Though it may be the bane of many a pregnant woman’s mornings, a new study shows that morning sickness — nausea and vomiting — is actually linked to lower incidence of miscarriage. The researchers aren’t sure exactly why, but speculate that it has to do with the individual hormone changes a pregnant woman experiences.
Women over 35 whose symptoms lasted the longest into their pregnancies had even less likelihood of miscarrying (up to 80% less than women who had no symptoms).
The authors of the study, which was led by Ronna L. Chan at UNC Chapel Hill, recruited women very early in their pregnancies or even while they were trying to become pregnant, so that they could follow them for as much time as possible. They found that 89% of the women experienced morning sickness — either nausea alone or nausea and vomiting. About 11% of the women in the study miscarried in the first half of their pregnancies.
The risk of miscarrying was over three times higher for women who experienced no symptoms of morning sickness than for women who did have morning sickness. This finding was particularly sensitive to age: for women under 25 years old, those who had no symptoms had four times the odds of miscarrying than women with symptoms of morning sickness.
Of course, women who had no symptoms of morning sickness also went on to carry to term, so pregnant women shouldn’t be alarmed at the study’s findings. The researchers are not sure exactly why the connection exists, but some experts have suggested that it could be a mechanism to ensure that the mother eats a healthy diet, or it could be a "reflection of maternal sensitivity to hormones…that themselves are related to pregnancy outcome". Still, it’s worth mentioning that the study did not show a cause-and-effect relationship between morning sickness and miscarriage, so the nature of the relationship is still unclear.
The study was published in the September 22, 2010 online issue of Human Reproduction.