Assessment of blood one-carbon metabolism indexes during mid-to-late pregnancy in 397 Chinese pregnant women

Objectives One-carbon metabolism (OCM) significantly influences fetal growth and neurodevelopment through transferring methyl group to biomolecules, during which folate, methionine, choline and betaine function as methyl donor nutrients, while vitamin B 2 , B 6 , B 12 function as enzyme cofactors, and homocysteine (Hcy) and S-adenosyl methionine (SAM) are functional metabolites. This study aimed to assess blood OCM index levels and explore their relationships among Chinese pregnant women. Methods Data were obtained from the baseline of the Mother–Child Nutrition and Health Cohort Study. Pregnant women, voluntarily recruited from September 2020 to June 2022 during antenatal examinations in five Chinese cities at 24–32 gestational weeks, provided fasting venous blood samples. Measurements included RBC and serum folate, serum vitamin B 2 , B 6 , B 12 , choline, betaine, methionine, total Hcy (tHcy), and plasma SAM. Sociodemographic characteristics and pregnancy-related conditions were collected via a self-designed questionnaire. Results Of 397 participants, 82.6% were in mid-pregnancy (24–27 gestational weeks) and 17.4% were in late-pregnancy (28–32 gestational weeks). Serum folate, vitamin B 6 , and B 12 deficiencies were 2.5, 1.3, and 8.3%, respectively. Elevated tHcy (≥10 μmol/L) was observed in 1.8% of pregnant women. Elderly pregnant women (aged 35 and above) exhibited significantly lower serum methionine levels ( p 0.05), while multiparous women had lower RBC folate levels ( p 0.05), and lower serum methionine and vitamin B 12 levels ( p 0.10, not statistically significant). Partial correlation analysis revealed positive associations between RBC folate and cofactor vitamin B 12 ( r = 0.244, p 0.05) in the folate cycle, as well as significant correlations between two methyl donor paths serum folate was significantly related to serum choline ( r = 0.172) and betaine ( r = 0.193). As functional biomarkers of OCM, serum tHcy exhibited negative associations with RBC folate ( β = −0.330, p 0.05) and vitamin B 6 ( β = −0.317, p 0.05), and plasma SAM displayed a positive association with serum betaine ( β = 0.610, p 0.05), while negatively associated with serum vitamin B 6 ( β = −0.181, p 0.05). Conclusion The blood OCM exhibited imbalances during mid-to-late pregnancy, characterized by lower levels of folate, vitamin B 6 , and B 12 , alongside elevated tHcy levels. Adequate folate and vitamin B 6 emerged as significant predictors of lower tHcy levels. Additionally, serum betaine showed a positive correlation with plasma SAM. This suggests the importance of not only ensuring sufficient folate but also optimizing other OCM-related nutrients throughout pregnancy.