Majority of scholars recommend pregnant women and nursing mothers to break their fast if her health or the health of the baby requires an immediate attention.

It is an obligation for them to expiate the days of fasting which they have missed after Ramadan has passed and they have safely given birth and assessed as fit to fulfil the expiation.

It is also worth noting that there are discussions among jurists on the obligatory of expiating the missed days or paying fidyah or both for a pregnant and a nursing mother.

If the nursing mother is concerned for the health of their babies, they may opt to a view by Ibn Umar, Ibn Abbas & Sa'id Bin Jubayr, that they are required to only pay fidyah without expiation.

One can hold on to this opinion (i.e. to only pay fidyah) in the event that they have to miss several years of fasting due to pregnancy and breastfeeding and don't have the ability to expiate the missed days.