Management of Second Pregnancy After Prior Second-Trimester Abortion
Serial ultrasound to assess cervical length and dilation (Option D) is the recommended initial approach, with subsequent management decisions based on cervical length findings.
Initial Management Strategy
Begin 17-alpha-hydroxyprogesterone caproate (17P) 250 mg intramuscularly weekly starting at 16-20 weeks of gestation and continuing until 36 weeks. This is the first-line therapy for women with a history of spontaneous preterm birth, including second-trimester abortion 1, 2. The Society for Maternal-Fetal Medicine has consistently recommended this approach for singleton gestations with prior spontaneous preterm birth between 20 and 36 6/7 weeks 1.
Cervical Length Surveillance Protocol
Perform serial transvaginal ultrasound cervical length assessments every 2-4 weeks from 16-24 weeks of gestation 2. This surveillance strategy allows for risk stratification and guides subsequent interventions 1.
Decision Algorithm Based on Cervical Length Findings:
If cervical length remains >25 mm: Continue 17P therapy alone and routine obstetric care 1
If cervical length shortens to ≤25 mm before 24 weeks: Offer cervical cerclage placement while continuing 17P therapy 1, 2. Evidence suggests cerclage is more efficacious when cervical length is ≤15 mm, while progesterone appears most effective for moderately short cervical lengths 1
If cervical length is ≤20 mm: Strongly consider cerclage placement, as this threshold represents significant cervical insufficiency 1
Why Not Prophylactic Cerclage at 13 or 18 Weeks?
Prophylactic cerclage placement at a predetermined gestational age (Options A and B) is not recommended without documented cervical shortening. Approximately 69% of women with prior spontaneous preterm birth maintain a cervical length >25 mm throughout pregnancy 1. Placing cerclage in all patients would expose the majority to unnecessary procedural risks when they would not benefit from the intervention 1.
Why Not Clinical Assessment Alone?
Clinical assessment of cervical dilation (Option C) is insufficient as a standalone strategy because:
- Digital cervical examination is less sensitive than transvaginal ultrasound for detecting early cervical changes 1
- By the time cervical dilation is clinically apparent, the optimal window for cerclage placement may have passed 1
- Ultrasound-indicated cerclage (based on cervical length) has demonstrated efficacy in preventing preterm birth when cervical shortening is detected early 1
Critical Pitfalls to Avoid
Do not substitute vaginal progesterone for 17P in this patient population. Multiple randomized controlled trials, including the large OPPTIMUM study (n=1228), have failed to demonstrate efficacy of vaginal progesterone in reducing recurrent preterm birth in women with prior spontaneous preterm birth 1. Vaginal progesterone is reserved for women with sonographically short cervix (≤20 mm) who do NOT have a history of prior spontaneous preterm birth 1.
If cervical shortening develops despite 17P therapy, continue 17P rather than switching to vaginal progesterone. There is no evidence that changing progestogen formulations provides additional benefit, and 17P should be maintained throughout pregnancy 1.
Do not recommend bed rest or activity restriction, as these interventions have no proven benefit and may cause harm 2.
Evidence Strength Considerations
The recommendation for serial cervical length monitoring combined with history-indicated 17P therapy represents a moderate-to-high strength of evidence from multiple Society for Maternal-Fetal Medicine guidelines 1. This approach allows for individualized escalation of care (adding cerclage) only when objective evidence of cervical insufficiency develops, avoiding unnecessary interventions in the majority of patients who will not require them 1, 2.