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Folate supplementation and twin pregnancies
Stein Emil Vollset1, Håkon K Gjessing, Anne Tandberg
1Department of Public Health and Primary Health Care, Section for Epidemiology and Medical Statistics, Locus for Registry Based Epidemiology, University of Bergen, Bergen, Norway. vollset@uib.no
Epidemiology (Cambridge, Mass.)
|February 11, 2005
Summary
Folic acid supplementation before pregnancy is not linked to an increased risk of twin births. Initial concerns were due to confounding factors, particularly in vitro fertilization (IVF) pregnancies.
Area of Science:
- Reproductive Health
- Maternal-Fetal Medicine
- Nutritional Epidemiology
Background:
- Folate supplementation is recommended globally to prevent neural tube defects.
- Fortification of flour with folate is a common public health strategy.
- Monitoring potential adverse effects of folate, such as impacts on twinning, is crucial.
Purpose of the Study:
- To investigate the association between preconceptional folate intake and the risk of twin pregnancies.
- To determine if any observed association is confounded by factors like in vitro fertilization (IVF).
Main Methods:
- A retrospective population-register based study of 176,042 births in Norway (1998-2001).
- Data on folate and multivitamin use collected from mandatory birth notification forms.
- Analysis adjusted for maternal age and parity, with specific consideration for IVF pregnancies.
Main Results:
- An initial observed increased risk of twin pregnancies with preconceptional folate use (OR=1.59) was largely explained by confounding with IVF.
- After excluding known IVF pregnancies and accounting for underreporting, the association between folate and twinning was no longer significant (OR=1.02).
- Weak associations for multivitamins during pregnancy were noted but potentially explained by reverse causation.
Conclusions:
- The apparent link between preconceptional folate and twin pregnancies is primarily due to confounding by IVF.
- This study found no evidence to support an association between preconceptional folate supplements and an increased risk of twinning after accounting for IVF and underreporting.