Prevalence of vitamin B12 deficiency and associated factors in pregnant Spanish women.

Vitamin B12 deficiency remains a public health concern, even in developed countries. This study aimed to determine the prevalence of vitamin B12 deficiency during the first and third trimesters of pregnancy and identify associated risk factors in healthy pregnant women from the Spanish Mediterranean region. This longitudinal, community-based study was nested within the ECLIPSES randomized controlled trial and examined cross-sectionally at two time points, including 670 and 421 women in the first and third trimester, respectively. Serum vitamin B12 and red blood cell (RBC) folate concentrations were measured, and sociodemographic, dietary, obstetric, and lifestyle data were collected. Vitamin B12 status was classified using WHO cutoff points for pregnant women: deficiency (<200 pg/mL) and marginal deficiency (200-300 pg/mL). In the first trimester, vitamin B12 deficiency and marginal deficiency rates were 4 percent and 28 percent, respectively, increasing to 19 percent and 45 percent by the third trimester. Higher socioeconomic status (OR = 0.625, p = .011) and RBC folate levels (OR = 0.998, p < .001) reduced the risk of marginal deficiency in the first trimester, while a higher body mass index (BMI) increased it (OR = 1.046, p = .029). In the third trimester, only BMI was linked to an elevated risk of deficiency (OR = 1.102, p = .015). No significant associations were found with vitamin B12 deficiency in the first trimester or marginal deficiency in the third trimester. Marginal vitamin B12 deficiency and deficiency are associated with modifiable risk factors, including socioeconomic status, overweight, and RBC folate, whose relevance varies by trimester, highlighting the importance of monitoring during prenatal care.