A pregnant woman is permitted to delay making up missed days of fasting if she fears for her fetus
15-6-2014 | IslamWeb
Question:
I am pregnant. I did not fast in Ramadan and I want to make up for the missed fast. However, I could not do so out of fear that fasting might be harmful to my fetus. Please advise!
Answer:
All perfect praise be to Allah, The Lord of the Worlds. I testify that none is worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
Scholars unanimously agree that making up for the missed days of Ramadan is due. Moreover, one can delay it as long as the next Ramadan has not yet started. It was narrated on the authority of ‘Aa’ishah 
that she said: “I would have to make up for missed days of Ramadan and I would not be able to make them up until Sha‘baan.” [Al-Bukhari and Muslim]
It is impermissible to delay making up fasting until the following Ramadan comes without a Sharee'ah-approved excuse. This is because fasting is a recurring worship, so it is impermissible to delay the first until after the coming of the following one. In this regard, it is similar to the obligatory prayers.
If the person delays making up the missed fast until after the next Ramadan comes because of a Sharee'ah-approved excuse, then he is required to make up for the fast only. If there is no Sharee'ah-approved excuse, then one has to make up for the missed fast and feed a needy person for every day that he missed. This is the opinion of the majority of scholars.
Accordingly, you are allowed to delay making up for the missed days until delivery, even if another Ramadan will have entered. You are only required to make up for the missed days. Since pregnancy is a considerable excuse for breaking the fast, then it is worthier to allow delay of making up for it. However, it is conditioned that you most believe that fasting will probably be harmful to you or to your fetus.