Observational Study of Third-Trimester Vitamin D3 Supplementation and Implications for Mothers and Neonates at Term.

Objective: To determine 25-hydroxyvitamin D (25OHD) levels in pregnant women at 28 weeks and supplement based on these levels and check maternal and neonatal levels after delivery at term.

Design: This is a prospective observational study wherein pregnant women aged 18-35 years received cholecalciferol from 28 weeks till delivery at term. Women with 25OHD levels ≥ 75 nmol/L received 12.5 μg/day, those with levels 50-74.9 nmol/L received 100 μg/day and those with  levels ≤ 49.9 nmol/L received 1500 μg/week.

Results: Of 555, 532 women (95.8%) completed the study. Of 532, 77 (14.5%) women had 25OHD ≥ 75 nmol/L at 28 weeks; 34/77 (44.15%) became deficient at term, and the mean 25OHD reduced from 99 ± 29.9 to 77 ± 30.4 nmol/L ( < 0.0001). One hundred and seventy-one women had 25OHD 50-74.9 nmol/L at 28 weeks; in 99 (57.89%), levels normalised at term, and mean 25OHD increased from 60.5 ± 7.5 to 78.2 ± 21.9 nmol/L ( < 0.0001). Two hundred and nineteen women had 25OHD 25-49.9 nmol/L at 28 weeks; in 135 (61.64%), levels normalised at term, and mean 25OHD increased from 36.6 ± 7.5 to 83.3 ± 32.7 nmol/L ( < 0.0001). Sixty-five women had 25OHD < 25 nmol/L at 28 weeks; In 39 (60.94%), levels normalised at term, and the mean 25OHD increased from 17.9 ± 5 to 80.6 ± 34.1 nmol/L ( < 0.0001). Seven neonates (1.3%) had cord blood ionised calcium values < 1 mmol/L, and all these had 25OHD < 50 nmol/L (mean 22.2 ± 2.5 nmol/L).

Conclusions: Standard 12.5 μg/day supplementation in women with normal 25OHD levels at 28 weeks leads to deficiency in 44% women by term. Cholecalciferol in doses of 100 μg/day and 1500 μg/week leads to a significant increase in 25OHD levels in vitamin D-deficient pregnant women though nearly 40% may still have deficient levels at term along with their newborns. Only 1.3% of newborns had hypocalcaemia.