When couples are planning a pregnancy, most nutritional advice is directed toward the mother-to-be: Start preparing before conception. Take folic acid. Eat well. But a new study suggests that a father's nutritional status may also deserve attention.

Researchers in China found that higher levels of vitamin B12 in both prospective mothers and fathers before conception are associated with a lower likelihood of birth defects in their children. The study also reported that women with higher levels of red blood cell folate during early pregnancy had lower predicted rates of birth defects. The findings add to growing evidence that preparing for a healthy pregnancy may be a two-person undertaking.

Prenatal and preconception health is not solely a woman's responsibility.

The study was led by researchers at the Children's Hospital of Fudan University in Shanghai. It examined whether low levels of two important nutrients, vitamin B12 and folate, around the time of conception, led to birth defects in offspring.

The researchers studied two groups. One included 3,032 couples who had blood samples taken within four months before conception. The second included 17,765 women whose blood was tested by the fourth month of pregnancy or earlier.

Researchers calculated participants' vitamin B12 and red blood cell folate, a measure that reflects longer-term folate status. The team then tracked pregnancies and identified birth defects among live births, still births and pregnancies that ended because fetal abnormalities were detected.

The results showed a consistent association between higher B12 levels before conception and a lower rate of birth defects. Among women, the predicted prevalence of birth defects fell from 49.6 cases per 1,000 pregnancies among those with the lowest preconception B12 levels to 16.2 per 1,000 among those with the highest levels. The study also noted a benefit associated with adequate maternal folate levels after conception.

Fathers showed a similar pattern. Predicted rates declined by roughly half — from 55.5 to 24 cases per 1,000 pregnancies across the lowest to highest B12 categories.

Higher levels of vitamin B12 in both prospective mothers and fathers before conception are associated with a lower likelihood of birth defects in their children.

These findings do not prove that taking B12 supplements will prevent birth defects. This was an observational study that found an association or connection between higher folate and B12 levels and a reduced risk of birth defects. The study did not test whether supplements directly caused better outcomes. Still, the results point towards something that has received comparatively little attention: A father's health before conception may influence a pregnancy's outcome.

That idea represents a shift from the traditional focus on maternal nutrition alone. Folic acid supplementation for women before and during early pregnancy is already well established as a way to reduce neural tube defects. The new research suggests both parents' nutritional health during the months surrounding conception may matter.

For couples hoping to conceive, the takeaway is not to begin taking high higher dose supplements on their own. Rather, the study reinforces a broader message: prenatal and preconception health is not solely a woman's responsibility.

As researchers continue investigating the biological contribution of both parents, preparing for pregnancy may increasingly mean looking at the health and nutrition of both parents, not one.

The study is published in Annals of Internal Medicine.