Prevalence of vitamin B-12 insufficiency during pregnancy and its effect on offspring birth weight: a systematic review and meta-analysis

Abstract

Background: Vitamin B-12 and folate are micronutrients essential for normal embryogenesis. Vitamin B-12 insufficiency in pregnancy is high in certain parts of the world, such as India, and although this has been linked to low birth weight (LBW) in these populations, the relation between vitamin B-12 and birth weight (BW) elsewhere is unknown. Objectives: We performed a systematic review to assess 1) the worldwide prevalence of vitamin B-12 insufficiency in pregnancy and 2) its association with BW. Design: A search of 5 electronic databases was performed to identify eligible articles. Random-effects meta-analysis was conducted according to geographic regions and pregnancy trimesters for the prevalence subreview and by categorical measures of BW. Results: A total of 57 and 23 articles were included for the prevalence and BW subreviews, respectively. The pooled estimates of vitamin B-12 insufficiency were 21%, 19%, and 29% in the first, second, and third trimesters, respectively, with high rates for the Indian subcontinent and the Eastern Mediterranean. The large heterogeneity between studies was partially addressed by creating a standardized score for each study (mean vitamin B-12 insufficiency O cutoff value), which internally corrected for geographic region, trimester, and assay type. Twelve of the 13 longitudinal studies included showed a decrease in mean or median vitamin B-12 across trimesters. Pooled analysis showed nonsignificantly lower maternal vitamin B-12 concentrations in LBW than in normal-BW infants and higher odds of LBW with lower vitamin B-12 values (adjusted OR: 1.70; 95% CI: 1.16, 2.50), but studies from India largely contributed to the latter. Conclusions: Our review indicates that vitamin B-12 insufficiency during pregnancy is common even in nonvegetarian populations and that concentrations of vitamin B-12 decrease from the first to the third trimester. There is no consistent association between vitamin B-12 insufficiency and LBW. However, given the long-term risks of LBW, this observation warrants further cohort studies and randomized controlled trials.Am J Clin Nutr 2016;103:1232-51.

The Impact of Third Trimester Maternal Serum Vitamin B12 and Folate Status on Fetal Birth Weight. Is Maternal Serum Homocysteine a Predictor of Low Birth Weight Infants?

“…Recently Sukumar et al [7] reported that the pooled estimate of maternal vitamin B12 insufficiency during pregnancy across all three trimesters were 21%, 19%, and 29% respectively. The effects of maternal B12 level on birth weight is still controversial, our results showed that the mean maternal vitamin B12 level in mothers with LBW [38] reviewed 29 articles and they concluded that although there is an association between low maternal vitamin B12 and intrauterine growth retardation, but no studies have definitively determined the cut off value for serum vitamin B12 level during pregnancy.…”

“…However, several studies did not detect any association between maternal vitamin B12 levels and fetal growth restriction [3] [42]. Recently a systematic review and meta analysis done by Sukumar et al [7] they reviewed 57 reviews and 23 articles, showed non significantly lower maternal vitamin B12 concentrations in LBW than in ABW infants but higher odds of LBW with lower vitamin B12 values (adjusted OR: 1.70; 95% CI: 1.16, 2.50), and concluded that there was no significant effect of low maternal vitamin B12 level and LBW. The authors concluded also that the lack of an association might have been due to an overall low vitamin B12 status or, it would be difficult to demonstrate a nutrient effect in these women who were vitamin B12 replete.…”

“…In a recent systemic review, cobalamin insufficiency reported to be common among pregnant women in all trimesters by 20% -30% [7].…”

“…Most homocysteine is catabolised to cystathionine by cystathionine-h-synthase. Another pathway to be regenerated into methionine by methionine synthase where vitamin B12 and folate are necessary cofactors for the conversion of homocysteine to methionine, required for the synthesis of phospholipids and neurotransmitters [7].…”

Do the benefits of folic acid fortification outweigh the risk of masking vitamin B12deficiency?

“…Fortification undoubtedly reduces neural tube defects. But vitamin B 12 deficiency in pregnancy is also common in many countries29 and is also a risk factor for neural tube defects. Such defects attributable to B 12 deficiency have tripled in Canada, which has folate fortification 30.…”