A new study co-authored by the University of Kentucky's Dr. John O'Brien found that applying vaginal progesterone to women who are at a high risk of preterm birth significantly decreased the odds of a premature delivery.

The new study, published in the American Journal of Obstetrics and Gynecology, described a two-prong strategy used by doctors: participating pregnant women underwent a measurement of the cervical length via transvaginal cervical ultrasound to define risk for preterm birth; and those found to have a short cervix were successfully treated with vaginal progesterone. A short cervix defined as a length of 25 millimeters or less is a major risk factor for preterm birth.

Approximately 12.9 million births worldwide are preterm which is defined as less than 37 weeks of gestation. The United States has the highest rate of preterm births in the world. "Early" preterm births -- those less than 32 weeks -- are associated with a high rate of neonatal complications and long-term neurologic disability. "Late" preterm births (between 34 and 36-6/7 weeks) represent 70 percent of all preterm births; and although they have a lower rate of complications than early preterm births, they are still a major health care problem.

The study showed that the vaginal application of progesterone gel significantly reduces the rate of preterm birth in women at less than 33 weeks of gestation, but also is effective at less than 28, 32 and 35 weeks. This means that vaginal progesterone reduces both "early" and "late" preterm births.

Vaginal progesterone administered to women with a short cervix detected via ultrasound also reduced the rate of admissions to the newborn intensive care unit; respiratory distress syndrome; the need for mechanical ventilation; and a composite score of complications that included intracranial hemorrhage, bowel problems, respiratory difficulties, infection and death.

O'Brien, division chief of Maternal-Fetal Medicine at UK, says the progesterone treatment is safe because the natural pregnancy hormone is the made by the placenta and the ovaries during pregnancy.

"For too long, little progress has been made in the prevention of premature births," said O'Brien. "However, this new large study shows that it's possible to both help women determine if they are at risk for preterm birth, and provide a safe and effective treatment to help prevent preterm births."