This prospective nested case-control study aims to examine the effects of blood vitamin B levels in first-trimester pregnant women on the pregnancy outcomes

Folate deficiency can cause severe adverse pregnancy outcomes, such as neural tube defects. Effective folate functioning requires essential metabolic interactions with other B vitamins including vitamin B2, vitamin B3, vitamin B6, and vitamin B12, which can also influence pregnancy outcomes independently. For example, animal and family studies have identified that niacin (B3) deficiency can lead to congenital malformations. However, how folate and related B-vitamin levels interact with each other while affecting various pregnancy outcomes including abortion, birth defects, pregnancy complications, etc. is unclear. Besides, folate levels in previous studies were mostly measured in plasma which are easily influenced by dietary factors, instead of red blood cell folate which can reflect the long-term status. Moreover, the difference in the risk of neural tube defects across a range of maternal red blood cell folate concentrations has been largely ignored. Using data of pregnant women recruited at Beijing Obstetrics and Gynecology Hospital from December 2020 to December 2021, this case-control study aims to examine the association of folate and related B-vitamin levels in first-trimester blood samples (plasma and red blood cell) with pregnancy outcomes, particularly the association between niacin deficiency and birth defects.

Inclusion Criteria:

• Pregnant women with 6-13(+6 days) gestational weeks
• Resided in Beijing in the past year
• Pregnant women who intend to have antenatal examinations and delivery at Beijing Obstetrics and Gynecology Hospital
• Pregnant women who are willing to participate in this study with informed consent

Exclusion Criteria:

• Women with Hepatitis B, syphilis, HIV/AIDS and other infectious diseases.

all pregnant women recruited in the birth cohort of Beijing Obstetrics and Gynecology Hospital between 2020.12 to 2021.12