Maternal stress may lead to a number of risk factors for stillbirth, and evidence from a large Swedish population-based study suggests that severe stress may be associated with increased stillbirth risk.[1] Analyses using data on three million births in 1973–2006 indicate that the risk of delivering a stillborn infant was elevated by nearly 20% among women who had experienced the loss of a close relative—one of "the most severe sources of stress a person can experience"—around the time of a pregnancy. The association was generally the same regardless of whether the death had occurred during or within the year before the pregnancy; it was unchanged in analyses including a variety of potential mediators.

The researchers used a national birth register to identify all births that occurred at gestations of 28 weeks or later during the study period. They linked data on these births to information from four other national registers to assess maternal background, family, psychosocial and health characteristics, including the death of a close relative (specifically, a parent, child or sibling) during or in the year prior to the pregnancy. To investigate the relationship between loss of a close relative around the time of pregnancy and stillbirth risk, they conducted a series of Cox regression analyses, controlling for a wide range of variables.

Three million births were recorded during the study period; 3% were among women who had lost a close relative during or within a year before the pregnancy. Bereaved mothers differed from others on a number of measures. For example, they were older and higher parity, they were more likely to have smoked early in pregnancy and they were somewhat more likely to bear an infant who was small for gestational age. However, the two groups were similar in the proportions who experienced multiple pregnancies, had prepregnancy diabetes or chronic hypertension, were obese, and had preeclampsia or antepartum hemorrhage.

In all, 11,071 infants (3.8 per 1,000) were stillborn. Women who had experienced the death of any close relative were significantly more likely than others to have a stillbirth (hazard ratio, 1.2). The risk was significantly elevated for those who had lost a child (1.7) and for those who had lost a sibling (2.1), but not for those who had lost a parent. Losses both before and during pregnancy were associated with increases in risk (1.2 for each).

Additional analyses revealed no mediating effects of an infant's having been small for gestational age or of a mother's having smoked early in pregnancy, had preeclampsia or had vaginal hemorrhage. The investigators also found no difference in the association between maternal bereavement and stillbirth risk if they stratified stillbirths by time of occurrence—before versus during delivery, or preterm (i.e., at 28–36 weeks’ gestation) versus at term.

The researchers note a number of limitations to their study. Among these are the exclusion of births that occurred at gestations of less than 28 weeks and the possibility that genetic characteristics or other, unmeasured variables may have a role to play. The investigators acknowledge that additional research is needed to confirm their results and to identify the physiological mechanisms underlying the association between maternal bereavement around the time of pregnancy and stillbirth risk. Because both of these are rare events, they conclude that "the practical implications of [the] findings are likely to be modest." They suggest that future work examine "whether stressors that are less severe but are common and thus eventually more important from a public health viewpoint are also associated with stillbirth."—D. Hollander

Reference

1. László KD et al., Maternal bereavement during pregnancy and the risk of stillbirth: a nationwide cohort study in Sweden, American Journal of Epidemiology, 2013, 177(3):219–227.