You can always break a lease, but there are legal and financial consequences for so doing.
And this isn't HS where a doctor's note is a free pass. You will still be BREAKING your lease and responsible for the consequences. READ your agreement.
You need to carefully check out safety of premises PRIOR to signing a lease. LL is right, it is what it is, and you accepted it by signing a lease. It's NOT the LL's fault that you're pregnant and that you have decided you don't want to haul a baby up and down the stairs or are belatedly concerned about the safety. And just because a tenant WANTS something fixed, doesn't mean a LL HAS to fix it.
That said, if it is truly a safety issue, not merely your excuses, put it in writing to LL that you are concerned about safety of the stairs and condition of railing and request that he promptly address the issues.
real estate investor