BACKGROUND Maternal and fetal complications in pregnancies after renal transplantation have been highlighted in several reports, but information on their main predisposing factors is limited. The U.K. Transplant Pregnancy Registry was established in 1997 to obtain detailed information on pregnancies in female organ transplant recipients across the U.K. METHODS For each female kidney, liver, or cardiothoracic organ transplant recipient who had had a recent pregnancy, data on maternal and fetal factors and pregnancy outcomes were collected using forms completed by their transplant follow-up and obstetric units. For kidney transplant recipients, the factors that influence pregnancy outcome were studied using logistic regression, and the effect of pregnancy on graft function was analyzed. RESULTS There were live births in 83%, 69%, and 79% of pregnancies in cardiothoracic organ, liver, and kidney recipients, respectively. In 50% of live births from renal patients, delivery was preterm (<37 weeks), with 83% of the preterm infants delivered via caesarean. Preterm delivery was associated with maternal drug-treated hypertension and impaired renal function. A matched case-control study showed no evidence of increased renal allograft loss after pregnancy. A univariate survival analysis, however, suggested an association between drug-treated hypertension during pregnancy and poorer postpregnancy graft survival. In patients with prepregnancy serum creatinine (SCr) >150 micromol/L, a trend toward increased postpregnancy SCr was identified. CONCLUSIONS Pregnancy is likely to end in a live birth in a majority of organ transplant recipients. In patients with greater prepregnancy SCr and/or drug-treated hypertension during pregnancy, however, subsequent renal function may be adversely affected.