Association of 25(OH)-Vitamin D3 Serum Concentrations and Vitamin D Receptor Gene Variants with the Risk of Idiopathic Spontaneous Preterm Birth in the Croatian Population

Preterm birth (PTB) forms a heterogeneous group with possible genetic predisposition. 25(OH)-vitamin D3 plays a significant role during implantation, placentation, and the maintenance of normal pregnancy. The aim of our research was to examine whether FokI, Cdx2, and ApaI <i>VDR</i> gene variants, as well as serum concentrations of 25-hydroxy25(OH)-vitamin D3 in women and their newborns, might be predisposing factors for idiopathic spontaneous preterm birth. The patient group consisted of 44 pairs of women with ISPTB and their children, and the control group consisted of 44 pairs of women who delivered at term and their children. At the time of delivery, peripheral blood was collected from every woman, and after newborn delivery, umbilical cord blood was collected. For genotyping of the rs2228570 C/T, rs11568820 G/A, and rs7975232 T/G SNPs, a combination of polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) was used. Serum concentrations of 25(OH)-vitamin D3 were determined using high-performance liquid chromatography (HPLC). There were no statistically significant differences in the frequencies of <i>VDR</i> genotypes and alleles between women with ISPTB and control women. There was a statistically significant difference in the distribution of <i>VDR</i> Cdx-2 (rs11568820) genotypes between preterm-born children and controls, with the GG genotype and G allele being more prevalent among patients than controls (<i>p</i> < 0.001). There were no statistically significant differences in mean values between women with ISPTB and control women, nor between preterm and full-term newborns, although the 25(OH)-vitamin D3 concentrations in preterm-born children were lower than in controls. Furthermore, there was a statistically significant correlation in 25(OH)-vitamin D3 concentrations between mothers and children both in the patient and in the control groups (b = 0.771, <i>p</i> < 0.001). The results of our study demonstrate a notable association between the <i>VDR</i> Cdx2 gene polymorphism and idiopathic spontaneous preterm birth (ISPTB) in a Caucasian population, but because of the small number of participants, further research is needed.