Equivalency of In vitro fertilization Success Rates in Elective Single Blastocyst Transfer and Elective Double Blastocyst Transfer: An Example of Equivalence Methodology in Clinical Reproductive Health

Comparison of frozen-thaw blastocyst transfer strategies in women aged 35-40 years: a retrospective study

Objective

To compare the effects of five different frozen-thaw embryo transfer (FET) strategies in women aged 35-40 years.

Methods

Data from 1,060 patients were divided into five groups according to the number and quality of transferred blastocysts: a high-quality single blastocyst group (group A, n= 303), a high-quality double blastocysts group (group B, n= 176), a high-quality plus poor-quality double blastocysts group (group C, n= 273), a poor-quality double blastocysts group (group D, n= 189), and a poor-quality single blastocyst group (group E, n= 119). Comparative analyses were then performed between groups with regard to primary conditions, pregnancy, and neonatal outcomes.

Results

Group A had the lowest twin pregnancy rate (1.97%) and incidence of low-birth-weight infants (3.45%), which were significantly different from groups B, C, and D. In addition, the preterm birth rate (7.89%), neonatal birth weight (3300 g [3000, 3637.5]), and neonatal birth age (39.14 weeks [38.43, 39.61]) in group A were different from those in groups B and C. Double blastocyst transfer (DBT) was associated with a 20.558-fold (Risk Ratio [RR]=20.558, 95% confidence interval [CI], 6.628-63.763) and 3.091-fold (RR=3.091, 95% CI, 1.69-5.653) increased risk of twin pregnancy and preterm delivery in unadjusted analysis, respectively, when compared with single blastocyst transfer (SBT). In the adjusted analysis, we observed similar risk estimates (adjusted RR=26.501, 95% CI, 8.503-82.592; adjusted RR=3.586, 95% CI, 1.899-6.769).

Conclusion

Although, high-quality SBT resulted in a lower live birth rate than high-quality DBT, it also significantly reduced the risk of adverse pregnancies, thus resulting in more benefits for both the mother and baby. Collectively, our data indicate that high-quality SBT remains the optimal FET strategy for women aged 35-40 years and warrants further clinical application.

Comparison of frozen-thawed embryo transfer strategies for the treatment of infertility in young women: a retrospective study

Objective

To investigate transfer strategies in the frozen-thawed embryo transfer (FET) cycle.

Methods

The clinical data of 1,652 FET patients were divided into five groups according to the number and quality of the transferred blastocyst: high-quality single blastocyst group (group A, n = 558), high-quality plus poor-quality double blastocyst group (group B, n = 435), poor-quality double blastocyst group (group C, n = 241), high-quality double blastocyst group (group D, n = 298), and poor-quality single blastocyst group (group E, n = 120). Inter-group comparison analyses of primary conditions, pregnancy outcomes and neonatal outcomes were then performed.

Results

Group A had the highest embryo implantation rate (67.38%), significantly different from the implantation rates of the other four groups. The gemellary pregnancy rate (1.60%), preterm birth rate (5.58%), neonatal birth weight (3,350g [3,000g, 3,650g]), neonatal birth age (39.57 weeks [38.71, 40.34]), and incidence of low birth weight (7.02%) in group A were different from those in groups B, C, and D, but did not significantly differ from those in group E. Moreover, the proportions of male infants born in groups A (56.86%) and D (59.41%) were significantly higher than those in the other three groups. Double blastocyst transfer (0.528, 95% CI [0.410-0.680], P < 0.001) and high-quality blastocyst transfer (0.609, 95% CI [0.453-0.820], P = 0.001) were found to be protective factors for live birth. In addition, double blastocyst transfer was also the largest risk factor for pregnancy complications (3.120, 95% CI [2.323-4.190], P < 0.001) and neonatal complications (2.230, 95% CI [1.515-3.280], P < 0.001), especially for gemellary pregnancy (59.933, 95% CI [27.298-131.58], P < 0.001) and preterm birth (3.840, 95% CI [2.272-6.489], P < 0.001). Based on the ROC curves, a double blastocyst transfer could predict gemellary pregnancy reliably with a high area under the curve (AUC = 78.53%). Additionally, a double blastocyst transfer could effectively predict a high risk of pregnancy complications (AUC = 65.90%), neonatal complications (AUC = 64.80%) and preterm birth (AUC = 66.20%).

Conclusion

The live birth rate of frozen-thawed high-quality single blastocyst transfer is lower than that of double high-quality blastocyst transfer, which can significantly increase the embryo implantation rate. High-quality single blastocyst transfer also significantly lowers the risk of gemellary pregnancy, preterm birth, and low birth weight, and can significantly improve maternal and infant outcomes. After weighing the pros and cons of live birth with pregnancy and neonatal complications, the authors believe that high-quality single blastocyst transfer is the optimal FET strategy for young women and is worthy of further clinical application. Despite this recommendation, high-quality single blastocyst transfer can increase the risk of monozygotic twins, as well as significantly increase the proportion of male infants born.

Choosing the optimal blastocyst by morphology score versus developmental rate in frozen-thawed embryo transfer cycles

The aim of this study was to provide guidance for better management in the selection of blastocyst to warm in frozen-thawed embryo transfer (FET) cycles. A retrospective cohort follow-up study was conducted that included single autologous frozen blastocyst transfer cycles performed in our Reproductive Medicine Unit from January 2009 to December 2016. The live birth rate (LBR), clinical pregnancy rate (cPR) were increased as blastocyst morphology scores increased, but the miscarriage rate decreased in all groups. In the high-score groups, there were no differences in LBR between D5 and D6, while in the low-score groups, LBR was significantly higher in D5 compared to the D6. With respect to neonatal outcome, there were no differences in all the groups. After binary logistic regression analysis, it was seen that patients' age, thawed cycles, pre-frozen morphology score and developmental rate were independently associated with LBR. These results suggest that for high-scoring blastocyst, the pre-frozen morphological score should be given priority while for low-scoring blastocysts, the developmental rate should be given priority when thawing in FET cycles.