Researchers found that just two to seven days of exposure to the over-the-counter medication during the first trimester impacted follicle development in a fetus.

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Taking ibuprofen during your first trimester may harm the future fertility of your baby, if you're having a girl.

According to a report in Human Reproduction, consuming the pain reliever during the first three months of pregnancy may reduce the number of eggs stored in your daughter's ovaries.

Researchers found that just two to seven days of exposure to the over-the-counter medication caused germ cells in developing human ovarian tissue to die or not multiply at the usual rate. Germ cells are vital for follicle development.

"We indeed observed that ibuprofen induced tissue damage, however, we do not yet know how," says Séverine Mazaud-Guittot, Ph.D., who is the lead author of the study and a researcher at INSERM in Rennes, France. "Baby girls are born with a finite number of follicles in their ovaries…A poorly stocked initial reserve will result in a shortened reproductive life span, early menopause or infertility—all events that occur decades later in life."

The researchers looked at samples from 185 fetuses that were between seven and 12 weeks of development. The fetuses were from legally-induced terminations performed under the mothers' consent.

The amount of ibuprofen in umbilical cord blood was similar to the concentration in the blood of mothers who took 800 mg of the medication two to four hours prior to surgery.

"The fetus is exposed to the same concentration as the mother," Mazaud-Guittot said. "This is the first study to look at the effects of ibuprofen on the ovarian tissue of baby girls, and the first to show that ibuprofen can cross the placental barrier during the first trimester of pregnancy, exposing the fetus to the drug."

Dr. Mazaud-Guittot says the evidence raises concerns about the long-term impacts of taking ibuprofen with regard to the future fertility of women. The report states that about 30 percent of women are estimated to use ibuprofen during their first trimester.

Serena Chen, M.D., a fertility specialist from New Jersey who was not involved in the research, says women should avoid taking ibuprofen throughout pregnancy. "Ibuprofen should be avoided, if possible, during pregnancy in all trimesters as there is evidence that it can be harmful to the fetus if taken by the mother," she notes.

If you've taken ibuprofen during your pregnancy, don't panic. It's important to know that this is a small study and the scientists are still researching the subject. "The wisest advice would be to follow currently accepted recommendations: Paracetamol [also known as acetaminophen] should be preferred to any anti-inflammatory drug up to 24 gestational weeks, and the latter should not be used thereafter," Dr. Mazaud-Guittot says. "However, practitioners, midwifes, and obstetricians are best placed to give expert advice: every mother and every pregnancy is unique."