Temporal changes in fetal death risk in pregnancies with preeclampsia: Does offspring birthweight matter? A population study

OBJECTIVES: To study the associations of preeclampsia with fetal death risk within percentiles of offspring birthweight, and whether these associations have changed during 1967–2014. STUDY DESIGN: In this population study, we included all singleton pregnancies in the Medical Birth Registry of Norway during 1967–2014 (n = 2 607 199). Odds ratios (ORs) for fetal death associated with preeclampsia were estimated within percentiles of birthweight by applying logistic regression analyses. We estimated ORs for the study period as a whole, and for the years 1967–1983 and 1984–2014. RESULTS: During the study period as a whole, preeclampsia increased the risk of fetal death, OR 2.73 (95% CI 2.57–2.89), and the fetal death risk associated with preeclampsia differed across percentiles of offspring birthweight. The overall risk of fetal death decreased during our study period, and the decrease was most prominent in preeclamptic pregnancies with low offspring birthweight (<1 percentile). Thus, in recent years, the risk of fetal death in pregnancies with low offspring birthweight was lower in preeclamptic than in non-preeclamptic pregnancies, OR 0.22 (95% CI 0.12-0.41). Only in pregnancies with offspring birthweight within the 10–90 percentiles, the risk of fetal death associated with preeclampsia remained significantly increased throughout the study period. CONCLUSIONS: The decline in fetal death risk was most prominent in preeclamptic pregnancies with low offspring birthweight. The introduction of a national screening program for preeclampsia in the 1980s, and identification of growth restricted offspring by fetal ultrasonography, may explain our findings.