Antihistamines During Pregnancy May Increase Risk of Adverse Outcomes

mom morning sickness A UCLA study has revealed that woman who deal with a severe form of nausea during pregnancy and take antihistamines to sleep it through, might be at risk of adverse pregnancy outcomes like preterm births or low term babies.

This is the first study that has linked the use of antihistamines during pregnancy with pregnancy outcomes. Study lead, author Marlena Fejzo, an assistant professor of research in obstetrics and gynecology at UCLA, said that women who do take the medication should know the risk involved.

Having a baby before 37 weeks of pregnancy may lead to increased hospitalization, problems with feeding and breathing, higher instances of infections, and developmental issues.

Severe morning sickness that is experienced by some women during pregnancy, is known as hyperemesis gravidarum (HG).

According to the researcher, the symptoms associated with such nausea are so intense that women in the study group said they experienced detached retinas, blown eardrums, cracked ribs, and torn oesophagi and these severe symptoms can last for months or even the entire pregnancy.

Fejzo had undiagnosed HG during her first pregnancy and nearly died during her second, losing the baby at 15 weeks gestation. Being someone who experienced the condition herself, she says she was quite surprised to find the link between antihistamine use and severe pregnancy outcomes.

“It was surprising to find the link between antihistamines and adverse outcomes as these are over-the-counter medications that are used commonly by women with HG during pregnancy. Women and their healthcare providers should be aware of the risk for adverse outcomes when deciding which medications to take to treat their HG symptoms.”

For the research, the team compared pregnancy outcomes in 254 women with HG who were sick enough that they needed treatment for dehydration with intravenous fluids to 308 women who had normal or no morning sickness during pregnancy. This was conducted for six years.

They found women with HG had four times more risk of adverse pregnancy outcomes. Fejzo also compared women with HG who had adverse outcomes with those who had good outcomes. They looked at about 35 medications that these women took to understand if there was a link between their pregnancy outcomes and the drugs they were taking.

She found that antihistamines, like those found in Unisom and Benadryl, were taken by more than 50 percent of HG patients who experienced adverse outcomes. She also noted that these medicines were effective in less than 20 percent of women.

“Some doctors will suggest that their HG patients take Unisom to help them sleep through their nausea,” Fejzo said. “Our findings show not only that the use of antihistamines is linked with adverse outcomes, but also that they’re not that effective. Women with HG should be aware of that so they can make educated decisions on how to treat their HG symptoms.”

The researcher says HG is diagnosed in 0.2 to 2 percent of pregnant women, although rates are higher in China. The team is now trying to find out if the severe vomiting and other symptoms experienced by mothers have any effect on their children later in life.

“We desperately need support for research into HG to determine its cause so that medications can be designed that are safe and effective,” Fejzo said. “The greatest risk factor for HG other than a previous HG pregnancy is having a sister who had HG, which increases the risk by 17-fold. This suggests a genetic component is at work.”

The researcher is also trying to study the DNA extracted from the saliva of women suffering from HG and women with normal pregnancies to see if any genes are responsible for severe nausea.

The study was funded by the Hyperemesis Education and Research Foundation and was published in the European Journal of Obstetrics and Gynecology and Reproductive Biology.


About the author


Atula is a writer, traveler, and a nature-lover. She is also mom to a boy who seems to have inherited all her creative genes. When Atula is not busy making up stories with her son, she writes for numerous magazines, websites, and blogs. She is also working on her site on endangered species called

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