Recently, there have been reports of women who have previously struggled with infertility who were able to conceive after starting treatment with a glucagon-like peptide-1 receptor agonist (GLP-1) medication, such as semaglutide or tirzepatide.1,2 However, little is known about whether the use of weight loss medications, such as phentermine or GLP-1 medications, is correlated with certain pregnancy and neonatal outcomes.
We assessed 775,478 pregnancies for women with no history of diabetes and who did not develop gestational diabetes between January 2017 and April 2024. We first determined how often pregnant women were given a prescription for a weight loss medication, either phentermine or a GLP-1, in each trimester. We found that few women were prescribed weight loss medications during pregnancy, and fewer than 10 women (0.001%) were prescribed phentermine or a GLP-1 medication in the third trimester, as shown in Figure 1.
To determine whether there might be a relationship between weight loss medication use immediately before or during pregnancy and various maternal and neonatal outcomes, we compared the rates of preterm delivery, high birth weight, neonatal intensive care unit (NICU) admission, and diagnoses of failure to thrive or congenital heart defect for babies born to mothers prescribed phentermine or a GLP-1 medication in the 90 days before pregnancy or during the first trimester to those with no documented weight loss medication exposure during pregnancy. We were unable to assess the rates of these conditions for prescriptions in the second and third trimesters due to the very limited number of prescriptions for these medications during that timeframe. Women are represented in multiple trimesters if they had multiple prescriptions ordered in separate trimesters.
We found that babies born to mothers with a phentermine prescription in the 90 days prior to pregnancy were more likely to have a high birth weight than babies born to mothers not prescribed weight loss medications, as shown in Figure 2. Babies born to mothers prescribed a GLP-1 medication in the 90 days prior to pregnancy were more likely to require a NICU stay than babies born to mothers not prescribed weight loss medications. While the rates of pre-term deliveries were increased for both the phentermine and the GLP-1 group, after controlling for other risk factors, such as maternal age and BMI, the rates of pre-term delivery were similar for mothers prescribed weight loss medications and those with no weight loss medications.
Exposure to phentermine or GLP-1 medications in the first trimester yielded similar results to exposure in the 90 days prior to pregnancy, as shown in Figure 3.
