. Gestational age and birth weight were significantly different in fetuses with low birth weight (<2500g, n=38) and normal birth weight (≥2500g and <4000g, n=333). Logistic regression analysis showed that low basal FSH level (<6.215 mIU/mL) (OR 0.425, 95% CI: 0.209-0.865, P=0.018), and HRT method of endometrial preparation for FET (OR 0.272, 95% CI: 0.079-0.934, P=0.039) may reduce the risk of low birth weight after FET.

Conclusion

High maternal age, primary infertility, low FSH level, HRT method of endometrial preparation for FET, and male fetus may increase risk of preterm birth after FET. In addition, primary infertility, low basal FSH level, and HRT method of endometrial preparation may reduce the risk of low birth weight after FET.

Endometrial thickness is associated with low birthweight in frozen embryo transfer cycles: A retrospective cohort study of 8,235 singleton newborns

OBJECTIVE

To explore the association between endometrial thickness (EMT) and adverse neonatal outcomes in frozen in vitro fertilization/intracytoplasmic sperm injection-embryo transfer (IVF/ICSI-ET) cycles.

METHODS

This retrospective study involved a total of 8,235 women under the age of 35 years who underwent IVF/ICSI cycles and received frozen embryo transfer (FET) at a tertiary-care academic medical from January 2015 to December 2019, resulting in a live singleton newborn. Patients were categorized into three groups depending on EMT: ≤7.5 mm, 7.5-12 mm and >12 mm. The primary outcome was low birthweight (LBW). The secondary outcomes were preterm birth (PTB), small-for-gestational age (SGA), large-for-gestational age (LGA) and high birthweight (HBW).

RESULTS

Compared with EMT >7.5-12 mm group, the risk of being born LBW was statistically significantly increased in the EMT ≤7.5 mm group (adjusted odds ratio [aOR] 2.179; 95% confidence interval [CI], 1.305-3.640; P=.003), while dramatically decreased in the EMT >12 mm group (aOR 0.584; 95% CI, 0.403-0.844; P=.004). Moreover, newborn gender and pregnancy complications were all independent predictors for LBW. Furthermore, a significant decrease in birthweight was found in the EMT ≤7.5 mm group as compared with EMT >7.5-12 mm group and EMT >12 mm group (3,239 ± 612 vs. 3,357 ± 512 and 3,374 ± 479 g, respectively), and similar result was found in term of gestational age (38.41 ± 2.19 vs. 39.01 ± 1.68 and 39.09 ± 1.5 weeks, respectively).

CONCLUSIONS

After frozen IVF/ICSI-ET, EMT ≤7.5 mm is independently associated with increased risk of LBW among women with singleton newborns. Therefore, we suggest that women with EMT ≤7.5 mm after achieving pregnancy by IVF/ICSI-ET treatment should warrant more attention to reduce the risk of delivering a LBW newborn.