Shape of Cervical Funnel Tied to Length of Gestation


Major Finding: High-risk women with a U-shaped cervical funnel gave birth significantly earlier at 31.8 weeks' gestation, versus 34.6 weeks for women with a V-shaped funnel and 34.7 weeks for those with no funnel.

Data Source: Secondary analysis of 301 women in the Vaginal Ultrasound Cerclage Trial.

Disclosures: The study was funded by the National Institute of Child Health and Human Development. Dr. Mancuso disclosed no conflicts of interest.

CHICAGO — The presence of a U-shaped cervical funnel was significantly associated with earlier birth in high-risk women in a planned secondary analysis of the Vaginal Ultrasound Cerclage Trial.

Women with a U-shaped funnel gave birth nearly 3 weeks earlier at a gestational age of 31.8 weeks, compared with 34.6 weeks for women with a V-shaped funnel and 34.7 weeks for those with no funnel, Dr. Melissa Mancuso reported at the annual meeting of the Society for Maternal-Fetal Medicine.

The relationship was independent of cervical length in the women, all of whom had a prior spontaneous preterm birth and a shortened midtrimester cervical length of less than 25 mm.

Women with a U-shaped funnel also were found to have the greatest benefit from cerclage. During a discussion of the study, one attendee asked if the findings suggest that the benefit of cerclage is only in women with a U-shaped funnel.

“What we know from the parent randomized trial is that there is a benefit from cerclage and that benefit increases as your cervical length decreases,” she said. “If there is a U funnel present, that benefit is increased further.”

It's been nearly 2 decades since researchers first described dilation and effacement in normal, term pregnancies as a progression of the funnel- or T-shaped internal cervical os to a Y shape, then a V shape, and finally a U shape (J. Ultrasound Med. 1995;14:719-24). While funneling has been found to be a risk factor for preterm birth in some reports, controversy lingers over its clinical utility and whether the clinical implications of a U- and V-shaped funnel are the same.

Dr. Mancuso reported on 301 women who were randomized to cerclage or no cerclage and underwent serial vaginal ultrasound between 16 and nearly 23 weeks, revealing no funnel in 154 women, a V-shaped funnel in 99, and a U-shaped funnel in 48. At baseline, women with a U funnel had a significantly shorter mean cervical length of 13 mm, compared with 19 mm for women with a V funnel and 21 mm for those with no funnel, said Dr. Mancuso of the University of Alabama at Birmingham. Twice as many women with a U funnel were treated with cerclage vs. no cerclage (32 vs. 16), which was a significant difference.

In a univariate analysis, the presence of a U funnel, but not a V funnel, was significantly associated with an increased risk of preterm birth at all four time points measured. Preterm birth rates in the U-funnel, V-funnel, and no-funnel groups were 23% vs. 6% vs. 8.4% at less than 24 weeks, 38% vs. 17% vs. 12% at less than 28 weeks, 60% vs. 34% vs. 32% at less than 35 weeks, and 73% vs. 50% vs. 47% at less than 37 weeks. There was no significant difference between the no-funnel and V-funnel groups.

After investigators controlled for baseline cervical length and cerclage, a U-shaped funnel remained significantly associated with preterm birth, with adjusted odds ratios ranging from 2.4 to 2.1, Dr. Mancuso said.

Because U-funnel outcomes appeared to be appreciably worse, the researchers investigated the possibility of an interaction between the U funnel and cerclage. Indeed, women with a U-shaped funnel gave birth a mean 4.9 weeks later in gestation with a cerclage than without a cerclage. This relationship remained significant, even after cervical length was controlled for, she said.

Session moderator Dr. Joshua Copel of Yale University in New Haven, Conn., described the findings as interesting and provocative.

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