Maternal age is an established risk factor for gestational diabetes mellitus (GDM), but there is no consensus on the age above which there is significantly increased risk of GDM. In the literature, the lowest cutoff is ≥25 years, as recommended by the American Diabetes Association (1), but there are little data to support this recommendation. To determine the age threshold for increased risk of GDM, we have reviewed the prevalence of GDM, diagnosed by the World Health Organization criteria (2), in the singleton pregnancies managed in our department from 1998 to 2001. Data on maternal anthropometric parameters, parity status, and risk factors for GDM such as booking weight ≥70 kg, BMI ≥25 kg/m2, chronic hypertension, significant medical history, and smoking, as well as risk factors identified in our population that included carrier of thalassemia trait (3) and HBsAg (4) and presence of iron deficiency anemia, which reduces the risk of GDM (5), were retrieved from a computerized database. The pregnancies were categorized according to maternal age, i.e., ≤20 years, 20–24 years, 25–29 years, 30–34 years, 35–39 years, and ≥40 years, for statistical analysis (SPSS for Windows version 11.0; SPSS, Chicago, IL) using the χ2 test and Pearson’s correlation. Multivariate analysis was used to determine the role of advancing maternal age adjusting for the other significant associated factors, and the adjusted relative risk and 95% CI was calculated for each age cohort with the 20–24 years cohort as the reference.
Of the 16,383 women managed in this period, 15,827 (96.6%) women continued their pregnancies beyond the first trimester, and the number (% of total) from the youngest to the oldest cohort were 318 (2.0%), 1,713 (10.8%), 4,446 (28.1%), 5,457 (34.5%), 3,279 (20.7%), and 614 (3.9%), respectively. There was a significant difference and positive correlation in the prevalence of GDM, increasing from 1.3, 2.5, 6.2, 10.3, 21.7, and 31.9%, respectively, from the youngest to the oldest cohort (P < 0.001). On multivariate analysis and adjusting for significant confounding factors that included weight ≥70 kg, BMI ≥25 kg/m2, HBsAg carrier, thalassemia trait carrier, significant medical history, multiparity, smoker, and absence of iron deficiency anemia, the risk for the older cohorts was significantly increased as follows: 25–29 years, 2.59 (1.84–3.67); 30–34 years, 4.38 (3.13–6.13); 35–39 years, 10.85 (7.72–15.25); and ≥40 years, 15.90 (10.62–23.80). There was no significant difference for the <20 years cohort.
Our finding indicates that the risk of GDM becomes significantly and progressively increased from 25 years onwards. This supports the American Diabetes Association recommendation on the use of age ≥25 years as the cutoff for screening and the observation that maternal age ≥25 years is the factor most predictive of GDM (6). In clinical practice, maternal age of ≥25 years should be adopted instead of ≥35 years or 40 years as a risk factor for the development of GDM.
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