Sheikh `Abd Allah Nâsir al-Sulamî, professor at the Higher Juridical Institute
If a pregnant woman or a nursing mother does not fear any harm on herself or her child from fasting, then she is obligated to fast as other normal women. This is the saying of the majority of scholars.
There is disagreement among the scholars about the situation where the woman fears harm for herself or for her child. The opinions in this case are three:
1. The opinion of Ibn `Abbâs (also attributed to Ibn `Umar) is that she has to break her fast and feed a poor person for each day by way of expiation. She does not have to make up the days that she missed.
2. According to the Hanbalî School of Law, if fasting is difficult for her, then she only has to re-fast the missed days. In this way, she is the same as a sick person. However, if she fears harm on her baby and not on herself (or if she fears her breast milk will run dry), then she has to feed a poor person as expiation and make up the fasts that she missed.
3. The opinion of some people of knowledge (and one of the opinions expressed by Ahmad) is that the pregnant woman or nursing mother, if she fears harm on herself or her baby, is obligated to break her fast and make it up later, without having to feed a poor person as expiation.
The third opinion is the preferred opinion that is supported by the evidence. There is an authentic hadîth related by Anas b. Malik al-Ka`bî that the Prophet (peace be upon him) said: “Allah has exempted women from fasting and praying during their menses and exempted them from fasting when pregnant or nursing."
Also, the Prophet (peace be upon him) never asked women to feed the poor or do anything else as expiation. His not mentioning more detail means that there is nothing else expected from them.
And Allah knows best.
Source: Islam Today