Copenhagen: Researchers have found that exposure to Tylenol during pregnancy may be associated with differences in the reproductive organs of baby girls, while stressing that the study does not establish that the painkiller caused the changes or show that it affects fertility later in life.
The study, led by Margit Bistrup Fischer of Rigshospitalet in Copenhagen, examined 302 three-month-old girls whose mothers’ Tylenol use had been monitored during pregnancy.
Of the infants studied, 92 had been exposed to the medicine before 17 weeks of pregnancy, 67 were first exposed after 17 weeks, and 143 had not been exposed.
Researchers assessed exposure using urine samples collected from the mothers at regular intervals. The women generally used relatively small amounts of the medicine, and none exceeded the recommended maximum daily dose of 4,000 milligrams. Most reported taking it to treat headaches or musculoskeletal pain.
The researchers found that girls exposed to Tylenol in the womb had, on average, smaller ovaries and uteruses and fewer ovarian follicles than those who had not been exposed. Ovarian follicles contain immature eggs and are important to reproductive development.
Among babies exposed before 17 weeks of pregnancy, researchers also observed lower levels of anti-Müllerian hormone, which is associated with ovarian reserve.
The study also examined a separate group of 1,210 girls who had been followed from infancy into adolescence. In this group, prenatal Tylenol exposure was associated with smaller uteruses during puberty and smaller ovaries during adolescence.
However, the researchers cautioned that the findings cannot determine whether the observed differences will affect fertility, reproductive function or the age at menopause. Long-term follow-up will be needed to establish whether the changes have any lasting implications.
The study’s lead researcher said women who used Tylenol during pregnancy should not be alarmed by the findings, noting that many exposed girls had reproductive organ measurements similar to those of girls whose mothers had not taken the medicine.
Current guidelines continue to consider Tylenol, also known as acetaminophen in the US and paracetamol in many other countries, an option for treating pain and fever during pregnancy. Researchers noted that untreated high fever and severe pain can also pose risks to mothers and fetuses.
In an accompanying commentary, reproductive medicine specialist Christian De Geyter of the University Hospital of Basel noted that the findings were consistent with some animal research.
Geyter called for longer-term monitoring of girls exposed to Tylenol before birth, potentially through menopause, and added that the findings could prompt further review of recommendations on the medicine’s use during pregnancy.
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