Taking painkillers during pregnancy may impact fetus health, finds a new study published in Scientific Reports.

"In recent years, considerable attention has focused on the possibility that fetal exposure to 'endocrine disruptors' — weakly endocrine-active environmental chemicals — might cause adverse effects in the fetus," the study authors wrote. "In contrast, potential fetal effects resulting from exposure to pharmaceutical compounds have received comparatively little attention, although a recent study showed effects of several analgesics on hormone production by the human fetal testis. Of significant interest is the analgesic/anti-pyretic acetaminophen (paracetamol), which is used by the majority of women during pregnancy."

The authors cited prior research that associated pregnancy exposure to Tylenol with an increased risk of neurodevelopmental and ADHD-type disorders in children, while four independent studies have shown an increase risk of cryptorchidism in boys born to mothers either taking acetaminophen by itself or in combination with NSAIDs (Aspirin and Ibuprofren).

To test these potential effects themselves, study authors treated pregnant rats with either indomethacin (a prescription painkiller in the UK) or with paracetamol. Rats were given indomethacin for four days, while rats were given paracetamol for nine days. Not only did the painkillers affect a mother's offspring, but it affected the subsequent generation of rats.

There were "modest but detrimental" effects on fertility later in life for resulting female offspring, but not resulting male offspring. Females had reduced ovary size and altered reproductive function, which authors suggest also affect the development of germ cells — "cells that give rise to eggs and sperm" — while the fetus is still in utero.

As is the case with all animal research, it's hard to tell how these results translate to humans. Rats and humans have similar reproductive systems, but there are still limitations.

"A limitation of the human health relevance of the present studies is that we administered only a single dose of analgesics, which may not match human exposure regimens," the authors wrote. "Although the indomethacin dose used (0.8 mg/kg/day) is within the human therapeutic range, the dose of acetaminophen which we used, resulted in blood levels of acetaminophen 2.5- to 8-fold higher than the levels reported in humans after normal therapeutic dosing (~60 mg/kg/day, divided into 4 doses) during pregnancy."

However, study co-author Richard Sharpe, a professor of clinical reproductive science at the University of Edinburgh, said in a press release that these findings "follow previous research that indicates painkillers should be used with caution during pregnancy."

Next, Sharpe and his team plan to explore whether a short dose has similar effects, and how those study sets could be made useful for humans.

Source: Sharpe R et al. Analgesic exposure in pregnant rats affects fetal germ cell development with inter-generational reproductive consequences. Scientific Reports. 2016.