17 week check up

Friday is almost here. I have my "16 week" really 17 week check up. This is the appointment I have been dreading for the past 4 weeks. I have done tons of research, pondering, and asking friends on this subject that will be discussed at my check up on Friday. It has been recommended to me to get progesterone shots throughout the pregnancy. They are wanting to prevent me from going on bed rest and to keep the baby in as long as possible. It's one of those decisions I feel that I am going to wonder if I did the right thing the entire pregnancy. If I don't get it and go into labor early with a premature baby am I going to kick myself for not doing all I could do to prevent it? If I get future side effects from getting these extra hormones injected into my body, am I going to regret even doing the shots "just in case"? I know what my answer will be on Friday but its still hard not to stress about the "what ifs".