Vasa previa

By trimester

Weeks 1–13

1st trimester

First trimester: vasa previa is rarely finalized this early, but placental position, cord insertion, assisted conception, twins, or a bilobed or accessory placental lobe can identify a pregnancy needing targeted follow-up. Early risk factors do not prove that fetal vessels cross the cervix.

Weeks 14–27

2nd trimester

Second trimester: targeted transvaginal ultrasound with color Doppler can map fetal vessels near the cervix. Ask whether the finding is definite, how distance was measured, whether placenta or cord abnormalities coexist, and when reassessment will occur because some early findings resolve as the uterus grows.

Weeks 28–birth

3rd trimester

Third trimester: persistent vasa previa requires an individualized plan for surveillance, possible hospitalization, corticosteroid timing, and cesarean before labor or membrane rupture. Vaginal bleeding, fluid leakage, contractions, or reduced fetal movement needs immediate hospital assessment rather than waiting for the next scan.

What does the evidence show for vasa previa?

• ACOG explains that vasa previa involves fetal vessels crossing the cervical opening and that prenatal identification improves outcomes when management includes cesarean before labor. It describes individualized outpatient versus inpatient surveillance and a broad 34-week to 37-week delivery window. 1
• A meta-analysis of 21 studies included 683 prenatally identified cases and estimated 98.6% perinatal survival. In seven comparative studies, survival was 98.6% with prenatal identification versus 72.1% without it. Observational selection and differences between centers limit causal and individual prediction. 2
• A five-center U.S. retrospective cohort followed 136 antenatally identified cases; 19, or 14%, resolved at a median of 27 weeks. Persistent cases had cesarean at a median of 34 weeks. Center practices and a selected referral population limit a universal schedule. 3
• A systematic review reports that most cases have at least one recognized risk factor, including assisted conception, multiple gestation, velamentous cord insertion, low-lying placenta, or bilobed or accessory-lobed placenta. It also found no clear consensus on hospitalization, cervical-length surveillance, or corticosteroid timing. 4
• In a retrospective multicenter series of 165 prenatally identified pregnancies, 26.1% resolved on later ultrasound. Among 122 persistent cases, 37.7% required unscheduled delivery, 70% of infants entered intensive care, and one neonatal death was attributed to prematurity, illustrating the tradeoff between emergency risk and early birth. 5

When should I call my provider about vasa previa?

Known or suspected vasa previa plus any vaginal bleeding, leaking fluid, regular contractions, sudden pelvic pressure, or reduced fetal movement needs immediate labor-unit assessment. Call emergency services for heavy bleeding, faintness, or signs of imminent birth. Do not wait to see whether bleeding stops after the membranes may have ruptured, because fetal blood loss can progress rapidly. None of these lists replace your own judgment: if this symptom worries you, that on its own is enough reason to check in with your healthcare provider.