Fasting during Ramadan does not result in preterm delivery, but could result in a smaller baby.

The average birth weight of babies in the group who fasted was 3 kg. This was less than the average birth weight of babies in the group who had not fasted during this period; the average weight of babies from this group was 3.2 kg. The effects of this decrease in birth weight due to fasting over prolonged periods have not been studied. The weight gain of the mothers during the fasting period was an average of 1.6 kg in those who fasted as compared to 2.3 kg in those who did not fast.
The study is quite small to generalize the results on larger populations. The duration of fasting during Ramadan varies between countries; this factor should be taken into account while applying the results of this study to other populations.
Reference:
1. J Awwad, IM Usta, J Succar, KM Musallam, G Ghazeeri, AH Nassar. The effect of maternal fasting during Ramadan on preterm delivery: a prospective cohort study. BJOG 2012; DOI: 10.1111/j.1471-0528.2012.03438.x.
Source-Medindia