When should pregnant women take folic acid?

By Annie Harrison-Dunn

- Last updated on GMT

Pre-conception folic acid supplementation may reduce preterm birth risk by 8% and small-for-gestational-age birth risk by 19% compared to those not using supplements. Photo credit: iStock.com
Pre-conception folic acid supplementation may reduce preterm birth risk by 8% and small-for-gestational-age birth risk by 19% compared to those not using supplements. Photo credit: iStock.com

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Taking folic acid supplements pre-conception may lower the risk of preterm birth and small-for-gestational-age, but post-conception may be too late to have an effect, according to research in 240,954 pregnant women.

The researchers from the Zhejiang University and Jiaxing Maternity and Child Health Care Hospital in China, the University of Cambridge School of Clinical Medicine in the UK and Harvard School of Public Health in the US used data from the Jiaxing Birth Cohort, within which prevalence of preterm birth and small-for-gestational-age birth was 3.48 and 9.2%, respectively.

They found pre-conception folic acid supplementation was associated with an 8% lower risk of preterm birth and 19% lower risk of small-for-gestational-age birth compared with those not using the supplements.

Yet no significant association with either outcome was seen when folic acid supplementation was started post-conception.

This was important given the study also revealed supplementation was started more often post-conception (14%) than preconception (10%).

Overall prevalence of folic acid supplementation was 24.9%.

However this differed significantly depending on year of recruitment.

Supplementation prevalence ranged from 7.6 to 24.2% during the 11 years from 1999 to 2009 and increased to 48.7% in 2010, 67.2% in 2011 and 64.6% in 2012.

The researchers said this was probably a result of government health initiatives in China. Since late 2009 rural Chinese women of child-bearing age were given free folic acid supplements of 400 mg per day.

“The initiation of the new policy may have increased the health consciousness of women of child-bearing age and reduced other risk factors of adverse pregnancy outcomes, thereby attenuating or even eliminating the inverse association of folic acid supplements with small-for-gestational-age birth,”​ they wrote in the British Journal of Nutrition.

The researchers said the impact of maternal folate status on infant neural tube defects (NTD) and other congenital disorders – for which there is an approved health claim in the EU​ - ​was now well accepted.

However, the association of folate supplementation with other pregnancy outcomes like preterm birth and small-for-gestational-age birth were still “inconclusive”.

A global perspective

The results for pre-conceptional supplementation were in line with past cohorts, yet were less pronounced.

A 2009 US cohort of 34,480 women​ who pre-conceptionally started folic acid supplementation, saw a 50–70% reduction in the incidence of early spontaneous preterm birth.

Meanwhile this year a Dutch cohort of 6353 women​ who started pre-conceptionally taking the supplements showed a 60% reduction of small-for-gestational-age birth risk compared with non-users.

This latest study was something of a first within Chinese populations however.

“The present study has provided, so far, the largest sample size to examine the relationship between folic acid supplementation and preterm birth (PTB) and small-for-gestational-age (SGA) birth in a Chinese setting. The present results provide important and valuable information for the prevention of PTB and SGA in the Chinese populations,” ​they wrote.

Right timing 

Speaking with NutraIngredients in July, the Irish public health body Safefood said a key challenge in getting women to take folic acid supplements preconception​ was that many pregnancies were unplanned.

Discussing NTD specifically, Safefood's chief nutrition specialist Dr Marian Faughnan said the issue needed to become a matter of women’s health generally, not just women looking to start a family.

This would ensure enough folic acid (vitamin B9) could build up in the system.

Women need 200 micrograms (mcg) of folic acid per day ordinarily, which can be achieved easily with a healthy diet. Yet for pregnant women this jumps up to 600 mcg, which would take something like 1.2 kg of broccoli a day to achieve.

Source: British Journal of Nutrition

Published online ahead of print, doi:10.1017/S0007114515004663

“Pre-conceptional intake of folic acid supplements is inversely associated with risk of preterm birth and small-for-gestational-age birth: a prospective cohort study”

Authors: J. S. Zheng, Y. Guan, Y. Zhao, W. Zhao, X. Tang, H. Chen, M. Xu, L. Wu, S. Zhu, H. Liu, T. Huang and D. Li

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