If you are pregnant, or hoping to become pregnant, you may be thinking about the kinds of foods you should eat to keep yourself and your baby healthy — and the foods and behaviors you should avoid. As we learn more and more about what we can and can’t do during pregnancy, there are some behaviors we don’t even think about that can affect not only fertility but a baby's development.

Taking the painkiller acetaminophen, also known as paracetamol, the active ingredient in Tylenol and Panadol, during pregnancy may affect the child’s development and reproductive health — especially those of daughters, two recent studies have found.

Girls with language delays were six times more likely to have mothers who used acetaminophen more heavily than others.

The first study, from researchers at Mount Sinai’s Icahn School of Medicine and Karlstad University in Sweden, tracked 750 women during and after pregnancy. When the women were just a few months along in their pregnancies, they filled out questionnaires about their acetaminophen use up to that point. Then, when their children were 30 months old, mothers were asked about their children’s language abilities and a nurse evaluated the kids' language development.

In general, boys develop language later than girls. But when acetaminophen use was taken into account, things changed. About 60 percent of the women in the study used acetaminophen during their early pregnancies. And girls with language delays were six times more likely to have mothers who used acetaminophen more heavily than others.

Boys naturally start talking a little later than girls, so the current results, published in European Psychiatry, suggest that the “advantage” girls have in language acquisition is lost if their mothers take acetaminophen during pregnancy. Because of this study and other research suggesting risks of acetaminophen, the authors recommend women limit their use of the drug during pregnancy.

Many women take acetaminophen during pregnancy, exposing children prenatally, and because delayed language development is often a sign of other neurodevelopmental problems in children, pregnant women should try to limit their use of painkillers containing the compound, one of the study's authors, Shanna Swan, suggests.

The researchers plan to follow the participants over the years to see how the children’s language continues to develop later into childhood.

Prenatal Exposure and Impaired Fertility

The effects of taking acetaminophen during pregnancy may even extend to the next generation. In another study, published in Endocrine Connections, a team at Copenhagen University Hospital, examined the fertility of the offspring of rodents given acetaminophen during pregnancy. The study, a review of three previous studies, found that when rats and mice were given acetaminophen, their female offspring had fertility issues, including fewer eggs in their ovaries. This is important since both female rodents and female humans are born with a set number of eggs — they cannot make more throughout life.

Even the things that people do before they’re pregnant can have an effect on future generations.

“Although this may not be a severe impairment to fertility,” said study author, David Kristensen, in a statement, “it is still of real concern since data from three different labs all independently found that [acetaminophen] may disrupt female reproductive development in this way, which indicates further investigation is needed to establish how this affects human fertility.”

Earlier studies had pointed to reductions in male fertility linked to acetaminophen, so it’s interesting that this new one focused on female fertility. Again, it is not clear that a reduction in the number of eggs would necessarily seriously affect a woman’s fertility, but since the number of eggs is finite, and their quality decreases as women age, it may be relevant.

More work will need to be done to understand exactly why these connections exist, and what acetaminophen is doing to the female body and to the fetus. In the meantime, it’s best to limit use of any medication during pregnancy, and always talk to your doctor before taking a drug if you’re pregnant or expecting to be. Even the things that people do before they’re pregnant can have an effect on future generations.