A new University of Otago multinational study of 13 high-income countries found almost 8% of pregnancies in New Zealand were exposed to an opioid, compared with only 4% in Canada and 0.4% in the United Kingdom.
Co-author and University of Otago preventive and social medicine researcher Dr Sarah Donald said the findings were unexpected and the risks of opioid use needed to be better considered.
"Of the participating countries, only the United States and Iceland had higher prescribed use."
Co-author and fellow Otago researcher Prof Lianne Parkin said opioids crossed the placenta to the foetus, and during early pregnancy they could increase the risk of certain congenital malformations.
"They can also increase the risk of adverse outcomes such as preterm birth and low birth weight, breathing problems or withdrawal symptoms in the baby after delivery, and longer-term neurodevelopmental conditions."
Dr Donald and Prof Parkin said these risks needed to be considered when deciding whether to use opioids to treat moderate or severe pain during pregnancy.
"Opioid use will be influenced by local factors such as the prevalence of pain-related conditions, the organisation of the health system and approaches towards pain relief, but this between-country variation suggests it is time to take a look at the New Zealand guidelines," Dr Donald said.
Overall, the most common opioids taken were codeine and tramadol, and use was more common in late pregnancy and among those with lower income and higher body mass index.
The study analysed prescription analgesic opioid use during more than 20 million pregnancies, excluding during childbirth, from the years 2000 to 2020, and found use of prescription medication during pregnancy had increased over the period.
Absolute Midwifery registered midwife Alice Logie, of Dunedin, was "quite surprised" by the revelation.
She said she had a high number of home births in her practice and did not personally see a lot of opioid use in her patients.
"Generally speaking, a lot of home-birthing clients tend to veer away from medicine or traditional medical practices.
"So me personally, I don’t see a higher incidence of opioid usage in pregnancy.
"I know that usually, codeine definitely wouldn’t be a first thing that we would go for in pregnancy.
"Usually there’s a big conversation about alternative methods prior to codeine usage."
She said opioid use was not something her fellow midwives around Otago had noticed either.
She agreed with the researchers, that the higher use of opioids may reflect the increasing age of pregnant individuals who had a higher prevalence of medical conditions requiring treatment.
"Of course, our bodies aren’t as robust as we get older, and pregnancy is rather hard on the body.
"And also, just talking about the medical system, unfortunately our resources are very poor for things like physio for women who experience pain in pregnancy, whether that be pelvic pain or other complications of pregnancy.
"It reflects down the long line of lack of resources."
Dr Donald said it was unclear what was driving the increased use of opioids in pregnancy and further research was required.
