Babies born early (before 37 weeks of pregnancy) can have health problems, including breathing and feeding problems, vision problems, and learning problems.
The progesterone shot (sometimes called "17P" for the drug name [17 alpha-hydroxyprogesterone caproate] or its brand name, Makena) can help prevent an early birth. 17P has the hormone in it, which helps prevent contractions. The uterus contracts during labor to help "push" a baby out of the womb for delivery.
Doctors recommend starting 17P shots during the second trimester of pregnancy (usually between 16 and 20 weeks), and continuing them until 36 weeks. Health care providers give the shots in the back of a woman's arm, or in the hip or thigh area.
As with any shot, there's a risk of minor side effects like redness and soreness at the shot site. Rarely, some women get blood clots or have allergic reactions.