Cervical Length, Smoking Increase Spontaneous Preterm Delivery Risk

Shortened cervical length in the second trimester and cigarette smoking independently increase the risk for spontaneous preterm delivery, according to Joseph Findley, MD, Charleston Area Medical Center Women and Children’s Hospital, WV. He presented the results of his study in a large cohort of women at the 2011 ACOG meeting.

Cervical length and smoking can identify women at risk for preterm delivery who may otherwise be overlooked, Dr Findley said. “We asked whether we could measure cervical length as a screening test for spontaneous preterm delivery. ACOG does not recommend this, based on the lack of an effective intervention, except for in women with a previous spontaneous preterm delivery. But progesterone gel is now being evaluated, so a treatment could become available,” Dr Findley told the OB/GYN Nurse-NP/PA. “We found that the risk of spontaneous preterm delivery can be seen in patients who were previously thought to have normal cervical lengths.”

Of the 1116 patients studied, 1 was a current smoker. Cervical length was measured by transvaginal ultrasound in the second trimester (15-26 gestational weeks). Mean cervical length was 4.1 cm. “We looked for the optimal cutoff point—that is, the length that maximized the sensitivity and specificity of screening, and we determined the valid cut-off value for short cervical length to be ≤3.71 cm,” he said.

Of the women with a short cervix, 6.7% had a spontaneous preterm delivery compared with <1% among those with cervix >3.71 cm. The short cervix group had a 5-fold increased risk for preterm delivery compared with wo - men with a normal-length cervix.

Women with a cervical length ≤3.0 cm had a 17-fold increased risk. In addition, heavy smoking (>10 cigarettes daily) was an independent risk factor for preterm delivery, associated with a doubling in risk compared with nonsmokers.

“Smoking is not only an independent risk factor for spontaneous preterm delivery, regardless of cervical length, it also has an additive effect in the patient with shortened cervix,” said Dr Findley.