New Zealand has one of the highest rates of prescribed opioid use during pregnancy among high-income countries, according to a new international study.

The research, published in the journal Anesthesiology and led by the University of New South Wales, analysed more than 20 million pregnancies across 13 countries between 2000 and 2020. It found that nearly 8% of New Zealand pregnancies were exposed to opioids — behind only to the United States and Iceland.

Co-author Dr Sarah Donald, of the University of Otago’s Department of Preventive and Social Medicine, said the high rate in New Zealand was unexpected and raises questions about current medical guidelines.

“Of the participating countries, only the US and Iceland had higher prescribed use,” she said. “Opioid use will be influenced by local factors … but this between-country variation suggests it is time to take a look at the New Zealand guidelines.”

Codeine and tramadol were the most commonly prescribed opioids, with use more frequent in late pregnancy and among women with lower income or higher body mass index.

The study also noted that prescription medication use during pregnancy had generally increased over the past two decades.

“This general trend may reflect the increasing age of pregnant individuals … and growing recognition of the historic undertreatment of pregnant people,” Donald said.

“It is reassuring, though, that of those using an opioid during pregnancy, about 80% received just one prescription.”

Her Otago colleague and co-author, Professor Lianne Parkin, warned that opioid use during pregnancy carries risks.

“Opioids cross the placenta, exposing the foetus,” Parkin said. “They can increase the risk of congenital malformations, pre-term birth, low birth weight, and withdrawal symptoms in the baby after delivery.

“These risks need to be considered when deciding whether to use opioids to treat moderate or severe pain during pregnancy.”