Is it true that a placenta previa (placenta previa) diagnosed by transvaginal ultrasound (US) at 22 weeks gestation may resolve prior to term?

Placenta Previa Management and Resolution

A placenta previa diagnosed by transvaginal ultrasound at 22 weeks gestation may indeed resolve prior to term. This is the most accurate statement among the options presented regarding placenta previa management.

Resolution of Placenta Previa During Pregnancy

Placenta previa diagnosed in the second trimester frequently resolves before delivery due to the differential growth of the lower uterine segment (known as "placental migration"). According to evidence:

• When diagnosed at 18-20 weeks, if the placenta is more than 2 cm from the internal cervical os, follow-up evaluation is not necessary as it's unlikely to develop into placenta previa at term 1
• Approximately 6.2% of patients have placenta previa in the first trimester, but only a small percentage persist until term 2
• The incidence of placenta previa diagnosed by transvaginal ultrasound at 15-20 weeks is about 1.1%, with only 14% persisting until delivery 3
• The later in gestation that placenta previa is diagnosed, the more likely it will remain a placenta previa 1

Assessment of Other Statements

Regarding restricted maternal activity:

While pelvic rest (avoiding sexual intercourse) is recommended for patients with placenta previa, there is insufficient evidence in the guidelines to support that restricted maternal activity reduces the chance of antepartum bleeding. The guidelines focus on imaging evaluation and delivery planning rather than activity restriction as a preventive measure.

Regarding timing of cesarean section:

For stable patients with placenta previa, delivery is typically planned at 34-35 weeks, not after 39 weeks 4. Earlier delivery may be required if bleeding becomes heavy, maternal condition deteriorates, or fetal compromise develops.

Regarding placental edge proximity to internal os:

The statement that cesarean section must be performed if the placental edge is within 20mm of the internal os is not supported by the guidelines. The decision for cesarean delivery depends on multiple factors including the degree of previa, bleeding episodes, and gestational age.

Imaging Evaluation Protocol

1. Initial assessment: Transabdominal ultrasound followed by transvaginal ultrasound is the recommended approach 1, 4
2. Transvaginal ultrasound: Essential for accurate assessment of placental location relative to the internal cervical os 1
3. Doppler evaluation: Should be considered if abnormalities of placental tissue or placental-myometrial interface are detected 1

Risk Factors and Complications

Even with resolved placenta previa:

• Women remain at 2.5 times higher risk of postpartum hemorrhage compared to those who never had previa 5
• Higher rates of antepartum hemorrhage, abdominal delivery, and abnormally adherent placenta are associated with thick-edge placenta previa 6

Predictive Factors for Persistence

The likelihood of placenta previa persisting until term increases with:

• Placenta covering the internal cervical os by ≥1.6 cm in the first trimester 2
• Placenta overlapping the internal os by ≥10 mm between 15-24 weeks (100% sensitivity, 85% specificity) 3
• Placenta extending ≥25 mm over the internal os at 18-23 weeks (40% positive predictive value, 80% sensitivity) 7

Proper evaluation with transvaginal ultrasound is critical for accurate diagnosis and management planning, with follow-up ultrasounds recommended when the placental edge is in close proximity to or overlapping the internal cervical os.