New Clues To Morning Sickness Unveiled

February 15, 1997

Seattle, Wash. -- The same hormone that makes home pregnancy kits change color is significantly associated with and may be the cause of the nausea and vomiting of morning sickness, according to Penn State researchers.

"Higher human chorionic gonadotropin (hCG) levels are associated with an increased risk of experiencing pregnancy-related sickness during the first trimester of pregnancy," says Dr. Kathleen A. O'Connor, a National Institute of Aging Post-Doctoral Trainee at Penn State's Population Research Institute and research associate in anthropology.

"Estrogen and progesterone do not appear to contribute significantly to pregnancy-related sickness," she told attendees today (Feb. 15) at the annual meeting of the American Association for the Advancement of Science in Seattle.

hCG reaches a peak, drops and levels off during the first trimester of pregnancy. This hormone is produced during pregnancy and serves to maintain necessary levels of progesterone for pregnancy until the placenta is developed enough to take over this duty.

Previous experiments have suggested hCG or, less strongly, estrogen and progesterone as the cause of at least first trimester pregnancy-related sickness, but many studies only looked at hormone levels once or twice during the pregnancy and don't control for the actual date during pregnancy when the sample was taken. The Penn State researchers are looking at data collected in Bangladesh from about 200 women who supplied twice weekly urine samples and answered questionnaires for from one to nine months.

"These preliminary findings are from 15 women who supplied samples for up to nine months," says O'Connor.

The researchers, who include O'Connor; Darryl Holman, post-doctoral fellow at the Population Research Institute; James Wood, professor of anthropology; and Ellie Brindle and Sue Barsom, anthropology graduate students, have looked at 779 samples so far. Not all women experience pregnancy-related sickness, and not all pregnancy-related sickness is confined to the first trimester.

In the United States, the idea that morning sickness is a good thing, because it means the pregnancy is going well is widespread. However, not experiencing morning sickness does not foretell a miscarriage. Some women can have three perfectly normal pregnancies, yet experience nausea and vomiting during only one.

"What we have found in the Bangladesh data, however, is a link between pregnancy-related sickness and age," says O'Connor. "As women get older they tend to experience less pregnancy-related sickness. What also holds true is that many women over age 35 have a higher risk of fetal loss."

While many have made the connection between the absence of morning sickness and increased risk of fetal loss, O'Connor notes that those studies did not control for the age of the women. The real connection is between the increased age of women and fetal loss and the increased age of women and a decrease in pregnancy-related sickness , not between pregnancy-related sickness and fetal loss.

Ultimately the researchers will look at how hormones, especially hCG, change with maternal age.

"One question we can't answer yet is why some women experience pregnancy-related sickness on and off throughout pregnancy, rather than just during the first trimester," says O'Connor. "In our data and other studies, 5 to 25 percent of women experience nausea and vomiting later in their pregnancies."

***aem***

EDITORS: Dr. O'Connor may be reached at (814) 863-1474 or oconnor@pop.psu.edu on the Internet.

Penn State

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