Single embryo transfer yields fewer pregnancies but more term births

Single embryo transfers are significantly more likely than double embryo transfers to result in a term singleton birth although they produce fewer pregnancies, investigators from the University of Aberdeen, United Kingdom, report.

Their meta-analysis compares live birth, multiple live birth, miscarriage, preterm birth, term singleton birth, and low birth weight outcomes by reviewing data from studies that randomized 1,367 women to a single or double embryo transfer. Odds for a term singleton birth were nearly 5 times higher for single embryo transfer than for double embryo transfer.

The authors note that although single embryo transfer yields a lower pregnancy rate than double embryo transfer in a fresh in vitro fertilization cycle, “this difference is almost completely overcome by an additional frozen single embryo transfer cycle.”

Overall live-birth rates for fresh single embryo transfers were 27% compared with 42% for double embryo transfers. Multiple-birth rates were 2% and 29%, respectively. When a frozen single embryo transfer was performed after the fresh single embryo transfer, the cumulative live-birth rate increased to 38% with minimal cumulative risk of multiple births.

“After an additional fresh or frozen cycle, there is no significant difference in live birth rate between elective single and double embryo transfer and the risk of a multiple birth in the elective single embryo transfer group is still much lower than in the double embryo transfer group,” the authors observe. The multiple pregnancy rate after elective single embryo transfer is comparable to the rate for spontaneous pregnancies.

The study was published in the British Medical Journal (2010;341:c6945).