Screening for Gestational Diabetes

The US Preventive Services Task Force (USPSTF) has recently published recommendations on screening for gestational diabetes.

Gestational diabetes is diabetes that develops during pregnancy in someone who did not have diabetes prior to pregnancy. This can happen because the hormone changes of pregnancy cause pregnant persons to become more resistant to insulin, the hormone that keeps blood sugar levels under control. This results in a need for increased insulin production by the body during pregnancy, and some people cannot make enough extra insulin to meet this need.

Gestational diabetes typically develops in the second or third trimester. People who have a new diagnosis of diabetes in their first trimester of pregnancy are more likely to have previously undiagnosed type 2 diabetes than gestational diabetes. Gestational diabetes increases the risk of having preeclampsia, infants that are larger than average size (fetal macrosomia), and cesarean delivery. Treatment for gestational diabetes includes lifestyle changes (diet and exercise) and in some cases medications (such as insulin injections).

Screening for gestational diabetes is typically done with an oral glucose challenge test or oral glucose tolerance test. This involves drinking a liquid that has a set amount of glucose (sugar) (50 g or 75 g) and then having blood drawn and blood sugar level measured after a set number of hours to make sure that it is not too high. Screening is typically done in the second trimester, between 24 and 28 weeks of gestation.

This recommendation applies to pregnant persons who do not already have a diagnosis of type 1 or type 2 diabetes.

The goal of screening for gestational diabetes is to identify and treat it earlier rather than later during pregnancy, and in doing so, prevent adverse maternal and fetal outcomes. While no randomized clinical trials have directly looked at how screening for gestational diabetes affects maternal and fetal outcomes, there is evidence from trials that treatment for gestational diabetes decreases the chance of adverse outcomes such as cesarean delivery, fetal macrosomia, and birth injury or shoulder dystocia (a complicated type of delivery). There is also evidence that the oral glucose challenge/tolerance tests can accurately detect gestational diabetes after 24 weeks of gestation.

Potential harms of screening include psychological stress as well as increased medical monitoring and interventions (particularly during labor and delivery and the immediate postpartum period) that come with having a diagnosis of gestational diabetes. There is also a potential side effect of low blood sugar in both mother and infant as a result of treatment, but this is uncommon.

The USPSTF concludes with moderate certainty that there is a moderate net benefit to screening for gestational diabetes at 24 weeks of gestation or after to improve maternal and fetal outcomes. The USPSTF concludes that the evidence on screening for gestational diabetes before 24 weeks of gestation is insufficient, and the balance of benefits and harms of screening cannot be determined.

Conflict of Interest Disclosures: None reported.

Source: US Preventive Services Task Force. Screening for gestational diabetes: US Preventive Services Task Force recommendation statement. Published August 10, 2021. doi:10.1001/jama.2021.11922