Risk of stillbirth in low‐risk singleton term pregnancies following fertility treatment: a national cohort study

Objective To assess the risk of stillbirth in low‐risk IVF pregnancies. Design Register‐based national cohort study. Setting Denmark 2003‐2013. Population Cohort of 425,732 singleton pregnancies including 10,235 conceived following IVF/ICSI, 4,521 conceived following IUI, and 410,976 spontaneous conceived. Methods Information on pregnancy, obstetrical risk factors, stillbirth, and fertility treatment was obtained from the Danish national health registers for all pregnancies after gestational week 21+6. We estimated the overall and gestational age specific risk of stillbirth in low‐risk term pregnancies following IVF, ICSI, and IUI. Further, we estimated the association between stillbirth and IVF and ICSI respectively as well as fresh or frozen‐thawed embryo transfer. Main outcome measures Risk of stillbirth. Results The number of stillbirth in spontaneously conceived and IVF/ICSI low‐risk term pregnancies was 525 (0.1%) and 35 (0.3%), respectively. In multivariate analysis, the risk of stillbirth in pregnancies following IVF/ICSI was increased (odds ratio (95% CI): 2.1 (1.4; 3.1)). The risk of stillbirth was correspondingly increased in time to event analyses taking risk time for each fetus into account from gestational week 37 and onwards (Hazard Ratio (95% CI): 2.4 (1.6; 3.6). In subanalyses, the risk of stillbirth was increased for pregnancies following ICSI (OR 2.2 (1.2; 3.1)), but not IVF (OR 1.7 (0.9; 3.1)). Conclusion We found a systematically increased risk of stillbirth in low‐risk term pregnancies following IVF/ICSI. Whether the risk was related to the treatment or underlying subfertility is uncertain. The results may indicate a need for obstetrical surveillance for these pregnancies when reaching term.