herniated disk- effect of cortisone shots

Hi,
I have been diagonised with Herniated disc in my L5-S1 portion of my lower back.
I happen to have back pain with sciatic nerve on my right leg for more than 6 weeks now,
When am in gabapentin, i sleep better but not for too long.
My neurologist had recommended for cotisone shots earlier, but i thought of waiting.
Now i feel like i should go for cortisone shots.

My question here is I have a possibility of becoming pregnant in couple of weeks.
(i may be already pregnant by few days), Does injecting a cortisone shot affect my pregnancy
or otherwise the fetus?
Is it safe to get the shots during the first trimister of pregnancy.

pls. help, we would want to have this baby to make our family complete.
What do you suggest to manage pain during weight gain.

Thanks in advance.