The Effect of Vitamin D Supplementation in Overweight and Obese Pregnant Women

The effects of vitamin D supplementation on pregnancy outcomes and metabolic status of overweight and obese pregnant women remain uncertain. In particular, the dosage of vitamin D supplementation has not been defined in this high risk group of women. This study aims to examine whether oral supplement of vitamin D3 (cholecalciferol) in total dosage of 800 IU(prenatal multivitamin containing 400 IU vitamin D3 + 400 IU vitamin D3 alone) given to overweight and obese pregnant women since early pregnancy until delivery can improve maternal and neonatal outcomes, compared with those given prenatal multivitamin containing 400 IU vitamin D3 supplementation, a commonly given antenatal supplement in Singapore. The investigators' hypothesis is that higher dose vitamin D supplementation would lead to better outcomes in overweight and obese pregnant women. The investigators will conduct a two-arm, parallel non-blinded randomized controlled trial. Women with body mass index ≥25kg/m2 will be randomly assigned into groups with a 1:1 randomization ratio, receiving either 800 or 400 IU vitamin D3 supplementation. The study will be conducted at the antenatal clinics, KK Women's and Children's Hospital, Singapore. Measurements of serum 25-hydroxyvitamin D (25OHD), lipid profile and lifestyles information will be taken for all women at baseline (≤16 weeks gestation) and after three months of intervention (26-30 weeks gestation). All women will continue with the vitamin D3 supplementation until delivery. Primary outcomes include levels of maternal serum 25OHDconcentration and lipid profile at 26-30 gestation weeks as compared with the controls, adjusting for baseline measurements. Secondary outcomes include preeclampsia, gestational hypertension, gestational diabetes, glycaemic levels, caesarean section, gestational weight gain, preterm birth, low birth weight and small-for-gestational-age. This study will fill up the gap of knowledge regarding the role of vitamin D supplementation on pregnancy outcomes and metabolic status in overweight and obese pregnant women.

Inclusion criteria

• Gestation ≤16weeks (16 weeks + 6 days) upon intervention
• Pre-pregnancy BMI ≥25 kg/m2
• Aged 21-45 years
• Willing and able to provide written, informed consent

Exclusion criteria

• Having current or past hypo/hyperparathyroidism, hypercalciuria, hypercalcemia or osteomalacia
• History of renal disease (including kidney stones and etc.), liver dysfunction, tuberculosis or sarcoidosis
• Pre-existing diabetes mellitus or chronic hypertension
• Taking lipid-lowering medicine
• Gestational diabetes (as confirmed by oral glucose tolerance test) or gestational hypertensive disorder
• Multiple pregnancy