GRAPEVINE, TEX.* – Pregnant women with type 2 diabetes or prediabetes had significantly less gestational weight gain if they had metformin exposure at any point in their pregnancies, with no differences in infant birth weight or postnatal infant hypoglycemia, according to research presented at the meeting sponsored by the Society for Maternal-Fetal Medicine.
In a retrospective single-center review of 284 women without metformin exposure and 227 with metformin exposure in pregnancy, metformin exposure at any point in pregnancy was associated with a significantly greater chance of appropriate – rather than excessive – weight gain.
The relationship held true for the 169 women who had metformin in their first trimester of pregnancy. Here, 69% of women had appropriate weight gain using Institute of Medicine and American College of Obstetricians and Gynecologists standards, compared with 54% of the 282 women who had no metformin exposure (adjusted odds ratio 1.92, P = .003). A further 22% of women receiving metformin in their first trimester of pregnancy lost weight, compared with 9% of women without metformin exposure (aOR 2.11, P = .019). There was no significant difference between the two groups in infant birth weight.
Separately, study author Jacquelyn Adams, MD, and her colleagues analyzed outcomes for the full cohort of 227 women who received metformin at any point in their pregnancy, comparing them again to the 282 women who had not received metformin. Most women (85%) were on 2 g of metformin at the time of delivery. These results again showed a greater likelihood of appropriate weight gain in the metformin group (69%; aOR 1.85; P = .002). Maternal weight loss was seen in 20% of this group (aOR 1.98, P = .018). Infant birth weights were not significantly different between these two groups.
“We found that women who had been on metformin at any point in their pregnancy had more appropriate weight gain and less excessive weight gain,” said, a maternal-fetal medicine fellow at the University of Wisconsin–Madison. “Actually, some women on metformin had even had a little bit of weight loss, with no difference in their baby’s birth weight. So that’s really exciting, because our starting prepregnancy body mass index was 33-36 [kg/m2], which is considered obese,” she said in an interview.
This is an important finding, said Dr. Adams, because previous work has shown that less weight gain in pregnancy is associated with lower risk for hypertension and preeclampsia, and lower rates of fetal macrosomia.
What about infant outcomes? Dr. Adams said that there were many concerns about metformin: “Would it affect baby outcome? Were those babies more likely to be hypoglycemic? Were they more likely to be growth restricted? Were they more likely to have issues in the NICU? And the answer was really, ‘No.’ ”
“So we can both help these women have appropriate weight gain and not have any negative effects on these babies,” she added.
Specifically, Dr. Adams and her coinvestigators found no significant differences between the groups in gestational age at birth, likelihood of neonatal ICU admission, Apgar scores, neonatal hypoglycemia, respiratory distress syndrome, or fetal death. Fetal growth restriction and anomalies occurred at a low and similar rate between the groups.
Dr. Adams said that she was not surprised to see that metformin was associated with less weight gain in pregnancy, but she was surprised at how highly significant the differences were with metformin use. “Metformin is first-line for diabetes in nonpregnant individuals because it’s associated with things like weight loss, and because of ease of use and lack of hypoglycemia – so I was really hoping to see this kind of result.”
Women receiving metformin were a mean 34 years old, while those who didn’t get metformin were 32 years old, a significant difference. Prepregnancy body mass index also was higher in those receiving metformin, and they were more likely to have a type 2 diabetes diagnosis. A similar proportion of both groups – about two-thirds – were white, and about 20% were Hispanic.
The lower weight gain seen in metformin-takers also might smooth the way post partum, said Dr. Adams. “My perception is that, when these women leave us, they might not have any primary care follow-up; they might not have anybody following their diabetes; and metformin is a very viable way to help them in their life outside of pregnancy.
“Not to mention that all the weight you gain in pregnancy, you do eventually have to lose post partum,” she added, “so having less pregnancy weight gain kind of sets them up for success in their postpregnancy life as well.”
Asked whether these results inform the ongoing question of whether insulin or metformin is the most appropriate first-line treatment for gestational diabetes, Dr. Adams first noted that “there’s a lot of crossover,” pointing out that over 60% of the participants in her study eventually also required insulin.
“It’s a question I would love to address in a head-to-head trial,” she said, adding that questions about metformin’s effects on the placenta and the potential for later deleterious effects require more study.
In her practice, Dr. Adams said that patients generally are discharged with a metformin prescription, and then meet with a diabetes educator 1 week after delivery to assess blood glucose levels and adjust medical management. Following that, a warm hand-off to a primary care practice who can continue management and education is optimal, she said.
In terms of next steps, “We would really love to look at metformin in the postpartum period,” said Dr. Adams. Ideally, future work could look for outcomes that extend beyond the 6- to 8-week postpartum follow-up visit. For example, she said, there are indications that women with insulin insensitivity might benefit from metformin while breastfeeding; it’s also possible that metformin might reduce the risk of postpartum preeclampsia.
Dr. Adams reported that she had no conflicts of interest and no outside sources of funding.
SOURCE: Adams J et al. .
*This story was updated 2/10/2020.