High incidence of preterm births and early losses in pregnancy after in vitro fertilisation. Australian in vitro fertilisation collaborative group.

A fertilisation cohort of 244 pregnancies resulting from in vitro fertilisation was reported to a national register by eight units specialising in in vitro fertilisation. Early pregnancy losses were high, with 5% tubal ectopic pregnancies, 18% biochemical pregnancies, and an incidence of spontaneous abortion of 27%. Among pregnancies of at least 20 weeks' gestation 22% were multiple, with 26 pairs of twins and four sets of triplets. The incidence of preterm births was more than three times higher than in the general population. Low birthweight rates were also higher, owing both to preterm births and to multiple pregnancies. The sex ratio and the incidence of major congenital malformations were similar to those in naturally conceived pregnancies. In this series the high fetal losses at all stages of pregnancy suggested maternal reproductive causes and should not be interpreted as being due to factors peculiar to in vitro fertilisation. Further analysis will be necessary when larger numbers are available.