Research published in The Lancet says that taking vitamin D supplements in pregnancy seems to make no difference to a child's bone health, in contrast to guidelines in some countries.
University of Bristol investigators in western England looked at vitamin D levels throughout the pregnancy of nearly 4,000 British women.
They then measured the bone mineral content of the women's children at the age of nine.
Vitamin D plays a big role in healthy bones and teeth as it regulates calcium and phosphate in the body.
Eggs, oily fish and meat are all rich in the vitamin, which is also derived from the action of sunlight on skin.
Its importance is such that doctors in some countries recommend pregnant women take a daily supplement to help their baby get stronger bones.
But the guidelines vary and some health watchdogs do not give any advice at all, reflecting conflicting opinions that supplements are effective or -- if used in higher doses -- safe.
The authors say this is the widest and most thorough research into whether maternal vitamin D makes a difference to a child's bone health.
"We believe that there is no strong evidence that pregnant women should receive vitamin D supplementation to prevent low BMC [bone mineral content] in their offspring, although we cannot comment on other possible effects of vitamin D in pregnant women," said researcher Debbie Lawlor.
The World Health Organisation (WHO) on its website says that vitamin D supplements are "currently... not recommended" in order to prevent pre-eclampsia, a highly dangerous condition in pregnancy.