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Natural History of Cervical Funneling in Women at High Risk for Spontaneous Preterm Birth

From the ¹Department of Obstetrics and Gynecology, Division of Maternal–Fetal Medicine, Jefferson Medical College of Thomas Jefferson University, Philadelphia, Pennsylvania; ²Department of Obstetrics and Gynecology, University of Alabama at Birmingham, Birmingham, Alabama; ³The Biostatistics Center, George Washington University, Bethesda, Maryland; ⁴Department of Obstetrics and Gynecology, Emory University School of Medicine, Atlanta, Georgia; ⁵Department of Obstetrics and Gynecology, Wake Forest University School of Medicine, Winston-Salem, North Carolina; ⁶Department of Obstetrics and Gynecology, University of Utah, Salt Lake City, Utah; ⁷Department of Obstetrics and Gynecology, University of Cincinnati, Cincinnati, Ohio; ⁸Department of Obstetrics and Gynecology, University of Texas at San Antonio, San Antonio, Texas; and ⁹Department of Obstetrics and Gynecology, University of Tennessee, Memphis, Tennessee, and the National Institute of Child Health and Human Development, Bethesda, Maryland.

OBJECTIVE: To estimate the natural history of funneling in the second trimester by transvaginal ultrasonograms and whether funneling increases the risk of spontaneous birth.

METHODS: Secondary analysis of a blinded, multi-center observational study of women with at least one prior spontaneous preterm birth at 16.0–31.9 weeks who subsequently carried singleton gestations. Cervical length, funneling (membrane prolapse greater than or equal to 5 mm), funnel shape, and dynamic changes were recorded at 16–18 weeks, and then every 2 weeks until 23.9 weeks. Managing obstetricians were blinded to the ultrasonography results. The primary outcome was gestational age at delivery.

RESULTS: Five hundred ninety scans were performed in 183 women, of which 60 (33%) had funneling observed on at least one of the serial evaluations. These 60 women delivered at an earlier gestational age at delivery than the 123 women without funneling (31.7±7.9 weeks compared with 36.9±4.4 weeks; P<.001). In the 60 women with funneling on at least one evaluation, the progression over time of internal os cervical anatomy from a "T" to a "V" to a "U" shape was associated with earlier gestational age at delivery, whereas resolution of "V" shape funnels was associated with term delivery. Women with a shortened cervical length less than 25 mm (n=60) had a similar gestational age at birth with or without funneling (30.6±8.0 weeks compared with 31.9±6.6 weeks; P=.59). After controlling for the shortest observed cervical length, largest funnel percent was not a significant independent risk factor.

CONCLUSION: The natural history of second-trimester funneling has significant variability and a significant association with earlier gestational age at delivery. As an independent finding, funneling does not add appreciably to the risk of early gestational age at delivery associated with a shortened cervical length.

LEVEL OF EVIDENCE: II