What is the role of cervical trauma in the etiology of preterm labor?

Updated: May 04, 2021
  • Author: Michael G Ross, MD, MPH; Chief Editor: Carl V Smith, MD  more...
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The most common etiologies for cervical injury are elective abortion, surgeries to treat cervical dysplasia, and injury occurring at delivery. A single uncomplicated elective abortion at less than 10 weeks’ gestation does not increase the risk of midtrimester loss or preterm birth unless the cervix has been forcibly dilated to more than 10 mm at the time of the abortion. However, patients with a history of multiple first-trimester elective terminations or one or more second-trimester elective abortions may be at increased risk for preterm delivery. Cervical dilatation with laminaria or cervical ripening agents, such as misoprostol, appears to be less traumatizing to the cervix than mechanical dilation.

Cervical dysplasia should be treated appropriately whenever diagnosed. However the incidence of preterm birth and cervical incompetence may be increased 200-300% after preconceptual surgical treatment (eg, cold knife cone, cryoconization, laser cone, LEEP) of cervical intraepithelial neoplasia (CIN). The risk of subsequent preterm delivery may be proportional to the amount of cervical tissue removed during surgery. Surprisingly, the ease of performing LEEP for relatively minor abnormalities may have paradoxically led to more cervical injury than was observed with the relatively more invasive cone biopsy.

Obstetric trauma may be underestimated as a risk for midtrimester loss or preterm birth. While women may relate a history of cervical laceration, often they are unaware of the injury and the obstetric records of the previous delivery may be misleading as to the extent of the cervical injury. Therefore, visual inspection of the cervix is important to assess the degree of injury and risk. Defects that involve more than 50% of the cervical length may indicate a higher risk for midtrimester loss. [7] The accuracy of transvaginal ultrasonic measurements to determine risk of cervical incompetence, specifically in the presence of a history of cervical trauma, has yet to be determined.

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