Mothers who experience a severe form of morning sickness known as hyperemesis gravidarum are 53% more likely to have a child diagnosed with autism spectrum disorder (ASD), according to a study in the American Journal of Perinatology. Researchers reviewed electronic health records of 469,789 pregnant women and their children born in Southern California between 1991 and 2014. Hyperemesis gravidarum was associated with increased risk of autism when the condition was diagnosed during the first and second trimesters of pregnancy, but not when it was diagnosed only in the third trimester. In addition, the association between hyperemesis gravidarum and ASD was stronger in girls than in boys and among whites and Hispanics than among African Americans and Pacific Islanders. Use of medications to treat hyperemesis gravidarum did not affect the risk of ASD. HG diagnosis is associated with ASD risk and may be helpful in identifying at-risk children who could benefit from enhanced surveillance and earlier diagnosis and intervention.