The influence of the number of embryos transferred in 1060 in-vitro fertilization pregnancies on miscarriage rates and pregnancy outcome.

To assess the incidence of miscarriage, multiple pregnancy and outcome of pregnancy in relation to the number of embryos transferred during in-vitro fertilization (IVF), an analysis was performed of 1060 pregnancies conceived in a tertiary-referral IVF clinic. There was no difference in the miscarriage rate after transfer of one or two embryos (37.7% and 34.6%), or after three or four embryos (22.5% and 25.2%). The miscarriage rate was, however, higher when one or two embryos were transferred compared with three (P < 0.01) or four embryos (P < 0.02). Of the 724 ongoing pregnancies, 524 (72.3%) were singleton, 164 (22.7%) twin, 33 (4.6%) triplet and three (0.4%) quadruplet. The mean (+/- SD) ages of women with singleton, twin, triplet and quadruplet pregnancies were 32.5 (+/- 3.8), 32.0 (+/- 3.5), 29.76 (+/- 4.3) and 29.67 (+/- 2.5) years respectively. The mean age of women with singleton and twin pregnancies was similar and both were greater than that of triplet pregnancies (P < 0.007). The overall perinatal mortality rate (PNMR) was 39.7/1000. The PNMR for singletons was 17.2/1000, for twins 80.0/1000 and for triplets 30.6/1000. All of the babies from the three quadruplet pregnancies survived. There were more babies lost in the twin pregnancies than any other group, although this only reached significance for singletons versus twins (P < 0.00005). We conclude that the incidence of miscarriage is increased in women in whom one or two embryos are transferred. Multiple pregnancies are more likely to occur in younger women and are associated with a significantly higher rate of perinatal mortality.