Impact of single embryo transfer on the overall and twin-pregnancy rates of an IVF/ICSI programme

This retrospective cohort study analyses experience with single embryo transfer (SET) in an lVF/intracytoplasmic sperm injection (ICSI) programme over a 3-year period (1998-2000): 1143 IVF/ICSI cycles were initiated, resulting in 1073 embryo transfers (93.9%). In 810 (75.4%) transfers of two (n = 580; 54%) or more than two (n = 230; 21.4%) embryos, 279 ongoing pregnancies (34.4%) were obtained. In total, there were 263 SET (24.5%): 207 of a single top quality embryo, resulting in 102 conceptions (49.3%) with 71 ongoing implantations (34.3%, one monozygotic twin); and 56 of a single non-top quality embryo, resulting in 16 conceptions (28.6%) with 11 ongoing implantations (19 .6% ). The percentage of transfers of a single top quality embryo gradually increased from 10% (1998) to 19% (1999) to 26% (2000). The total multiple pregnancy rate decreased from 34% (1998), to 32% ( 1999) and 22% (2000), without affecting the overall ongoing pregnancy rate per transfer: 38% in 1998; 29% in 1999; and 34% in 2000. The average number of transferred embryos decreased from 2.26 ( 1998) to 1.86 (2000). Transfer of a single, strictly defined top quality day 3 embryo in twin-prone IVF/ICSI patients reduced the multiple/twin-pregnancy rate but not the overall pregnancy rate.