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Winter pregnancies may be harmful for babies' bone growth, a new study from Ireland reports. The researchers found that babies born in the wintertime may suffer from vitamin D deficiency causing them to have less bone growth. The study, published in the journal Fertility and Sterility, reported that women who are pregnant from October through to March tend to get less vitamin D due to the lack of sun when compared to women who are pregnant from April through to September.

The study analyzed the data from 60 Caucasian women and their babies at a Dublin hospital. Roughly half of the women started their pregnancies in September or October and the other half started their pregnancies in March or April.  Each mother's vitamin D levels and their fetuses vitamin levels found from the blood of umbilical cord were measured 12 to 16 weeks into the study and then again at 28 weeks. At 20 and 34 weeks in the pregnancy, the researchers measured the babies' thighbones as well.

The study found that the babies born from winter pregnancies had shorter thighbones and had lower levels of vitamin D.  The winter babies were 47 percent deficient where as the summer babies were 43 percent deficient. The evidence was not present until after a few months into the pregnancy. At the initial start, the summer pregnancy group had a higher percentage of vitamin D deficiency.

Vitamin D is important for maintaining calcium levels and promoting healthy bone growth. Due to this finding, researchers stress that pregnant women living in higher altitudes and get less sunlight should consider taking vitamin D supplements.