Primary outcome didn’t differ, but study findings point toward metformin benefit
The double-blind, placebo-controlled trial was conducted at two sites in Ireland, with 510 individuals (535 gestational diabetes pregnancies) enrolled between June 2017 and September 2022. In addition to usual care, they were randomly assigned 1:1 to either placebo or metformin (maximum 2,500 mg) at the time of gestational diabetes diagnosis and continued until delivery.
The primary outcome, a composite of insulin initiation or a fasting glucose ≥ 5.1 mmol/L at gestation weeks 32 or 38, did not differ significantly between the two groups, with risk ratio 0.89 (P = 0.13).
Insulin initiation occurred in 38.4% of the metformin and 51.1% of the placebo groups (relative risk, 0.75, P = .004). The amount of insulin required at the last assessment prior to delivery did not differ between the two groups (P = .17).
Mean fasting glucose was significantly lower with metformin vs. placebo at gestational week 32 (4.9 vs. 5.0 mmol/L; P = .03) and at gestational week 38 (4.5 vs 4.7 mmol/L; P < .001).
On average, those in the metformin group gained less weight between randomization and delivery (0.8 kg vs. 2.0 kg; P = .003).
Gestational week at delivery didn’t differ between the groups, both 39.1 weeks, nor did preterm births prior to 37 weeks’ gestation (9.2% metformin vs. 6.5% placebo; P = .33) or any other pregnancy-related complications.
More participants in the metformin group said that they would choose the drug compared with placebo (76.2% vs. 67.1%, P = .04).
Mean birth weight was lower in the metformin group compared with placebo, 3,393 g vs. 3,506 g (P = .005), with fewer weighing > 4,000 g (7.6% vs. 14.8%; P = .02) or being large for gestational age, i.e., above the 90th percentile (6.5% vs. 14.9%; P = .003).
Proportions of offspring that were SGA (less than 10th percentile) were 5.7% in the metformin group vs. 2.7% with placebo (P = .13).
There were no other significant differences in neonatal variables.
Dr. Dunne told this news organization that her group has recently received funding for long-term follow-up of the SGA offspring. “As other papers have pointed out, if there’s any hint of SGA that’s really important to follow up. So we’re now beginning our longitudinal follow up of the mother and infants to see if the small number that were SGA will in fact turn out to have an increase in body mass index and weight in their childhood and adolescent years.”
The trial was funded by the Health Review Board (HRB) of Ireland, coordinated by the HRB-Clinical Research Facility Galway, and sponsored by the University of Galway, Ireland. Metformin and matched placebo were provided by Merck Healthcare KGaA, Darmstadt, Germany (operating as EMD Serono in the United States), and blood glucose monitoring strips were provided by Ascensia.
Dr. Dunne reported nonfinancial support from Merck and matched placebo and nonfinancial support from Ascensia during the conduct of the study. Dr. Benhalima receives research funds from Flemish Research Fund, study medication from Novo Nordisk, and devices and unrestricted grants from Medtronic and Dexcom.
A version of this article appeared on Medscape.com.