First trimester bleeding in clinical IVF pregnancies.

First trimester bleeding has been investigated in 72 pregnant women undergoing in-vitro fertilization and embryo transfer and was compared to 70 pregnant patients in whom ovulation was induced, in addition to 70 spontaneous pregnancies. Abortion rates did not differ significantly between the first two groups but were significantly higher in comparison to normal pregnancies. Furthermore, among IVF pregnancies that continued, a high incidence of first trimester bleeding occurred (P less than 0.01). This complication was mainly related to luteal insufficiency and multiple pregnancies, whereas hyperstimulation was the major risk factor for bleeding in pregnancies arising from HMG-induced ovulation. Other currently unknown, aetiological factors for first trimester bleeding in IVF pregnancies remain to be investigated.