Mommy, first thing, please trust your OB on this one, okay? Siya ang expert sa case mo, at kung sinabi niya na kailangan, mayroon siyang good reason based sa thin uterus mo.
A few of us moms in our circle went through similar situations, at honestly, the injections your doctor mentioned are standard practice na para sa babies na maagang igisip. Hindi kami nakita ng obvious side effects sa babies namin, normal lang sila lumaki at healthy. But I won't pretend I'm a doctor, kaya please ask your OB directly about what to expect, any risks, or concerns mo. That's really the best source for your peace of mind.
Praying for you at baby mo! You're doing the right thing by being cautious.