Endocrine Abstracts

Objective: Vitamin D has a pleiotropic effect on the human body. Besides its classical function as a regulator of calcium and phosphorus metabolism, it influences the secretion of other hormones, modulates the immune response and regulates cell proliferation and differentiation. Because women in twin pregnancies have higher metabolic needs, it can be expected that they might have higher risk of vitamin D deficiency.

Aim of the study and method: The aim is to analyze the serum and cord blood concentrations of vitamin D metabolites in women in twin pregnancies with the use of liquid chromatography-tandem mass spectrometry (LC-MS). Until the submission of this abstract (January 2022) 15 maternal and 30 cord blood samples were tested. We have collected data on supplementation and dietary intake questionnaires.

Results: The mean maternal age was 34.1 years (±3.5). The delivery took place at an average 34.8 week of pregnancy (±3.3). All patients supplemented vitamin D in doses ranging from 200-4000 international units per day. The median concentration of total 25-hydroxyvitamin D (25(OH)D) in maternal serum was 43.9 ng/ml (interquartile range [IQR] 42.0-54.1). Its deficiency was found in one patient. Elevated vitamin D levels were found in 36.4% of the mothers (maximum 73.6 ng/ml). The median concentration of 25(OH)D in cord blood was 25.2 ng/ml (IQR 20.1-28.8). Maternal and cord blood levels were highly correlated (r=0.58). However, in each case, 25(OH)D level in the cord blood was lower than in the serum of corresponding mother (difference ranging from 7.1-48.2 ng/ml). In each pair of twins cord blood 25(OH)D concentrations were similar (differences: minimum 0.2, maximum 5.8, mean 2.2 ng/ml). In the described group, 25(OH)D levels in mothers were also determined by the commonly used in clinical practice chemiluminescent immunoassay (CLIA). The 25(OH)D levels obtained using the LC-MS method were significantly higher (median 43.9 ng/ml, IQR 42.0-54.1), than in case of CLIA (median 31.3 ng/ml, IQR 23.4-40.2;P=0.003). The differences in individual patients ranged from 5.4 ng/ml up to 36.7 ng/ml. These finding seem particularly important in terms of clinical decision making.

Conclusions: In the studied group of women in twin gestation that supplemented vitamin D, low prevalence of its deficiency determined by LC-MS was found. Maternal and cord blood levels of 25(OH)D were highly correlated. There are large discrepancies in the 25(OH)D concentrations obtained with LC-MS compared to CLIA in maternal samples.