The relationship between vitamin D deficiency and insulin resistance during pregnancy

Background. Vitamin D insufficiency is associated with metabolic complications during pregnancy, including insulin resistance. Physiological processes during pregnancy contribute to increased insulin resistance, which, in turn, is the main symptom of gestational diabetes. There is evidence that excessive weight gain during pregnancy negatively affects the concentration of 25-hydroxyvitamin D (25(OH)D). The aim of the study was to determine the effect of vitamin D insufficiency and deficiency during pregnancy on the occurrence of insulin resistance in the third trimester against the background of excessive weight gain. Materials and methods. The prospective study included 65 pregnant women with a gestation period of up to 20 weeks (on average 17 weeks). At the initial stage, a survey (body weight before pregnancy), and a clinical examination were conducted. Subsequent examinations were carried out in the second (20 weeks) and third (28 weeks) trimesters. Weight gain during pregnancy was calculated as the difference in body weight (between the third and second trimester) divided by the number of gestational weeks in that interval, following the Institute of Medicine guidelines. Gestational weight gain was classified as excessive, taking into account pre-pregnancy body mass index. Predicting the probability of insulin resistance (according to the HOMA-IR) was assessed by the dynamics of body weight gain. Results. Median 25(OH)D in the second and third trimesters of pregnancy was 23 and 24 ng/ml, respectively. Vitamin D insufficiency (25(OH)D < 30 ng/ml) was observed in at least one of the trimesters in 47 (72.3%) pregnant women, while the permanent nature of vitamin D insufficiency was noted in 36 (55.4%) cases. Vitamin D deficiency was established in 8 (12.3%) pregnant women in the second trimester. Excessive weight gain during pregnancy was observed in 34 (52.3%) women. Insulin resistance was determined in 31 (47.7%) pregnant women in the third trimester. The median of immunoreactive insulin concentration and HOMA-IR was higher among women with vitamin D deficiency. Conclusion. Vitamin D insufficiency is associated with insulin resistance in the third trimester of pregnancy, which depends on excessive gestational weight gain.