Preterm Birth in the United States (U.S.) is classified as delivering before 37 weeks, unfortunately all our research efforts have done little to decrease the percentage of preterm birth as well as the other complications of pregnancy that lead to neonatal (during 1st month of birth) death. Medications such as Magnesium Sulfate have not been shown to prolong pregnancy although OB physicians continue to administer it routinely, the same goes for bed rest.
Certain interventions have shown to help babies born early such as corticosteroids (given over a 24-hour period, i.e. Betamethasone and Dexamethasone) to mom between 28-34 weeks. Antibiotics (i.e. Penicillin or Clindamycin) during the labor of anyone less than 37 weeks or who have documented Group B Strep bacteria (by vaginal or urine culture) have decreased the complications associated with preterm delivery.
In the news recently, there have been talks about the use of a certain progesterone hormone, 17-Hydroxyprogesterone, a weekly injection starting between 16-20 weeks and ending at 36 weeks. It is indicated for anyone who has had a previous preterm delivery. This has been known for years but not always implemented by physicians.
The recent news is because a particular drug company is trying to take this medication and change it from generic pricing at $100 per month to over $1500 per month for a branded version, renamed Makena. Luckily, there has been a huge backlash and this is not likely to occur despite initial FDA approval.
More promising is Prochieve, a progesterone vaginal gel already available in the U.S. for infertility which would prevent women from getting painful injections for 20 weeks of their pregnancy(http://www.washingtonpost.com/national/progesterone-gel-lowers-the-risk-of-preterm-delivery-in-pregnant-women-with-a-short-cervix/2011/04/06/AFl7YmuC_story.html).
Be sure to ask your Ob Gyn doctor at your first appointment if Progesterone supplementation can help you if you have had a preterm birth between 20 and 36 weeks.