2.3. Blood Sample Collection and Processing
LATE PREGNANCIES
Maternal blood samples were collected at two time points: at enrollment at 10–18 weeks of gestation and at 32–38 weeks of gestation. The serum 25-hydroxyvitamin D 25(OH)D level (termed as the vitamin D level hereafter) was measured in both samples using the DiaSorin LIAISON method (a chemiluminescence assay) at the Channing Division of Network Medicine, Brigham and Women’s Hospital (Boston, MA, USA). All the 118 women who provided a stool sample in the third trimester of pregnancy provided a blood sample at the first time point (yielding a baseline vitamin D level), and 114 of them also provided one at the second time point (yielding a final vitamin D level). Therefore, we have blood samples to analyze the change in vitamin D level between the early and late pregnancies of 114 women; 59 of them were in the treatment group, and the remaining 55 were in the placebo group. 