How do surgeons perform operations on fetuses without permanently damaging the amniotic sac ?

They same way they avoid permanent damage to pregnant woman’s abdomen (or indeed any surgery). They carefully stitch it all back together at the end.

@Lightlyseared I’m not sure? I thought that the water would break? Like a popped balloon?

Upon completion of the fetal surgery, the fetus is put back inside the uterus and the uterus and abdominal wall are closed up. Before the last stitch is made in the uterine wall, the amniotic fluid is replaced.

Source: https://en.m.wikipedia.org/wiki/Fetal_surgery#Technique

@JLeslie I don’t get it, but thanks. I will let it go. Ok I read more of the details. Makes sense now. Thanks . The sac is refilled. That sounds like an amazing process.

It is incredible that it can be done.