Fasting During Pregnancy: Obligatory?
Question

Is it better Islamically for a pregnant Muslim woman to fast or not fast in the month of Ramadan?.
Praise be to Allah.Is a pregnant woman obliged to fast?
A pregnant Muslim woman is obliged to fast , just like anyone else, unless she fears for herself or for her baby, in which case it is permissible for her not to fast. 
Ibn 'Abbas (may Allah be pleased with him) said, concerning the verse (interpretation of the meaning):  
“And as for those who can fast with difficulty, (e.g. an old man), they have (a choice either to fast or) to feed a miskeen (poor person) (for every day).” [al-Baqarah 2:184] 
“This was a concession granted to old men and old women who are able to fast but it is difficult, so they are allowed not to fast, and must feed one poor person for each day ; and for those who are sick or pregnant, if they fear for their children, they are allowed not to fast and must feed (one poor person for each day).” (Narrated by Abu Dawud, 2317; classed as sahih by al-Albani in Irwa al-Ghalil, 4/25, 18) 
Cases of fasting during pregnancy
It should be noted that it may be permissible, obligatory or haram for a pregnant woman not to fast. 

It is permissible for her not to fast if fasting is too difficult for her, but will not harm her. 
It is obligatory for her (not to fast) if fasting will cause harm to her or her baby. 
It is haraam for her (not to fast) if no hardship results from her fasting. 

Shaykh Ibn ‘Uthaymin (may Allah have mercy on him) said: 
In the case of a pregnant woman, one of two scenarios must apply: 

She is strong and active, and fasting does not cause any hardship to her or affect her baby. This woman is obliged to fast, because she has no excuse for not fasting. 
When a woman is not able to fast, because the pregnancy is too difficult for her, or because she is physically weak, or for some other reason. In this case she should break the fast, especially if it will cause harm to her baby – in which case she is obliged not to fast. (Fatawa al-Shaykh Ibn ‘Uthaymin, 1/487)

Shaykh Ibn Baz (may Allah have mercy on him) said: 
“Pregnant and breastfeeding women come under the same ruling as those who are sick. If fasting is too difficult for them, it is prescribed for them to break the fast, and they have to make up missed fasts when they are able to do so, just as in the case of one who is sick. 
Some of the scholars were of the view that it is sufficient for them to feed one poor person for each day missed, but this is a weak view. The correct view is that they have to make up the missed days, as is the case of those who were sick and for travelers, because Allah says (interpretation of the meaning): 
“but if any of you is ill or on a journey, the same number (should be made up) from other days.” [al-Baqarah 2:184] 
This is also indicated by the hadith of Anas ibn Malik al-Ka’bi, according to which the Messenger of Allah (peace and blessings of Allah be upon him) said: ‘Allah has exempted the traveler from the obligation of fasting and has reduced the prayer by half for him, and has exempted pregnant and breastfeeding women from the obligation of fasting.” (Narrated by the five) (Tuhfat al-Ikhwan bi Ajwibah Muhimmah Tata’allaq bi Arkan al-Islam, p. 171) 
For more, please see these answers: 128804 and 50762 .              
And Allah knows best.