Women With GDM, Vitamin D Deficiency May Have Higher Risk of Postpartum Glucose Intolerance

Vitamin D deficiency in women with gestational diabetes mellitus (GDM) is associated with an elevated risk of postpartum glucose intolerance, according to a study published in Endocrinology and Metabolism.

Researchers measured serum 25(OH)D levels mid-pregnancy in 348 Korean women with GDM diagnosed between August 2012 and October 2018. In addition, a 75-g oral glucose tolerance test was administered 6 to 12 weeks after delivery. Researchers classified Vitamin D deficiency as serum 25(OH)D <20 ng/mL.

The average age of women in the study was 33, while the average gestation period was 27.8 weeks. Of the 348 women included in the study, 267 (76.7%) were vitamin D deficient at baseline.

It has been documented that vitamin D deficiency is associated with type 2 diabetes (T2D) and metabolic syndrome; however, the causality of the association is unknown. GDM is defined as newly diagnosed unspecified diabetes (type 1 [T1D] or T2D) in the second or third trimester of pregnancy. The authors also note that vitamin D deficiency is common in pregnant women.

“Recently gathered evidence suggests that vitamin D deficiency in the first 2 trimesters of pregnancy increases the risk of insulin resistance and developing GDM,” the researchers said.

Women who were known to have had T1D or T2D prior to pregnancy were excluded from the study, as were individuals with thyroid disorders, twin pregnancy, and a history of taking vitamin D supplements during pregnancy.

The researchers found that vitamin D-deficient women exhibited higher prepregnancy body mass index (BMI), prepregnancy weight, midpregnancy weight, weight gain, blood pressure (systolic [SBP] and diastolic [DBP]), hemoglobin A1C (HbA1C), triglycerides, fasting insulin, and HOMA-β compared with individuals without a deficiency.

In addition, the prevalences of postpartum glucose intolerance and overt diabetes were 44.8% and 4.9%, respectively. “Women with vitamin D deficiency at midpregnancy had a higher prevalence of postpartum glucose intolerance than did those without vitamin D deficiency (48.7% vs 32.1%; P = .011),” the researchers said.

After adjusting for maternal age, prepregnancy BMI, weight gain, blood pressure (SBP and DBP), family history of diabetes, and season, the researchers found:

• Vitamin D level was negatively correlated with HbA1c antepartum (P = .001) and postpartum (P = .047)
• HOMA-β was positively correlated with serum 25(OH)D level postpartum (P = .035)
• The risk of postpartum glucose intolerance was still 2 times (95% CI, 1.13-3.55) higher in women with vitamin D deficiency than in those without vitamin D deficiency (P= .018)

Due to the fact that in Korea, around 90% of women are not vitamin D sufficient, the researchers note these results are not generalizable across ethnic groups and large prospective studies are needed to confirm results.

However, “vitamin D deficiency at midpregnancy is associated with an elevated risk of postpartum glucose intolerance in women with GDM,” the researchers said.

Reference

Kim K, Park SW, Cho Y, et al. Vitamin D deficiency at mid-pregnancy is associated with a higher risk of postpartum glucose intolerance in women with gestational diabetes mellitus. Endocrinol Metab (Seoul). 2020;35(1):97-105. doi: 10.3803/EnM.2020.35.1.97.