Pregnant women who fast during Ramadan could be putting the health of their unborn baby at risk, according to a new study.
Fasting during the month is one of the five pillars of Islam, although pregnant women are exempt if it poses a risk to their health.
However, some Muslim women still choose to fast, despite the health implications.
Aanisa Butt, 32, fasted during both of her pregnancies.
"I wouldn't fast every day, I would do one day of fasting followed by a day of rest. Doing alternate days helped me keep my energy levels up," she said.
Ramadan is the ninth month of the Islamic calendar and a time when Muslims across the world fast from dawn until sunset.
"When Ramadan falls in the summer, it can be really difficult to stay without food and water the whole day and if you're pregnant it is even more hard," said Aanisa.
"But I wasn't worried about my health or my baby's. I think Allah gives you strength and he protects your unborn child."
Although Aanisa gave birth to two healthy sons, if women fast for long hours during their pregnancy it can result in problems for their unborn child.
A study by scientists in the United States, based on census data from the US, Iraq and Uganda, found that pregnant women who fast are likely to have smaller babies who are more prone to learning disabilities in adulthood.
The researchers from Columbia University found that this trend was most marked if mothers-to-be fasted early on in their pregnancy and during the summer when longer days meant they went more hours without food.
Religious leaders say pregnant women shouldn't attempt to fast as it puts the health of their unborn baby at risk.
Imam Madani Abdur Rahman, from London, says Islam does give pregnant women options.
"We have to assess the situation, if the doctor says fasting could cause problems for the mother or her baby, then women should not fast. Health must always come first," he added.
Pregnant women who request an exemption from fasting are expected to make up the days they have missed after the baby is born.
Nuala Close is a nurse at Barts and London Hospital. She says many women do not make use of this provision.
"If women are exempt from fasting they have to make it up at another time, like once they've finished breastfeeding or in the lighter hours.
"But what we are actually finding is that pregnant patients don't actually like to do this and so often they will try to fast during Ramadan as normal."
For Aanisa, having to make up the days later was one of the main reasons she chose to fast in her pregnancy.
"I find it really difficult to make up the time afterwards especially because no one else in the family is fasting. So I try to do as many as I can during the month," she said.
Scholars say if pregnant women cannot fast after Ramadan for any reason, then they can give money to charity instead.
However, since fasting during the month is seen as an integral part of Muslim culture, many women may feel guilty if they do not observe Ramadan.
Health professionals warn that pregnant women should seek advice if they decide to fast.
"Where Ramadan now falls in August, that is a long time of daylight hours where people will be fasting, that will have a detrimental effect on pregnant women, said Ms Close.
"Pregnant women should discus this with their midwife because it can be very dangerous, not just for the women but also for the unborn child."