Yes good question:
Lets compare, Rachel could not concieve that is why she was getting the injections we assume..
Claire already pregnant and healthy 8 months pregnant..

My question is why would they have to inject Claire with something when she is already pregant?

It was an injection I remember so its not like they were trying to get amneatoc(sp sorry) fluid for testing...

__________________
Please don't give up, Des. Because all we really need to survive is one person who truly loves us. And you have her. I will wait for
you. Always. I love you, Pen

DESMOND: I love you, Penny. I've always loved you. I'm so sorry. I love you!
PENNY: I love you too.
DESMOND: I don't know where I am, but--
PENNY: I'll find you, Des--
DESMOND: --I promise--
PENNY: --no matter what--
DESMOND: --I'll come back to you--
PENNY: --I won't give up--
BOTH: I promise. I love you.