Flu drugs in, pesticides out for pregnant mums?

If you’re a pregnant woman looking to keep your unborn child safe and healthy, we’ve got some good news and some bad news for you.

The good news is that European researchers have found no increased risks to newborn babies if their mothers have taken drugs to prevent or treat influenza during pregnancy. Published in The BMJ, their study was the largest to date assessing potential risks of taking antiviral drugs (known as neuraminidase inhibitors) during pregnancy.

With pregnant women at risk of severe illness as a result of seasonal influenza, regulatory agencies in Europe and the USA recommend neuraminidase inhibitors for those with confirmed or suspected influenza, or those exposed to close contacts with the illness — despite limited knowledge on their safety and effectiveness during pregnancy. So researchers in Scandinavia and France decided to assess risks of adverse birth outcomes in association with neuraminidase inhibitors during pregnancy.

The study involved almost 6000 women who were prescribed any of the two neuraminidase inhibitors (oseltamivir or zanamivir) during pregnancy — and almost 700,000 women who did not receive prescriptions during a pregnancy in the same period (2008 to 2010). After several health-related factors were taken into account, the team found no increased risks of adverse outcomes including low birth weight, low Apgar score, preterm birth, stillbirth or birth defects. The findings remained the same when the analyses were restricted to oseltamivir exposure only.

The researchers acknowledged that their study included some limitations — for example, the study did not assess risks of adverse outcomes before 22 weeks of pregnancy, and some women could have filled a prescription without taking the drug. However, they maintain that their results support previous findings that the use of neuraminidase inhibitors is not associated with increased risks of adverse foetal or neonatal outcomes.

The bad news, however, is that another group of European researchers has suggested that pregnant women exposed to chemicals called pyrethroids — used in pest control for people, pets and crops — may go on to experience behavioural difficulties in their six-year-olds.

Pyrethroids are synthetic chemicals which are found in a range of products, including treatments for head lice, scabies and fleas, as well as some mosquito repellents. While they are considered a safer alternative to organophosphates, they work by damaging nerves; concerns have thus been raised about the potential impact of children’s exposure to them.

With this in mind, French researchers measured levels of five pyrethroid metabolites in the urine of 287 women between six and 19 weeks of pregnancy, and subsequently their six-year-olds, to see if there was any link between prenatal and childhood exposures and behaviour that might be indicative of neurodevelopmental damage (perhaps as a result of altered neurochemical signalling in the brain). Their findings were published in the journal Occupational & Environmental Medicine.

Three metabolites (trans-DCCA, cis-DBCA and cis-DCCA) showed up the most frequently in the urine samples of both the mothers (100%, 68% and 65%, respectively) and their children (96.5%, 85% and just under 65%, respectively). Higher levels of cis-DCCA in the urine of the mothers-to-be was associated with a heightened risk of internalising behaviours in their six-year-olds; levels of another metabolite (3-PBA) in the children’s urine samples were associated with a heightened risk of externalising behaviours; and high levels of trans-DCCA were associated with a lowered risk of externalising behaviours. Ultimately, children with the highest levels of metabolites in their urine were around three times as likely to display abnormal behaviour.

The researchers noted that their study was only observational, so no firm conclusions could be drawn about cause and effect. Additionally, they said that accurately assessing pyrethroid exposures using urine samples is notoriously difficult because metabolites are cleared from the body in just a few days. It was therefore with caution that they made their conclusion that “exposure to certain pyrethroids at the low environmental doses encountered by the general public may be associated with behavioural disorders in children”.