Two-vessel umbilical cord

By trimester

Weeks 1–13

1st trimester

A two-vessel cord may be suspected early, but the mid-trimester detailed anatomy ultrasound is central to deciding whether the single umbilical artery is truly isolated. Early screening results do not replace a careful structural survey.

Weeks 14–27

2nd trimester

After the finding, the sonographer and maternal-fetal medicine team review the heart, kidneys, spine, limbs, placenta, cord insertion, growth, and other markers. When no structural finding or growth restriction is present, SMFM does not advise extra aneuploidy evaluation solely because of isolated single umbilical artery.

Weeks 28–birth

3rd trimester

SMFM recommends a third-trimester growth ultrasound and consideration of weekly fetal surveillance from 36 weeks for isolated single umbilical artery. If growth restriction or another complication develops, monitoring and delivery timing follow that condition rather than the cord-vessel count alone.

What does the evidence show for two-vessel umbilical cord?

• SMFM defines an isolated soft marker as one found without a structural anomaly, growth restriction, or another marker after a detailed ultrasound. For isolated single umbilical artery, it recommends no extra aneuploidy evaluation solely for the marker, a third-trimester growth ultrasound, and consideration of weekly surveillance from 36 weeks. 1
• A 2021 systematic review pooled 11 retrospective studies with 1,533 isolated single-artery cases and found associations with small-for-gestational-age birth, preterm birth, pregnancy-related hypertension, intrauterine death, cesarean birth, and NICU admission. High heterogeneity and observational designs limit individual risk prediction and causal claims. 2
• A retrospective cohort compared 219 isolated single umbilical artery pregnancies with 219 three-vessel-cord controls and found more small-for-gestational-age births and pregnancy-related hypertension, but not significantly more spontaneous preterm birth. Retrospective selection and residual confounding limit interpretation. 3
• An earlier meta-analysis of seven studies and 928 isolated cases found no statistically significant increase in small-for-gestational-age birth, perinatal mortality, or aneuploidy and substantial heterogeneity. Its conclusions conflict with later pooled evidence, helping explain why guidance favors surveillance without presenting poor outcome as inevitable. 4
• A review of genitourinary findings notes that kidney and urinary anomalies associated with a two-vessel cord are often visible on routine prenatal ultrasound and may be minor. It did not support automatic extra postnatal urologic screening when prenatal imaging and examination are normal. 5

When should I call my provider about two-vessel umbilical cord?

A two-vessel cord itself does not cause symptoms. Seek same-day maternity guidance for reduced fetal movement or a new concern about growth, and urgent care for vaginal bleeding, fluid leakage, regular preterm contractions, severe headache with vision changes, or severe upper abdominal pain. These signs require assessment based on the whole pregnancy, not attribution to the cord finding. Whatever the pattern, any symptom that feels beyond your usual range is a reason to call: obstetric teams expect these questions and would rather hear early than late.