Do Pregnant Women Have to Fast?
Question

My wife is 7 months pregnant, does she have to fast? If not, what should she do instead of fasting?
Praise be to Allah.Do pregnant women have to fast?
The most correct view compares pregnant and nursing women to those who are sick. So it is permissible for pregnant women not to fast , and all they have to do is to make up for the days they missed , whether they feared for themselves or their child. 
The Prophet (peace and blessings of Allah be upon him) said: “Allah has relieved the traveller of the obligation of fasting and half of the prayer, and He has relieved the pregnant woman and nursing mother of the obligation of fasting.” (Narrated by al-Tirmidhi, 715; Ibn Majah, 1667; classed as sahih by al-Albani in Sahih al-Tirmidhi, 575) (For more, please see Seventy Issues related to Fasting. 
Fasting during pregnancy 
If a pregnant woman fears that fasting may harm her or her baby, then she should follow the ruling on one who is sick. So she may break her fast and she has to make up the days that she did not fast, because Allah says (interpretation of the meaning): 
“and whoever is ill or on a journey, the same number [of days which one did not observe Sawm (fasts) must be made up] from other days.” [al-Baqarah 2:185]
But if she does not fear that she or her baby may be harmed by fasting, then she has to fast, because Allah says (interpretation of the meaning): 
“So whoever of you sights (the crescent on the first night of) the month (of Ramadan i.e. is present at his home), he must observe Sawm (fasts) that month.” [al-Baqarah 2:185]
In most cases, fasting is difficult for pregnant women, especially in the final months, and fasting may affect the pregnancy. So she should refer to a trustworthy doctor for advice. (Al-Sharh al-Mumti’, 6/359) 
And Allah knows best.