Overall, potential benefits probably don’t outweigh potential harms.

Universal screening for gestational diabetes (GD) is recommended between 24 and 28 weeks of pregnancy (JAMA 2021; 326: 531-538). The American College of Obstetrics and Gynecology recommends considering earlier screening for women with body mass index 25 kg/m² or higher and at least one additional risk factor for GD (Obstet Gynecol 2018; 131: e49-e64). However, whether earlier screening and treatment improves outcomes is unclear.

To examine this issue, researchers performed oral glucose tolerance tests (2-hour 75-g OGTT) in 3681 pregnant women before 20 weeks’ gestation. The 802 women who met diagnostic criteria for GD were randomised to immediate treatment or to deferred (or no) treatment, pending results of repeat screening at 24 to 28 weeks. For two of the primary outcomes – pregnancy-related hypertension and neonatal lean body mass – outcomes were similar in the immediate-treatment and deferred-treatment groups. The third primary outcome, adverse neonatal outcomes (a composite of preterm birth, macrosomia, birth trauma, perinatal death, phototherapy and neonatal respiratory distress) occurred significantly less often in the immediate-treatment group (25% vs 30%). This difference was driven mainly by a lower incidence of neonatal respiratory distress; rates of serious respiratory distress did not differ between groups.

A study published in 2020 is the only other large, randomised trial of early screening for GD. A total of 900 pregnant women with obesity underwent either screening before 20 weeks’ gestation or routine screening at 24 to 28 weeks. Early screening did not lower the incidence of a composite outcome of adverse perinatal events; moreover, a secondary analysis suggested potential net harms for women who underwent early screening and had more risk factors.

Comment: Early screening for GD is becoming more common, given the rising prevalence of maternal overweight and obesity. An editorialist concludes that these two trials, taken together, call into question current recommendations for early screening and treatment among high-risk women. Routine screening at 24 to 28 weeks of pregnancy still appears to offer the best balance of benefits and harms – including for women at high risk for GD.

Marie Claire O’Dwyer, MB BCh BAO, MPH,
Clinical Assistant Professor in Family Medicine,
University of Michigan Medical School,  Ann Arbor, USA.

Simmons D, et al. Treatment of gestational diabetes mellitus diagnosed early in pregnancy. N Engl J Med 2023 May 5; e-pub (https://doi.org/10.1056/ NEJMoa2214956).
Harper LM, et al. Early gestational diabetes screening in obese women: a randomized controlled trial. Am J Obstet Gynecol 2020; 222: 495.e1-495.e8 (https://doi.org/10.1016/j.ajog.2019. 12.021).
Champion ML, et al. Early gestational diabetes screening based on ACOG guidelines. Am J Perinatol 2022 Dec 29; e-pub (https://doi.org/10.1055/ a-1925-1134).
Greene MF. Early versus second-trimester screening and treatment for diabetes in pregnancy. N Engl J Med 2023 May 5; e-pub (https://doi.org/10.1056/ NEJMe2304543).

This summary is taken from the following Journal Watch titles: General Medicine, Ambulatory Medicine, Women’s Health.