Dilatation, History Both Predict Preterm Birth


RENO, NEV. — Cervical dilatation at presentation and over the 6 hours following admission was highly predictive of preterm birth in women admitted with preterm labor, but obstetric history also contributed important information about which mothers were likely to deliver before 34 weeks' or 37 weeks' gestation.

Dr. Jamie A. Bastek and associates in the department of obstetrics and gynecology at the University of Pennsylvania, Philadelphia, reviewed the records of 400 women with singleton pregnancies who were admitted in preterm labor before 34 weeks' gestation.

The researchers sought to determine whether the risk of preterm birth could be stratified based on a number of easily identifiable variables, including cervical dilatation and a prior history of preterm or full-term birth.

Dr. Bastek presented their results at the annual meeting of the Society for Gynecologic Investigation.

“As tocolytics are not without harm, we felt it was important to see if we could identify women with a low likelihood of preterm birth who could be managed without admission and/or tocolytic agents” she said in an interview at the meeting, where the study was presented in poster form.

As expected, the total cohort had a significant risk of early delivery.

Nearly 45% delivered before 34 weeks, and 63% delivered before 37 weeks' gestation.

In trying to determine what distinguished the women who delivered after 37 weeks, Dr. Bastek and associates found a number of features conferring protection, including later gestational age at presentation, less cervical dilatation at presentation, smaller rates of change in cervical dilatation, and obstetric history.

Presentation at fewer than 25 weeks' gestation conferred more than a 15-fold increase in the odds of delivering before 34 weeks, compared with women who presented at 32 weeks' gestation. Presentation before 28 weeks was also a noteworthy risk, bestowing 3.5 times the risk of delivering before 34 weeks.

However, presenting at more than 30 weeks' gestation did not demonstrate elevated odds of delivering before 34 weeks or before 37 weeks, compared with presentation at 32 weeks' gestation.

Cervical dilatation—both on presentation and over the course of 6 hours following admission—was significantly predictive of preterm birth, even after controlling for multiple other variables such as maternal age, race, prenatal care, and gestational age on admission.

Each 1-cm increase in cervical dilatation on presentation more than doubled the odds of delivering before 37 weeks, a significant finding (P less than .0001). However, this risk was modified depending on obstetric history.

At a dilatation of 2 cm on admission, for example, the patients who were at highest risk of a preterm birth before 37 weeks were those with no previous births, followed by those with one or more prior preterm deliveries. Rates were lower for mothers who had a history of both preterm and full-term deliveries, and for those who previously had only had full-term deliveries.

The interaction between obstetric history and cervical dilatation was complex.

Patients with a previous preterm birth had the highest baseline risk of another preterm delivery before 37 weeks if cervical dilatation was not taken into consideration.

Within each obstetric history cohort, advancing cervical dilatation was significantly associated with preterm birth before 34 and 37 weeks. Advancing cervical dilatation had the greatest impact on patients with no prior preterm birth and the least impact on those with only a prior preterm birth.

Notably, more than 60% of women with a history of one or more full-term deliveries and no preterm deliveries carried their pregnancies beyond 34 weeks.

What happened after admission was also very relevant to the risk of preterm delivery.

Just 17.8% of the cohort (71 patients) delivered within 6 hours of admission.

Among the remaining 329 women, a 1- to 2-cm change in cervical dilatation after admission conferred almost a threefold risk of delivery before 34 weeks and a twofold risk of delivering before 37 weeks.

A 3-cm or greater change in cervical dilatation was associated with a nearly 12-fold increase in risk of a preterm birth before 34 weeks and a sevenfold increase in the odds of delivering before 37 weeks.

All eight women with more than a 4-cm change in dilatation over the first 6 hours post admission delivered at fewer than 34 weeks.

The research pointed to a number of factors that should be considered in the management of women with preterm labor, especially gestational age at presentation; cervical dilatation on presentation and cervical change over the 6 hours following admission; and obstetric history.

Further research is planned to randomize women with no previous preterm births and a low-risk cervical dilatation profile to tocolysis or expectant management.

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