This randomized, placebo-controlled trial in Thai pregnancy is conducted. The study aims to determine whether vitamin D3 1,800 IU/d supplementation in lactating mother improves vitamin D status of breastfed infant.

Vitamin D deficiency in pregnancy increases risk of gestational diabetes mellitus, pre-eclampsia, preterm birth, low birth weight and cesarean section. To against these adverse events, vitamin D supplementation in pregnancy and lactation is recommended, but dose ranges are varied. Then, this study is carried out in lactating mothers and their breastfed infants with maternal 25 Hydroxy-vitamin D (25OHD) levels of 10-30 ng/ml in third trimester. Subjects are divided into 2 groups, one is randomly assigned to 1,800 IU/d compared with maternal and infant controls receiving placebo. Maternal serum 25OHD and milk VitD will be measured by LC-MS/MS during lactation, and on cord blood at 6 weeks breastfed infants. This study is submitted for ethical consideration by relevant Ethics committee.

Inclusion Criteria:

• Pregnant Thai women and intends to deliver at Rajavithi Hospital
• Insufficient Vitamin D levels (25(OH)D < 30ng/ml)
• Gestational age at birth and no complications

Exclusion Criteria:

• Age < 18 years old
• Unintended to deliver at Rajavithi Hospital
• Insufficient Vitamin D levels (25(OH)D < 10ng/ml)