Evaluating the effectiveness and safety of two consecutive cycles of single embryo transfer versus one cycle of double embryo transfer in infertile women.

This study evaluated the effectiveness and safety of two consecutive cycles of single embryo transfer (SET) versus one cycle of double embryo transfer (DET) in infertile women. The data showed that two consecutive cycles of SET significantly reduced the rate of multiple births, improved the maternal and neonatal side effects, and showed a similar live birth rate compared to the DET strategy. 

After in vitro fertilization (IVF), embryos are transferred to the uterus. In some cases, only one embryo is transferred (ET). This is called single embryo transfer (SET). In some practices, multiple embryos are transferred to improve the chances of implantation and live birth. When two embryos are transferred, it is called double embryo transfer (DET). This can also lead to multiple pregnancies.

SET is becoming more popular to minimize multiple pregnancies. However, there is still concern it may reduce the success of fertility treatment. The success of IVF and ET is determined by the live birth rate. If multiple embryos are transferred there is a greater chance of implantation. However, the effectiveness and safety of two consecutive cycles of SET versus a single cycle of DET in infertile women are still unknown.

This study analyzed 12 studies and involved a total of 198,892 infertile women. Patients were divided into 2 groups. Group 1 included 40,709 women who underwent two consecutive cycles of SET. Group 2 included 158,183 women who underwent one cycle of DET.

The overall cumulative live birth rate was similar between the two groups (48.24% in group 1 and 48.91% in group 2).

The cumulative multiple birth rate was significantly lower in group 1 (0.87%) versus group 2 (17.72%).

Two consecutive cycles of SET were associated with a lower risk of cesarean section, antepartum hemorrhage (bleeding from the genital tract in the second half of pregnancy), preterm birth (baby born too early), low birth weight of the baby, and neonatal intensive care unit admission. It was also associated with a higher gestational age at birth and birth weight compared to DET.

This study concluded that two consecutive cycles of SET significantly reduced the multiple birth rate, improved the maternal and neonatal side effects, and showed a similar live birth rate compared to the DET strategy. The authors suggested that infertile women aged less than 35 years and receiving blastocyst transfers might benefit more from two cycles of SET strategy.

The sample size was very small. This study did not evaluate the impact of male factor, ovarian reserve or response, and maternal body mass index (BMI; a measure of weight in relation to height) on the outcomes. Larger studies are needed to validate the findings.