This cross-sectional study was conducted at the Saad Abuelela Maternity Hospital in Khartoum, Sudan, from October 15 to 30, 2021.
Inclusion Criteria
Women presented to the labor room with a term birth (37‒41weeks of gestation) of a single, alive newborn were included in the study.
Exclusion Criteria
Women with uncertain dates, preterm birth (< 37 weeks of gestation), multiple pregnancies, intra-uterine fetal death, a baby with one or more congenital anomalies, diseases such hypertension, diabetes mellitus and antepartum hemorrhage or any other chronic disease and those taking any drugs were excluded.
After obtaining their informed consent, the sociodemographic, medical and obstetric data of the subjects were gathered and recorded via a questionnaire (age, parity, gestational age, antenatal attendance, education level and employment). Gestational age was calculated using a combination of the dates of the subject’s last menstrual period and the early pregnancy ultrasound.
Following this, five milliliters of blood were taken from the maternal subjects and umbilical cords and collected in plain tubes. These were immediately labeled and allowed to clot at room temperature. The blood samples were then centrifuged and stored at -20°C before being assessed for 25-(OH)D levels using an enzyme-linked immunosorbent assay as per the manufacturer’s instructions (Euroimmun, Lubeck, Germany).
Sample Size Calculation
The sample size (90 samples from the mothers and umbilical cords) was calculated based on our previous report regarding the desired level of serum 25-(OH)D (15.0 ng/mL) in pregnant Sudanese women [7]. We assumed that the umbilical cord level of 25-(OH)D would be higher (18.0 ng/mL) than the maternal level based on recent reports about the maternal and umbilical cord levels of 25-(OH)D [8, 9]. We assumed a mean difference of 3 ng/mL between the maternal and umbilical serum 25-(OH)D concentrations. The sample size (90 samples) was determined to achieve a power of 80% and a precision of 5%.
Statistics
All statistical analyses were performed using the Statistical Package for the Social Sciences for Windows version 22.0 (SPSS Inc., Chicago, Illinois, USA). Continuous data (25-(OH)D) were checked for normality using the Shapiro–Wilk test. The 25-(OH)D levels of the two groups (maternal and umbilical cord) were compared using the Mann–Whitney U test. Spearman’s correlations were performed between the maternal and umbilical cord 25-(OH)D levels. P-values < 0.05 were considered significant.