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Summary

The generalizability of the apparent decreased risk of miscarriage and perinatal mortality associated with early pregnancy nausea and vomiting was investigated by examining data available from 11 previous studies. Statistical reanalyses of these studies indicated a strong significant association of nausea and vomiting of pregnancy with decreased risk of miscarriage, and no consistent associations with perinatal mortality. A statistical meta-analysis confirmed the decreased risk of miscarriage associated with gestational nausea and vomiting (common odds ratio = 0·36, 95% CI 0·32 to 0·42) and indicated that the association with decreased fetal mortality was restricted to the first 20 weeks gestation. The meta-analysis also revealed that over 150 additional possibly unreported studies with contradictory evidence would be required to refute this observed association.