Related to cause. If the cervix dilated very early (the old medical term is 'incompetent' cervix), then the risk is high. If there was an infection, the odds are not very high if the infection was treated completely. If there was a larger than normal uterus due to multiple babies or high amount of fluid, it is unlikely to recur. If the cause is unknown, then refer to answer by dr garvey. Also seek mfm consultation.
Quite high risk. The greatest risk factor for preterm labor and delivery, is a history of preterm delivery. The recurrance of idiopathic preterm delivery is quite high. Women who have experienced preterm delivery should consider treatment with 17 hydroxyprogesterone caproate in subsequent pregnancies for the prevention of preterm labor. This is the only drug currently fda approved for prevention of preterm labor.
30 % The risk of having one spontaneous premature delivery is about 10%. The risk of having a recurrence can be 20-30%. There are several new developments in the area. First the use of Progesterone in women at high risk for premature delivery has shown to decrease their risk. The use of fetal fibronectin has been useful in managing women with premature contractions and has decreased overtreatment.