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Association between severe nausea and vomiting in early pregnancy and the risk of neural tube defects in Northern China.

BACKGROUND
This study assessed the association between severe NVP and the risk of NTD in offspring compared with a population and a malformed control group. We also assessed whether folic acid supplements modified this association.


STUDY DESIGN AND SETTING
A case-control study was conducted with subjects enrolled from June 19, 2002, to November 18, 2014, from a population-based birth defects surveillance system that monitors major external structural birth defects through active case ascertainment in Shanxi Province, China. The main comparison was between women with NTD-affected offspring who experienced NVP in early pregnancy versus those who did not. A multivariable logistic regression model was used to examine the associations between severe NVP and the risk of NTD while adjusting for potential confounding factors. The risk was estimated by calculating the odds ratio (OR) and 95% confidence intervals (CIs).


RESULTS
The adjusted OR (AOR) of severe NVP for NTDs was 3.25 (95%CI 2.56, 4.12) compared with the population control, and 1.65 (95%CI 1.00, 2.72) compared with the malformed controls. When stratified by intake of folic acid supplements, the AOR for severe NVP was 3.40 (95%CI 2.61, 4.42) in the non-intake of folic acid supplements stratum and 2.51 (95%CI 1.42, 4.43) in the intake of folic acid supplements stratum.


CONCLUSION
We conclude that severe NVP is associated with NTDs, and that severe NVP may be a consequence, rather than a cause, of NTDs.