Common diabetes drug cuts preterm birth risk among high-risk mothers

Metformin was linked to lower odds of preterm birth among pregnant women at high metabolic risk, but did not prevent gestational diabetes overall.

The study examined whether metformin, a low-cost prescription oral medicine used to manage blood sugar, could prevent gestational diabetes and other adverse pregnancy outcomes, including early birth.

Gestational diabetes, which is characterised by elevated blood sugar during pregnancy, affects one in five pregnant women in Australia and can trigger premature labour in severe cases.

While metformin’s long-term impacts during pregnancy continue to be studied, researchers found it did not prevent gestational diabetes overall, but could offer significant protective benefits against premature delivery.

Preterm birth means delivery before 37 weeks and remains a leading cause of mortality and morbidity for mothers and babies. More than 26,000 babies, around 8 per cent of all births, are born prematurely in Australia each year, putting infants at risk of respiratory distress, developmental complications and prolonged stays in neonatal intensive care.

Associate Professor Aya Mousa, head of Diabetes, Metabolic and Reproductive Health Research at the Monash Centre for Health Research & Implementation, said women taking metformin had 35 per cent lower odds of giving birth before 37 weeks than those receiving a placebo.

She said: “Metformin helps the body use insulin more effectively to lower blood sugar.

“We found women taking metformin had fewer births before 37 weeks.

“This included halving the rate of births before 34 weeks – down to 2.2 per cent, compared with 4.4 per cent in the placebo group.

“Among those who did deliver prematurely, pregnancy was prolonged by an average of 11 days for women on metformin.”

Researchers analysed individual patient data from seven randomised, placebo-controlled trials involving 2,297 pregnancies at high metabolic risk.

Participants included women with higher body weight, insulin resistance, or polyendocrine metabolic ovarian syndrome (PMOS, previously known as PCOS).

Mousa said metformin’s effect on preterm birth warranted further investigation.

She said: “While these findings need to be confirmed in trials specifically designed to investigate preterm birth, including exploring optimal timing for starting metformin, they point to an important potential benefit that warrants further research.”

The study is part of the Metformin in Pregnancy Study (MiPS), a large international collaboration led by Monash researchers bringing together individual participant data from randomised trials in thousands of women and examining metformin use during pregnancy.

Professor Helena Teede, director of the Monash Centre for Health Research & Implementation and an endocrinologist at Monash Health, said the international collaboration helped address an important evidence gap around metformin use in pregnancy, with further questions now being addressed using the data.

Isolated studies have previously produced mixed findings and have not been large enough to definitively determine metformin’s effects, including in preventing gestational diabetes.

Teede said: “By bringing together the original data from thousands of women across international trials, we could examine individual participants and account for differences such as age, body mass index, blood glucose levels and when treatment began, giving us a clearer picture of metformin’s effects during pregnancy.”

Metformin did not affect other pregnancy outcomes examined, including birth weight, high blood pressure, pre-eclampsia, induction of labour or Caesarean section.

The broader MiPS collaboration is also investigating the long-term outcomes of metformin exposure during pregnancy.