FAIRFAX, VIRGINIA — The lack of data on optimal timing of delivery for pregnancies complicated by diabetes remains a major challenge in obstetrics — one with considerable implications given the high and rising prevalence of pregestational and gestational diabetes, Katherine Laughon Grantz, MD, MS, of the National Institute of Child Health and Human Development, said at the biennial meeting of the Diabetes in Pregnancy Study Group of North America.
“While 39-40 weeks might be ideal for low-risk pregnancies, the optimal timing for pregnancies with complications [like diabetes] is unknown,” said Dr. Grantz, a senior investigator in the NICHD’s epidemiology branch.
The percentage of mothers with gestational diabetes mellitus (GDM) increased from 6% in 2016 to 8% in 2021, according to the most recent data from the National Vital Statistics System of the Centers for Disease Control and Prevention (MMWR Morb Mortal Wkly Rep. 2023;72:16). Meanwhile, the prevalence of prepregnancy obesity, which raises the risk of gestational and type 2 diabetes, was 29% in 2019; this represents an 11% increase from 2015 (NCHS Data Brief. 2020;392:1-8) and has occurred across all maternal ages, races, ethnic groups, and educational levels, she said.
“The reason clinicians deliver pregnancies with diabetes earlier is because there’s a decreased risk of macrosomia, shoulder dystocia, and stillbirth. And these risks need to be balanced with the increased risk of neonatal morbidity and mortality associated with earlier delivery,” said Dr. Grantz, who noted during her talk that delivery timing also appears to influence long-term neurodevelopmental outcomes. “Yet despite [diabetes in pregnancy] being so common, there is complete uncertainty about when to deliver.”
ACOG Recommendations, Randomized Trials (New And Old)
The American College of Obstetricians and Gynecologists, in a Committee Opinion on Medically Indicated Late-Preterm and Early-Term Deliveries, published in collaboration with the Society of Maternal-Fetal Medicine, offers recommendations based on the type of diabetes and the level of control. For instance, the suggested delivery timing for well-controlled GDM is full term (39 0/7 to 40 6/7 weeks of gestation), while the recommendation for poorly controlled diabetes is individualized late preterm/early term management (Obstet Gynecol. 2021;138:e35-9).
In defining and evaluating control, she noted, “the clinical focus is on glucose, but there are likely other important parameters that are not taken into account ... which [could be] important when considering the timing of delivery.” Potentially important factors include estimated fetal weight, fetal growth velocity, lipids, and amino acids, she said.
ACOG’s recommendations are based mainly on retrospective data, Dr. Grantz said. Only two randomized controlled trials have investigated the timing of delivery in the context of diabetes, and both focused on cesarean section and were “generally underpowered to study neonatal outcomes,” she said.
The first RCT, published in 1993, enrolled 200 women with uncomplicated insulin-requiring diabetes (187 with GDM and 13 with pregestational diabetes) at 38 weeks of gestation, and compared active induction of labor within 5 days to expectant management. There was no significant difference in the cesarean delivery rate (the primary outcome), but rates of macrosomia and large for gestational age were higher in the expectant management group (27% vs. 15%, P = .05, and 23% vs. 10%, P = .02, respectively). Shoulder dystocia occurred in three deliveries, each of which was expectantly managed (Am J Obstet Gynecol. 1993;169[3]:611-5). Notably, the study included “only women with excellent glucose control,” Dr. Grantz said.
The second RCT, published in 2017 by a group in Italy, enrolled 425 patients with GDM (diagnosed by the International Association of Diabetes and Pregnancy Study Groups criteria) between week 38 and week 39 of gestation and similarly randomized them to induction of labor or expectant management. No difference in cesarean delivery was found (BJOG. 2017;124[4]:669-77). Induction of labor was associated with a higher risk of hyperbilirubinemia, and there was a trend toward a decreased risk of macrosomia, but again, the study was underpowered to detect differences in most outcomes, she said. (The study also was stopped early because of an inability to recruit, she noted.)
Dr. Grantz is currently recruiting for a randomized trial aimed at determining the optimal time between 37 and 39 weeks to initiate delivery — the time when neonatal morbidity and perinatal mortality risk is the lowest – for uncontrolled GDM-complicated pregnancies. The trial is designed to recruit up to 3,450 pregnant women with uncontrolled GDM and randomize the timing of their delivery (NCT05515744).
Those who are eligible for the study but do not consent to participate in randomization for delivery will be asked about chart review only (an estimated additional 3,000). The SPAN TIME study will also assess newborn development and behavior outcomes, as well as anthropometric measures, as secondary outcomes. An exploratory analysis will look for clinical, nonclinical or biochemical factors that could be helpful in optimizing delivery timing.