A mother's vitamin D supply is passed to her baby in utero and helps regulate processes including brain development, the study, published in the Journal of Nutrition, reported.
According to the researchers, vitamin D deficiency is common among the general population as well as pregnant women, but 'Black' women are at greater risk.
"Melanin pigment protects the skin against sun damage, but by blocking UV rays, melanin also reduces vitamin D production in the skin," said study lead author Melissa Melough from the Seattle Children's Research Institute in the US.
"Our work brings greater awareness to this problem, shows the long-lasting implications of prenatal vitamin D for the child and their neurocognitive development," Melough added.
According to the study, as many as 80 per cents of Black pregnant women in the US may be deficient in vitamin D.
Of the women who participated in the study, approximately 46 per cent of the mothers were deficient in vitamin D during their pregnancy, and vitamin D levels were lower among Black women compared to White women.
The researchers recruited pregnant women to join the study starting in 2006 and collected information over time about their children's health and development.
After controlling for several other factors related to IQ, higher vitamin D levels in pregnancy were associated with higher IQ in children ages 4 to 6 years old.
Although observational studies like this one cannot prove causation, the research team believes that the findings have important implications and warrant further research.
"People aren't making up that gap through sun exposure or supplementation, people will probably become deficient," the study author wrote,
Foods that contain higher levels of vitamin D include fatty fish, eggs and fortified sources like cow's milk and breakfast cereals.
Additional research is needed to determine the optimal levels of vitamin D in pregnancy, but Melough hopes this study will help to develop nutritional recommendations for pregnant women.