Title: Maternal bereavement after death of a close relative and neural tube defect in the offspring Background: Neural tube defects are the second most common and often lethal congenital anomaly in the world leaving surviving children with life-long severe disabilities. A low intake of folic acid is the best-known cause of the disease. Objective: To investigate if severe emotional stress exposure related to maternal bereavement due to loss of a close relative in the antenatal period is associated with neural tube defect in the offspring. Methods: A nationwide register-based follow-up study including all children born in Denmark from 1978-2008 and their mothers (n=1,734,190). In the time window of one year before pregnancy or during the first trimester of pregnancy 34,407 mothers were exposed to bereavement. Results: A total of 5,031 cases of neural tube defects were identified: 889 with spina bifida and 2,095 with hydrocephalous. For all neural tube defects combined no significant association was seen (OR 1.07, 95% CI: 0.88; 1.31), however stratified on sex a higher risk was seen in girls compared to boys. Moreover, when bereavement was due to death of an older child an increased risk was seen (OR 1.61, 95% CI: 1.07; 2.41). Discussion: We only studied live born children but about 2/3 of children with spina bifida survive the birth or longer with corrective surgery. We did not adjust for folic acid, but a sub-analysis of approximately 85,000 mothers showed no difference in intake during pregnancy in exposed and unexposed mothers. Results would be biased if more exposed mothers accept prenatal ultrasound screening and select induced abortion. If so a measure of association would be biased for more recent years. Conclusion: Bereavement due to death of an older child may be a risk factor for neural tube defects. However, this study needs to be replicated in a sample including pregnancies terminated due to neural tube malformations.