Study question: Is maternal bereavement (emotional stress) due to loss of a close relative in the antenatal period associated with the risk of oral cleft in the offspring?
Summary answer: Our study suggests prenatal maternal bereavement is associated with an increased risk of oral cleft in the offspring, especially when the bereavement was due to a sudden death or death of a child.
What is known already: The aetiology of oral cleft is unknown but includes both genetic and environmental causes.
Study design, size and duration: We performed a population-based cohort study based on several national registers in Denmark from 1978 to 2008.
Participants/materials, setting, methods: Our final study population consisted of 1 771 663 children. Of these 35 118 (2%) were born to mothers who experienced bereavement in the exposure window from 1 year before pregnancy to the end of the first trimester.
Main results and the role of chance: In total, 3043 children were diagnosed with a cleft; 968 with cleft lip, 1206 with cleft lip and palate and 869 with a cleft palate. For overall bereavement the prevalence was 1.7 per 1 000 live born in the unexposed children and 2.2 per 1 000 live born in the exposed children. Overall, maternal bereavement due to the death of a close relative from 1 year before conception to the end of the first trimester was associated with a significantly increased risk of oral cleft [odds ratio (OR): 1.28, 95% confidence interval (CI): 1.01; 1.61). When mothers lost a relative due to a sudden death, the risk of oral cleft in the offspring was higher (OR: 1.76, 95% CI: 1.06; 2.94). Losing a relative in the time period before pregnancy and during the first trimester showed a tendency to an increased risk. The risk increase was 77% when the mother was bereaved due to sudden death and the estimation was robust in different analytical strategies.
Limitations, reasons for caution: It is a limitation that we only studied live born children, but most children with isolated oral cleft would survive their pregnancy and birth. Since oral cleft are rare and despite the large study population, we still had a relatively small number of cases, which results in limited power to detect small differences. We did not have actual measurements of the maternal cortisol concentration, but we believe that bereavement due to death of a close relative produces a strong stress reaction in most people. Also we did not have the opportunity to adjust for intake of folic acid and use of anti-depressant; however, analysis in a subset of the data showed no difference in these intakes between exposed and unexposed mothers.
Wider implications of the findings: With this study we add a large-scale human cohort study to the body of literature on stress and birth defects. Our study is in agreement with previously published results and can be generalized to similar populations like the native Danish population. Severe stress may be added to the list of potential causes for oral cleft.