Value of Fasting Plasma Glucose to Screen Gestational Diabetes Mellitus Before the 24th Gestational Week in Women with Different Pre-Pregnancy Body Mass Index
Gestational diabetes mellitus (GDM) is a significant pregnancy complication associated with increased risks of maternal and neonatal morbidity. The condition is typically diagnosed between the 24th and 28th gestational weeks using the 75-g oral glucose tolerance test (OGTT). However, this late diagnosis leaves only a short window for managing blood glucose levels, which is crucial for reducing adverse outcomes. Early prediction of GDM could enable timely interventions, but it is challenging because fasting plasma glucose (FPG) levels decrease as gestational age increases. This study aimed to evaluate the value of FPG in screening for GDM before the 24th gestational week in women with different pre-pregnancy body mass index (BMI) categories.
The study was a multi-region retrospective cohort study conducted in China, involving women who had a singleton live birth between June 20, 2013, and November 30, 2014. Participants resided in Beijing, Guangzhou, and Chengdu and received prenatal care in 21 selected hospitals. Data on pre-pregnancy BMI, FPG before the 24th gestational week, and one-step GDM screening with 75-g OGTT at 24th to 28th gestational weeks were extracted from medical records. Women were classified into four groups based on pre-pregnancy BMI: Group A (underweight, BMI < 18.5 kg/m²), Group B (normal, BMI 18.5–23.9 kg/m²), Group C (overweight, BMI 24.0–27.9 kg/m²), and Group D (obesity, BMI ≥ 28.0 kg/m²).
The prevalence of GDM in the study population was 20.0% (6806/34,087). FPG levels decreased gradually as gestational age increased in all pre-pregnancy BMI groups until the 19th gestational week. Women with higher pre-pregnancy BMI had higher FPG levels. The study found that FPG before the 24th gestational week and pre-pregnancy BMI could be used to predict GDM. Specifically, the incidence of GDM in women with FPG ≥ 5.10 mmol/L between the 19th and 24th gestational weeks and pre-pregnancy overweight or obesity was significantly higher than in women with FPG ≥ 5.10 mmol/L and pre-pregnancy BMI < 24.0 kg/m² (78.5% vs. 52.9%, P < 0.001).
The study also examined the variation of FPG levels across different gestational weeks and pre-pregnancy BMI groups. FPG levels were highest in the early weeks of pregnancy and decreased steadily until the 19th week, after which they stabilized. For example, FPG levels were 5.08 ± 0.43 mmol/L at 4–5+6 weeks, 4.92 ± 0.46 mmol/L at 6–7+6 weeks, and 4.49 ± 0.44 mmol/L at 22–23+6 weeks. The downward trend was consistent across all BMI groups, but women with higher pre-pregnancy BMI consistently had higher FPG levels.
The predictive value of FPG for GDM was further analyzed using logistic regression models. The results showed that higher FPG levels and higher pre-pregnancy BMI were independently associated with an increased risk of GDM. For every 0.50 mmol/L increase in FPG levels above 4.10 mmol/L at the first prenatal visit, the incidence of GDM diagnosis later in pregnancy increased. The odds ratio (OR) for GDM was 3.1 (95% CI: 2.90–3.30) for higher FPG and 1.1 (95% CI: 1.06–1.13) for higher pre-pregnancy BMI.
The study also evaluated the receiver operating characteristic (ROC) curve of using FPG in the 19th to 24th gestational weeks to screen for GDM. The area under the curve (AUC) was 0.803 for women with pre-pregnancy BMI ≥ 24.0 kg/m², 0.679 for women with pre-pregnancy BMI < 24.0 kg/m², and 0.718 for the total population. These findings suggest that FPG ≥ 5.10 mmol/L between the 19th and 24th gestational weeks is a good predictor for GDM, particularly in women with pre-pregnancy overweight or obesity.
The study’s findings have important implications for the early diagnosis and management of GDM. By identifying women at high risk of GDM earlier in pregnancy, healthcare providers can initiate interventions to control blood glucose levels and reduce the risk of adverse maternal and neonatal outcomes. The study recommends that women with pre-pregnancy overweight or obesity and FPG ≥ 5.10 mmol/L between the 19th and 24th gestational weeks should be treated as having GDM.
In conclusion, this study demonstrates that FPG levels decrease as gestational age increases in different pre-pregnancy BMI groups, with the downward trend becoming insignificant after the 19th gestational week. Pre-pregnancy overweight or obesity is associated with higher FPG levels before the 24th gestational week. FPG ≥ 5.10 mmol/L between the 19th and 24th gestational weeks is a strong predictor of GDM, particularly in women with pre-pregnancy overweight or obesity. These findings support the use of FPG as a screening tool for GDM before the 24th gestational week, especially in high-risk populations.
doi.org/10.1097/CM9.0000000000000158
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