To establish reference intervals (RIs) for red blood cell (RBC) folate, vitamin B12, homocysteine, and 5-methyltetrahydrofolate (5-MTHF) during the first trimester of pregnancy among women in the Qingdao region, stratified by age, body mass index (BMI), and total folate intake categories. A cross-sectional study was conducted involving 2,911 pregnant women (9 to 13+ 6 weeks of gestation) recruited during their first prenatal visit in Qingdao from February 2023 to April 2024. Fasting venous blood samples were collected, and biomarker concentrations were measured using ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) and chemiluminescence immunoassay techniques. Data analysis followed the CLSI C28-A3 guidelines, with subgroup stratification by age, BMI, and total folate intake. The biomarker concentrations are reported as median (interquartile range): Vitamin B12: 525.00 (422.50,663.50) pg/mL; RBC folate: 421.41 (327.14,558.14) ng/mL; homocysteine:6.3 (5.5,7.2) µmol/L, and 5-MTHF: 27.78 (19.28,39.24) ng/mL. Significant age-related and BMI-associated differences in biomarker levels were identified (P < 0.05). Age and BMI related differences in biomarker concentrations were mainly reflected in median values. Women aged ≥ 35 years had higher median levels of vitamin B12 (536.00 vs. 520.00 pg/mL), RBC folate (444.19 vs. 411.16 ng/mL), and 5-MTHF (28.38 vs.27.46 ng/mL), but lower median homocysteine (6.2 vs. 6.3 µmol/L) compared with women < 35 years (P < 0.05). Across BMI categories (underweight, normal weight, overweight, obese), median vitamin B12 varied (584.88, 578.54, 537.52, 532.26 pg/mL, P < 0.001), while RBC folate showed a progressively increasing trend (441.03, 457.18, 477.69, 483.66 ng/mL, P = 0.003). Median homocysteine (6.4, 6.2, 6.3, 6.4 µmol/L) and 5-MTHF (30.61, 30.80, 29.67, 27.42 ng/mL) also differed significantly across BMI groups (P < 0.001). Furthermore, biomarker concentrations demonstrated clear trends across quartiles of total folate intake: RBC folate, vitamin B12, and 5-MTHF increased progressively from Q1 to Q4, while homocysteine decreased (all P < 0.001). This study characterized the distribution of RBC folate, vitamin B12, homocysteine, and 5-MTHF concentrations in early pregnancy (9–13+ 6 weeks) and established RIs across different age, BMI, and total folate intake subgroups in Qingdao population. These findings provide valuable reference data for clinicians and laboratory researchers.
Ding et al. (Wed,) studied this question.