Pregnant women who fasted during the Islamic holy month of Ramazan were no more likely to give birth prematurely than women who didn't observe the fast, but the babies of women who fasted were smaller on average, a Lebanese study has found.

The researchers, whose findings appeared in BJOG: An International Journal of Obstetrics and Gynaecology, found no significant differences in the rate of births before the 37th week of pregnancy among 201 pregnant Beirut women who fasted during the daytime, compared with 201 women who didn't.

“Although results are reassuring as far as there is no increased risk of pre-term delivery, the fact that the mean birth weight was significantly lower in Ramazan-fasted women is alarming,” said study leader Anwar Nassar, a professor of obstetrics and gynecology at the American University of Beirut Medical Center.

During Ramazan, the ninth lunar month of the Islamic calendar, Muslims abstain from eating and drinking during the day. While fasting is compulsory, pregnancy may be “a relative exemption if reasons for maternal/fetal hardship are suspected.”

Nevertheless, many pregnant women ask whether it's all right to fast during Ramazan, Nassar told Reuters Health.

Other studies have looked at fasting during pregnancy, such as in cases of famine or in experiments with calorie restriction, but this is the first in the English literature to look at the effects of Ramazan fasting on pre-term delivery.

For the study, Nassar and his colleagues recruited pregnant women from four medical centers around Beirut in August 2008, matching the characteristics of those who planned on fasting with a comparison group who did not fast.

All the women were in their third trimester during the study period. In 2008, Ramazan took place during September.

Overall, 21 women in each group gave birth before their 37th week of pregnancy, which is considered “pre-term.”

Three fasting women gave birth before their 37th week of pregnancy, compared with one in the non-fasting group, but the researchers say that difference could have been due to chance.

On average, fasting women's babies weighed about 3 kg (around 6.8 lb), compared with the babies of non-fasting women, who averaged 3.2 kg (7 lb).

One possible explanation for the difference is that fasting mothers tended to gain less weight during the Ramazan period, 1.6 kg versus 2.3 kg among non-fasting women.

While the researchers cannot say what a low birth weight could mean for babies later on in life, Nassar noted that it has been linked to heart disease. Other effects of fasting during pregnancy may not be immediate and there could be other consequences as the child grows.

More study is needed, Nassar said. The fasting period in Ramazan can vary considerably, from 10 to 19 hours depending on what time of year the fasting month falls, and in what part of the globe a woman is in.

Moreover, different cultures have different traditions regarding feasting at night to break the fast, so it's hard to generalize about the calorie and nutrition intake of all fasting women during Ramazan.