Risk of affective disorders following prenatal exposure to severe life events: a Danish population-based cohort study.

OBJECTIVE To examine the effect of prenatal exposure to severe life events on risk of affective disorders in the offspring. METHODS In a cohort of 1.1 million Danish births from May 1978 until December 1997, mothers were considered exposed if one (or more) of their close relatives died or was diagnosed with serious illness up to 6 months before conception or during pregnancy. Offspring were followed up from their 10th birthday until their death, migration, onset of affective disorder or 31 December 2007; hospital admissions were identified by linkage to the Central Psychiatric Register. Log-linear Poisson regression was used for data analysis. RESULTS The risk of affective disorders was increased in male offspring whose mothers were exposed to severe life events during the second trimester (adjusted RR 1.55 [95% CI 1.05-2.28]). There was an increased risk of male offspring affective disorders in relation to maternal exposure to death of a relative in the second trimester (adjusted RR 1.74 [95% CI 1.06-2.84]) or serious illness in a relative before pregnancy (adjusted RR 1.44 [95% CI 1.02-2.05]). There was no evidence for an association between prenatal exposure to severe life events and risk of female offspring affective disorders. CONCLUSIONS Our population-based study suggests that prenatal maternal exposure to severe life events may increase the risk of affective disorders in male offspring. These findings are consistent with studies of populations exposed to famine and earthquake disasters which indicate that prenatal environment may influence the neurodevelopment of the unborn child.