Maternal Fever in Early Pregnancy not Associated with Fetal Death

Danish authors of a study in this week’s issue of THE LANCET provide reassurance to pregnant women—maternal fever in the early stages of pregnancy is probably not a risk factor for miscarriage or stillbirth.

Increased maternal body temperature can cause fetal death in some animals, which has lead to the suspicion that maternal fever early in pregnancy (when embryonic development is at a critical stage) could have a similar effect in the human population.

Anne-Marie Nybo Andersen and colleagues from the Danish Epidemiology Science Centre, Statens Serum Institut, Copenhagen, and the University of Copenhagen, interviewed around 24,000 women who were recruited in the first half of pregnancy to the Danish National Birth Cohort Study. The investigators obtained information on the number of fever incidents during the first 16 weeks of pregnancy. For each fever episode, the highest measured body temperature, duration, and gestational age were recorded.

Around 5% of pregnancies resulted in miscarriage or stillbirth, and just under 20% of pregnant women had one or more fever episodes in the first 16 weeks of pregnancy. However, there was no association between maternal fever early in pregnancy and adverse fetal outcome—a finding that was consistent irrespective of measured maximum temperature, duration and number of fever incidents, or the gestational time of the fever incident, and was observed for fetal death in all three trimesters of pregnancy.

In an accompanying Commentary (p 1526), Kenneth Lyons Jones from the University of California San Diego, USA, concludes: “Because of the substantial barriers associated with the study of spontaneous abortion or fetal death, it is hard to imagine a feasible prospective study design that would be superior to that by Andersen and colleagues in addressing the risk associated with maternal fever. However, it is difficult to categorically conclude from this study, as do the investigators, that pregnant women need not fear a fetal death following an episode of fever.”

Contact: Dr Anne-Marie Nybo Andersen, Department of Social Medicine, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen, Denmark; T) +45 35 327974; E) a.nybo@socmed.ku.dk

Dr Kenneth Lyons Jones, Division of Dysmorphology/Teratology, Department of Pediatrics, University of California, San Diego, School of Medicine, La Jolla, CA 92103, USA; E) klyons@ucsd.edu