Betnesol is indicated if you are at high risk for preterm delivery or have threatened preterm labor. Yes, the injections can cause slight elevation of your blood sugar levels. There is now a rethink on giving these injections weekly. If indicated at 28 weeks, I administer the injections (as mentioned in 2 doses), and again around 34 weeks if not delivered by then. If your cervix is long and os is closed, and you do not have any pain, I do not know why the injections are advised. You should ask your doc- she knows details which you may not know/ are not aware of. Remember, twin pregnancies are high risk pregnancies, and they are at increased risk of preterm delivery.
It is best to follow your doctor's advice. Check with her. Also, trust in your doctor is extremely important. If you don't trust her- change your doctor- you will at least be mentally at peace.