Pregnant women can not be separated from two things:
1. Women are strong and spirit to live fast, not difficult for him to live fast and do not take effect for the fetus, it is mandatory for pregnant women to fast. Because when it does not exist udzur him for not fasting.
2. The woman was not able to live weight and body limp when fasting or fasting and the other reason to live, then in this condition he should not fast. Especially if it took effect on the fetus, this condition is also mandatory for him not to fast.
[Fataawa ash-Shaykh Ibn ‘Uthaymeen, 1/487]
Shaykh ‘Abdul’ Aziz bin ‘Abdillah bin Baz rahimahullah said,
Status of pregnant and lactating women is like a sick person. If it is difficult to live fasting, then he should not fast, but still he should mengqodho (nyaur) fasting when he was able to later, his status as a sick person. Some scholars argue enough for pregnant and lactating women to fulfill his fast replacing fidyah, which feed on the poor who are not fasting for the day. But this opinion is a weak opinion. Right, keep him perform qodho fasting as a traveler and the sick. Allah the Exalted says,
ومن كان مريضا أو على سفر فعدة من أيام أخر
“And whoever is ill or on a journey (then he break), then (subject needs to be fast for him), as much as the day he left it, on the other days.” (Surat al-Baqara: 185)
إن الله وضع عن المسافر نصف الصلاة والصوم وعن الحبلى والمرضع
“Verily Allah relieve half the prayer of a traveler, also fasting of pregnant and lactating women.” (Reported by the five)
[Tuhfatul Brotherhood bi bi Arkanil Ajwibah Muhimmah Tata’alluq Islam, p. 171]