Cumulative live birth rate and perinatal outcomes of blastocyst versus cleavage-stage embryo transfer: A propensity score matching analysis.

Blastocyst transfer has a higher CLBR and a lower multiple pregnancy rate than cleavage-stage embryo transfer in IVF/ICSI cycles in women under 42 years of age with 5 or more oocytes retrieved on the day of oocyte retrieval. There was no difference in perinatal outcomes. We would suggest that these women select a blastocyst transfer strategy.

The influence of blastocyst transfer and cleavage-stage embryo transfer on pregnancy outcomes has always been controversial. On the 1 hand, it was reported that there was no disparity in pregnancy outcomes between fresh blastocyst transfer and cleavage-stage embryo transfer. [ 1 ] On the other hand, some studies have shown that blastocyst transfer may be more advantageous than cleavage-stage embryo transfer in the fresh cycle. [ 2 , 3 ] With the continuous advancement of vitrification technology, the survival rate of frozen blastocysts is equivalent to that of cleavage-stage embryos, [ 4 , 5 ] and the number of frozen-thawed embryo transfers (FET) has significantly increased. [ 6 ] The cumulative live birth rate (CLBR) per oocyte retrieval cycle, which is defined as the percentage of cycles that obtain the first live birth after using all embryos for fresh and subsequent freeze–thaw cycles, has been recommended as a suitable method for reporting the success of in vitro fertilization (IVF)/ intracytoplasmic sperm injection (ICSI). [ 7 ] A previous study suggested that blastocyst transfer did not improve the CLBR. [ 8 ] Nevertheless, other studies have indicated that transfer of vitrified blastocysts leads to a higher CLBR than cleavage-stage embryo transfer. [ 9 , 10 ] Perinatal outcomes after blastocyst transfer are also concerning. Some studies have reported that blastocyst transfer may be associated with adverse perinatal outcomes, including placental complications and preterm birth, compared with cleavage-stage embryo transfer. [ 11 – 13 ] However, other studies have indicated that there may be no differences in the risk of perinatal outcomes. [ 14 – 16 ] Currently, vitrification is used in the cryopreservation of embryos, however, the optimal transfer strategy (blastocyst vs cleavage-stage embryo) remains controversial. Propensity score matching (PSM) was used to eliminate selection bias in this retrospective study, and we aimed to investigate the effects of these 2 transfer strategies on CLBR per oocyte retrieval cycle and perinatal outcomes.

Data curation: Jianfeng Wu. Investigation: Jianfeng Wu, Ning Yang. Software: Jianfeng Wu. Visualization: Jianfeng Wu, Ning Yang. Writing – original draft: Jianfeng Wu. Methodology: Ning Yang. Project administration: Ning Yang. Validation: Ning Yang. Writing – review & editing: Ning Yang.

We conducted a retrospective cohort study to evaluate the clinical data of 683 oocyte retrieval cycles performed by IVF/ICSI between June 2017 and December 2022 at the Reproductive Medicine Center, Lianyungang Maternal and Child Health Hospital. Either cleavage-stage embryo transfer or blastocyst transfer was performed at the patient’s discretion after a detailed discussion with the clinicians. The women were under 42 years of age, with 5 or more oocytes retrieved on the day of oocyte retrieval. Patients with more than 3 IVF/ICSI cycles, chromosomal abnormalities, or endometrial disorders were excluded. There were 418 oocyte retrieval cycles in the cleavage-stage embryo transfer group and 265 cycles in the blastocyst transfer group. After matching the baseline data using PSM, 208 oocyte retrieval cycles were included in both the groups. This study was approved by the ethical committee of Lianyungang Maternal and Child Health Hospital (LYG~MER2021022). The long agonist, antagonist, or microdose flare protocol was used according to the clinician’s preference. When at least 2 follicles reached a mean diameter of 18 mm or 3 follicles reached 17 mm, recombinant human chorionic gonadotropin (HCG) (Ovidrel, Merck-Serono, Magnolia, Italy) 250 μg was given. Oocyte retrieval was performed 36 hours later. Fertilization using IVF or ICSI depends on sperm quality and quantity. The quality of cleavage-stage embryos was assessed using morphological criteria based on cell number, cell fragments, and symmetry of blastomeres. [ 17 ] Blastocyst quality was evaluated using the Gardner grading guide, [ 18 ] according to expansion, inner cell mass, and trophectoderm development. High-quality cleavage embryos or blastocysts were transferred into the uterus, and vitrification was used for cryopreservation of the remaining embryos in both groups. Freezing and thawing of the embryos were performed according to the Vitrification Product Instruction Manual (Kitazato, Japan). FET was performed if the fresh embryo cycle transfer did not result in a live birth. For FET, the natural cycle, hormone replacement cycle, or ovulation induction cycle was performed to prepare the endometrium. [ 19 ] Luteal support with vaginal progesterone soft capsule 200 mg/d and oral dydrogesterone 20 mg/d was initiated on the day of oocyte retrieval. If the patient had a positive β-HCG test on days 12 to 14, ultrasound examinations were performed after 4 to 5 weeks to identify pregnancy, which was defined as an intrauterine living fetus with a heartbeat. If pregnancy was achieved, luteal support was continued for 70 days. Patients were followed up until the birth of their first child. The primary outcome was CLBR. Live birth of twins or multiples were counted as 1 live birth. The secondary outcomes were clinical pregnancy, implantation, live birth, multiple pregnancy, abortion (<28 weeks), ectopic pregnancy, preterm birth (<37 weeks), stillbirth, pregnancy complications, gestational age, birth weight, sex ratio, and birth defects in newborns. Statistical analysis was performed using SPSS software (version 26.0). Continuous variables were analyzed using the Kolmogorov–Smirnov test. Normally distributed data were presented as mean ± standard deviation (SD), and an independent Student t test was used for comparison between the 2 groups. The chi-squared (χ2) test or Fisher’s exact test was used to compare categorical variables. PSM was performed to match the baseline data of the 2 groups in a 1:1 ratio. Logistic regression analysis was used to control for potential confounders and to compare CLBR between the 2 groups. A 2-sided P -value < .05 was utilized as statistical significance.

A total of 683 oocyte retrieval cycles were included in the study, and most of the baseline characteristics were not significantly different between the cleavage-stage embryo transfer group and blastocyst transfer group before PSM, except for estradiol level on the trigger day, number of oocytes retrieved, number of fertilization, and viable cleavage-stage embryos on day 3 (Table 1 ). After PSM, 208 oocyte retrieval cycles were included in the 2 groups respectively and there was no statistically significant difference in baseline variables (Table 1 ). Comparison of baseline characteristics of patients. Data are presented as the mean ± SD or % (positive/total number). AFC = antral follicle count in both ovaries, AMH = anti-Müllerian Hormone, BMI = body mass index, D3 = day 3, FSH = follicle-stimulating hormone, ICSI = intracytoplasmic sperm injection, IVF = in vitro fertilization. P -value <.05. As shown in Table 2 . Compared to the cleavage-stage embryo transfer group in the fresh embryo transfer cycles, the number of embryos transferred in the blastocyst transfer group was lower ( P  < .001), and there was no statistically significant difference in the endometrial thickness and rate of high-quality embryos transferred. No differences in clinical pregnancy rate, abortion rate, ectopic pregnancy rate, and live birth rate were observed between the 2 groups. The implantation rate was higher ( P  = .009), and multiple pregnancy rate was significantly lower ( P  = .049) in the blastocyst transfer group than in the cleavage-stage embryo transfer group. Comparison of clinical outcomes in fresh embryo transfer cycles. Data are presented as the mean ± SD or % (positive/total number). P -value < .05. As shown in Table 3 . In the FET cycles, the cleavage-stage embryo transfer group included 116 cycles and the blastocyst transfer group included 100 cycles. There was no statistically significant difference in the survival rate of embryos, endometrial preparation, endometrial thickness, and the rate of high-quality embryos transferred. The number of embryos transferred in the blastocyst transfer group was lower than that in the cleavage-stage embryo transfer group ( P  < .001). No differences in clinical pregnancy rate, multiple pregnancy rate, abortion rate, and ectopic pregnancy rate were observed between the 2 groups. The clinical pregnancy rate ( P  = .015), implantation rate ( P  < .001), and live birth rate ( P  = .003) were significantly higher in the blastocyst transfer group than in the cleavage-stage embryo transfer group. Comparison of clinical outcomes in frozen embryo transfer cycles. Data are presented as the mean ± SD or % (positive/total number). P -value < .05. Table 4 shows that CLBR was higher ( P  = .034) and multiple pregnancy rate was lower ( P  = .016) in the blastocyst transfer group than in the cleavage-stage embryo transfer group. There was no statistically significant difference between the 2 groups in the monozygotic twin rate, preterm birth rate, stillbirth rate, pregnancy complication rate, sex ratio, gestational age, low birth weight, macrosomia, and birth defects in newborns. Comparison of CLBR and perinatal outcomes. Data are presented as the mean ± SD or % (positive/total number). CLBR = cumulative live birth rate, LBW = low birthweight. P -value <.05. As shown in Table 5 , the univariate logistic regression analysis showed that CLBR was affected by female age, infertility factors, antral follicle count in both ovaries, ovarian stimulation, number of oocytes retrieved, viable cleavage-stage embryos on day 3, high-quality cleavage-stage embryos on day 3, number of frozen embryos, and types of transferred embryos. The other characteristics did not have any effects. Multivariable logistic regression analysis was used to adjust for confounders, and the results showed that the CLBR was positively affected by the number of frozen embryos. Compared to cleavage-stage, blastocyst transfer can improve CLBR. Univariate and multivariable logistic regression analysis of baseline characteristics on CLBR. AFC = Antral follicle count in both ovaries, AMH = Anti-Müllerian Hormone, BMI = Body mass index, D3 = day 3, FSH = Follicle-stimulating hormone, ICSI = intracytoplasmic sperm injection, IVF = in vitro fertilization, OR = odds ratio, Ref = reference category. P -value < .05.

There is an ongoing debate regarding the benefits of blastocyst transfer. A systematic review reported that fresh blastocyst transfer led to a higher clinical pregnancy rate and live birth rate than cleavage-stage embryo transfer. [ 2 ] However, for transfer at a later date, frozen supernumerary embryos were lower in the blastocyst transfer group. Our study indicated that there were no significant differences in clinical pregnancy rate and live birth rate between fresh blastocyst transfer and fresh cleavage-stage embryo transfer. Additionally, there was no significant difference in the number of frozen embryos after fresh embryo transfer. This may be attributed to the advancement of blastocyst culture technology and the lower number of embryos transferred during fresh blastocyst transfer than during fresh cleavage-stage embryo transfer. With the wide application of the vitrification technique, the difference between blastocyst and cleavage-stage embryos in FET is negligible. [ 20 – 22 ] Hence, the CLBR per oocyte retrieval cycle is recommended as a key indicator of treatment success rate. In a previous study, the survival rate of the embryos was approximately 80%. [ 23 ] In contrast, embryo cryopreservation and thawing in this study were conducted using the vitrification technique totally. As a result, the survival rate of the embryos was similar, with > 98% survival in the 2 groups. Furthermore, our study indicated that the clinical pregnancy rate, implantation rate, and live birth rate were higher in the blastocyst transfer group than in the cleavage-stage embryo transfer group in FET cycles. It has been demonstrated that the vitrification procedure can cause zona pellucida hardening, which may decrease fertilization ability. [ 24 ] Nevertheless, laser-assisted hatching during frozen-thawed blastocyst transfer can increase implantation rate, pregnancy rate, and live birth rate. [ 25 ] In this study, all FET cycles were conducted using laser-assisted hatching, which may have contributed to improving CLBR and perinatal outcomes. The effect of different types of transferred embryos (blastocysts vs cleavage-stage embryos) on CLBR is still uncertain. In our study, PSM was performed to match baseline data, and logistic regression analysis was used to control for potential confounders. We found that blastocyst transfer had a higher CLBR than cleavage-stage embryo transfer, which is consistent with the results of other studies. [ 9 , 10 ] Compared to the cleavage-stage embryo transfer group, the number of embryos transferred in the blastocyst transfer group was lower in this study, which contributed to increasing the transplantable cycles of blastocysts that were associated with a significantly higher live birth rate. In a previous study, not all blastocysts were derived from high-quality cleavage-stage embryos. [ 26 ] Compared to blastocysts derived from high-quality cleavage-stage embryos, blastocysts derived from poor-quality cleavage-stage embryos can lead to chromosomal aberrations [ 27 ] and a lower live birth rate. [ 28 ] In our study, only high-quality cleavage-stage embryos were cultured to the blastocyst-stage, which may contribute to improving the CLBR. Perinatal outcomes are also important factors affecting embryo transfer strategies. A retrospective cohort study revealed that in patients receiving assisted reproductive technology, multiple pregnancy rate and adverse obstetric outcomes were common occurrences, that included cesarean delivery, low birthweight, preterm birth, gestational diabetes, postpartum hemorrhage, preeclampsia and eclampsia, dystocia, and postpartum hemorrhage. [ 29 ] Our results indicated that blastocyst transfer resulted in a higher implantation rate and lower multiple pregnancy rate than cleavage-stage embryo transfer. We attributed the lower risk of multiple pregnancy to the lower number of embryos transferred in the blastocyst transfer group. It has been demonstrated that extended culture to the blastocyst-stage for transfer is safe. [ 30 ] Furthermore, extended embryo culture to the blastocyst-stage led to the exposure of embryos to the environment, which is analogous to the natural cycle, and enabled the selection of high-quality blastocysts with a higher implantation potential. [ 31 ] Some previous studies speculated that blastocyst transfer may be associated with the risk of placenta previa, preterm birth, and an altered male/female ratio. [ 13 , 26 , 32 ] However, other studies have not supported these conclusions. [ 12 , 33 , 34 ] Our results suggest that there was no increased risk of perinatal outcomes in the blastocyst transfer group compared with the cleavage-stage embryo transfer group. This study has several limitations. Although PSM was performed to match the baseline data, and logistic regression analysis was used to control for potential confounders, it may not completely avoid the limitations of a single-center retrospective study. In addition, only women under 42 years of age with 5 or more oocytes retrieved on the day of oocyte retrieval were included in this study, which leads to the fact that our results are not applicable to all infertility in women.