Pregnancy: 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 andoutcome of pregnancy in relation to the number of embryos transferredduring in-vitro fertilization (IVF), an analysis was performedof 1060 pregnancies conceived in a tertiary-referral IVF clinic.There was no difference in the miscarriage rate after transferof one or two embryos (37.7% and 34.6%), or after three or fourembryos (22.5% and 25.2%). The miscarriage rate was, however,higher when one or two embryos were transferred compared withthree (P < 0.01) or four embryos (P < 0.02). Of the 724ongoing 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 andquadruplet 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 wassimilar 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 twins80.0/1000 and for triplets 30.6/1000. All of the babies fromthe three quadruplet pregnancies survived. There were more babieslost in the twin pregnancies than any other group, althoughthis only reached significance for singletons versus twins (P< 0.00005). We conclude that the incidence of miscarriageis increased in women in whom one or two embryos are transferred.Multiple pregnancies are more likely to occur in younger womenand are associated with a significantly higher rate of perinatalmortality.