Objective To evaluate the sex ratio among pregnancies complicated by first trimester hyperemesis gravidarum and extend previous findings to include a measure of severity.
Design Population-based case control study.
Setting All non-federal hospitals in Washington State.
Population Two thousand and one hundred and ten pregnant women hospitalised for hyperemesis gravidarum and 9783 pregnant women without hyperemesis gravidarum.
Methods The infant sex ratio for pregnant women admitted to the hospital for hyperemesis gravidarum was evaluated using the Washington State hospital discharge database linked to the birth certificate database for years 1987–1996. Cases were pregnant women hospitalised for hyperemesis gravidarum (International Classification for Diseases—9th edition [ICD-9] diagnosis code 643) in the first trimester. Controls were women who experienced a singleton live birth and were not hospitalised for hyperemesis in Washington State during the same time period. Regression analysis with general estimating equations was used to calculate an odds ratio (OR) and 95% confidence interval (CI) to assess the association of hyperemesis gravidarum with infant sex ratio.
Main outcome measure Infant sex ratio.
Results Pregnant women hospitalised for hyperemesis gravidarum in the first trimester had a 50% increased odds of having a female infant compared with controls (OR 1.5, 95% CI 1.4, 1.7). Women hospitalised for three or more days had the greatest odds of having a female infant compared with control women (OR 1.8, 95% CI 1.5, 2.0).
Conclusion Hyperemesis gravidarum is associated with an increase in female live births and may be a marker for high oestrogen levels in utero.