I have a history of preterm birth of twins (31w gestation). assuming my next pregnancy is a singleton, should i do 17p injections to reduce the risk of ptb? are there risks to 17p injections?

Yes: You are a candidate for Progesterone injections, even in the setting of a singleton pregnancy. There are little to no risks of this medication during pregnancy, which is usually started at about 16 weeks.

See your doctor: I think you should really discuss this with your obstetrician. Without other info and without actually seeing a patient, these kind of questions are hard to answer.