Researchers have found that both excessive and reduced folate levels during pregnancy raise the risk of congenital heart defects.

Congenital heart defects are structural problems with the heart that occur during pregnancy when the baby's heart does not develop properly. It is the most common birth defect, that affects around 2.3% of births. The most common types include septal defects (holes in the heart), heart valve defects (problems with the valves that control blood flow), and defects in the large blood vessels that carry blood to and from the heart.

Folate, also known as vitamin B-9, is crucial for healthy cell growth and fetal development. It naturally occurs in dark green leafy vegetables, beans, peas, nuts, and fruits like oranges, lemons, bananas, melons, and strawberries. The synthetic version of folate called folic acid, is commonly recommended during pregnancy to prevent birth defects, particularly neural tube defects.

Researchers of the latest study who examined the association between maternal serum folate levels and congenital heart defect risk in offspring noted a U-shaped association, meaning both low and high maternal folate were linked to a higher risk of heart defect. The study observed that vitamin B12 deficiency and increased homocysteine levels are also relevant factors for increasing the risk.

The findings were based on analysis of blood samples of mothers of 129 children with congenital heart defects and 516 without. The folate, vitamin B12, and homocysteine levels of the maternal blood samples were taken around the 16th week of pregnancy. Based on their folate levels, mothers were divided into three groups: low (bottom 25%), middle (50%), and high (top 25%).

The analysis revealed that mothers in the low folate group have over three times the risk of having a child with a congenital heart defect compared to those in the middle group. Meanwhile, those in the high folate group also had an increased risk, with 1.81 times the odds of congenital heart defects.

Children born to mothers with both a vitamin B12 deficiency and low folate levels had a sevenfold higher risk of congenital heart defects. In the high folate group, a B12 deficiency was linked to a sixfold increase in the risk.

Additionally, elevated homocysteine levels combined with low folate were associated with nearly nine times the odds of developing congenital heart defect while the high folate group showed a sevenfold higher risk. Homocysteine is an amino acid involved in a critical metabolic pathway that is essential for cellular functions including DNA synthesis, repair, and methylation.

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