*Purpose: Pregnancies after renal transplantation became more frequent over the past years, also in patients with compromised renal function. Immunosuppression may influence pregnancy outcome. It is not yet clear whether replacing a calcineurin inhibitor (CNI) by azathioprine favourably influences pregnancy- or neonatal outcomes. We therefore compared both maternal and fetal outcomes of pregnancies in women with a renal trans­plant using CNI-based or CNI-free immunosuppression.

*Methods: In female renal transplant patients, we retrospectively analyzed outcomes of all pregnancies in the Netherlands between 1986-2017. We collected data on maternal and neonatal characteristics by checking both their medical and obstetric records. Patients were divided in groups based on using CNI-based or CNI-free immunosuppression during the first trimester of pregnancy. For statistical analyses we used one-sample T, Mann-Whitney-U and Chi-square tests.

*Results: We identified 129 pregnancies with CNI during pregnancy (CNI+) and 125 without CNI (CNI-). Demographic statistics did not differ except for higher BMI in CNI+ (25.3 vs 23.7, P=0.01) and the year of transplant (median 2000 for CNI+ vs 1989 for CNI-, P<0.01). In the 3^rd trimester creatinin levels were significantly higher in CNI+ (127 vs 105, P<0.01). The percentual increase in creatinin from preconceptional to the 3^rd trimester level was also higher in CNI+ (+3.1% vs -2.2%, P=0,05). In both groups, a postpartum 11-12% increase of creatinin from preconceptional level was observed (p=0,92). Regarding fetal outcomes, in CNI+ more children were born with birth weight <2500 gr (27% vs 19%, p=0,07). Other obstetric and fetal outcomes were comparable in both groups.

*Conclusions: Our data indicate that CNI do not negatively influence the course of renal function on a short term after pregnancy, but only temporarely cause a higher increase in serum creatinin levels towards the end of pregnancy. This suggests that it is not necessary to replace CNI by azathioprine to preserve renal function. However, the multidisciplinary team taking care of these high risk pregnancies needs to be aware of the lower birth weight observed in neonates born to women using a CNI. Our data do not allow to draw conclusions on possible long term negative effects of CNI on overall health outcome of mother and children. This will be subject of future studies.

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