If you’re a pregnant woman with diabetes—whether it’s preexisting or gestational—you’re either managing it with diet and exercise alone or with insulin. Oral medications to lower blood glucose, like metformin, are not prescribed in pregnancy since the drugs can cross the placenta and, it’s been thought, might adversely affect the fetus. But a new study out of New Zealand has found no significant ill effects from using metformin in gestational diabetes.

The study looked at about 750 women with gestational diabetes. Half received metformin, and the other half used insulin for blood glucose control. The researchers analyzed a number of measures, such as birth trauma and respiratory distress, to assess neonatal health and found, overall, similar outcomes for insulin and metformin.

A few differences did emerge, however. For example, there were more pre-term births in the metformin group. And there was a greater incidence of low blood glucose among the newborns within two hours of birth in the insulin group. Though it needs more study, lead author Janet Rowan, MB, ChB, an obstetric physician at Auckland City Hospital, believes the difference in neonatal hypoglycemia rates between the groups may present an advantage to treatment with metformin. Additionally, the current study found that women preferred metformin to insulin. Three quarters of women on metformin said they would use the drug again should they develop gestational diabetes in future pregnancies, while only one quarter of the women on insulin would repeat their treatment experience if given the choice.

Rowan and her colleagues intend to do follow-up studies of the children at 2 years of age. The authors advise caution in the use of metformin to treat gestational diabetes until after the follow-up is complete.

This study was published in the May 8, 2008, issue of the New England Journal of Medicine.