(395) Four Critical Weeks: GDM Screening at 24 vs. 28 Weeks in Singleton and Twin Pregnancies

Regardless of plurality, the glucose challenge test (GCT) and oral glucose tolerance test (OGTT) are recommended at 24–28 weeks for the diagnosis of gestational diabetes mellitus (GDM). However, there is no consensus on the optimal timing within this four-week window to optimize GDM detection rates. We assessed gestational age-specific GDM rates in singleton and twin pregnancies.

Study Design:

This retrospective study included nulliparous women from Maccabi Healthcare Services (2012–2022). The primary outcome of our study was to compare the rate of GDM diagnosis by OGTT timing (24–28 weeks) between singleton and twin pregnancies.

Results:

Among 84,620 pregnancies (82,786 singletons; 1,834 twins), twins had higher maternal age (30.5±5.4 vs. 28.2±5.0 years, p< 0.0001) and BMI (24.7±5.3 vs. 23.8±4.8, p< 0.0003). GDM was diagnosed in 4.9% of singleton pregnancies and 9.6% of twin pregnancies (p < 0.001), with comparable rates of GDMA1 and GDMA2 in both groups. Figure 1 shows that twin pregnancies also exhibited higher GCT levels than singleton pregnancies (126 ± 30 vs. 112 ± 29.0 mg/dL, p < 0.0001). This difference remained significant across all weeks within the 24–28-week testing time frame. Figure 2 illustrates the rates of GDM at the lower and upper limits of the 24–28-week gestational testing period. In singleton pregnancies, the diagnosis rate of GDM was 20% higher at 28 weeks compared to 24 weeks (5.0% vs. 4.2%, p = 0.004), whereas GDMA2 was more prevalent at 24 weeks than at 28 weeks (16.9% vs. 12.6%, p = 0.05). In twins, neither the rate of GDM diagnosis (6.9% vs. 8.6%, p = 0.70) nor that of GDMA2 (14.3% vs. 11.8%, p = 0.99) differed significantly between the two specified gestational ages.

Conclusion:

Twins had higher GCT levels and double the GDM rate of singletons. Singletons exhibited gestational age variability (higher GDM at 28 weeks, GDMA2 at 24 weeks), while twins showed no such pattern. We propose: (1) GCT at 24 weeks for singleton pregnancies when the GDMA2 risk peaks; and (2) maintaining flexibility for twin pregnancies between 24–28 weeks.