Answered by Shaykh Faraz Rabbani
If a couple is trying to conceive, and it is possible the wife has become pregnant during Ramadan – is it permissible for the Sister to abstain from fasting until she finds out for certain about her condition, since the first few weeks of gestation are the most vital in fetal development?
This is not a valid basis not to fast. Allah has not made anything that is in itself harmful obligatory on us in our worship. Fasting is not harmful to the human body, even when pregnant, except in rare cases.
Allah Most High said, “Allah does not make a soul accountable for more than it can bear.”
Besides this, the legal maxim is that, “Mere possibilities are of no consequence.” (la `ibrata bi’l wahm.) [Majalla, Ashbah] That is, legal rulings are not based on mere possibilities that are not backed up by reasonable surety or certainty.
See attached answers.