How is preterm labor risk assessed in pregnant women with a history of midtrimester loss?

Updated: May 04, 2021
  • Author: Michael G Ross, MD, MPH; Chief Editor: Carl V Smith, MD  more...
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A history of prior midtrimester losses is carefully reviewed at the initial visit to distinguish incompetent cervix from other causes (eg, abruption, infection, intrauterine death, ruptured membranes) with review of the pathology or autopsy reports if available. Parental karyotypes are generally not helpful unless more than one midtrimester loss has occurred or a midtrimester loss has occurred in which the fetus was structurally or genetically abnormal.

Specific laboratory tests, including a rapid plasma reagin test, gonorrheal and chlamydial screening, vaginal pH/wet smear/whiff test, anticardiolipin antibody, lupus anticoagulant antibody, activated partial thromboplastin time, and a 1-hour glucose challenge test are helpful in the evaluation. In addition, one should consider TORCH (toxoplasmosis, other infections, rubella, cytomegalovirus infection, herpes simplex), immunoglobulin G, and immunoglobulin M screening whenever the historical or clinical suspicion is present. However, a random drug screen is not always recommended unless other supporting high-risk behavior exists.

A preconceptual hysterosalpingogram may be of benefit in patients with a history of 2 or more midtrimester losses. One can also attempt to pass a No. 8 Hegar dilator into the nonpregnant cervix; easy passage may be a sign of cervical incompetence. During pregnancy, whenever the suspicion of incompetent cervix exists, one should consider performing baseline transvaginal ultrasonography to assess cervical length, especially at 13-17 weeks’ gestation; abnormal findings include a length less than 2.5 cm, funneling greater than 5 mm, or dynamic changes.

A cerclage may be indicated after 2 or more midtrimester losses consistent with incompetent cervix or in which the etiology is unknown and the transvaginal ultrasonography of the cervix is abnormal. A cerclage is usually performed electively at 13-17 weeks’ gestation.

A genetic amniocentesis may be performed prior to the placement of cerclage in patients at high risk for genetic disease. Prior to an elective cerclage, sampling the patient's vagina and cervix for BV, gonorrheal, chlamydial, or trichomonal infection is also recommended, with appropriate treatment instituted. The efficacy of prophylactic antibiotics for cerclage is yet to be demonstrated.

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