Vanishing twin syndrome

By trimester

Weeks 1–13

1st trimester

The usual pattern is an early scan showing twins followed by a scan showing one continuing pregnancy. Some people have light bleeding or cramps and others have no symptoms. Ultrasound timing and findings establish what changed; symptoms alone cannot identify a vanishing twin.

Weeks 14–27

2nd trimester

If the loss occurred later, or the twins shared a placenta, the surviving fetus may need more focused growth and anatomy follow-up. The obstetric team should also interpret NIPT and serum screening with the vanished twin in view because placental material can remain detectable.

Weeks 28–birth

3rd trimester

An uncomplicated early first-trimester loss often has a favorable outlook for the continuing singleton. Later loss and monochorionic pregnancy carry different risks, so the delivery and surveillance plan should follow chorionicity, gestational timing, growth, and other ultrasound findings.

What does the evidence show for vanishing twin syndrome?

• A current StatPearls review defines vanishing twin syndrome by early ultrasound evidence of a multiple pregnancy followed by later disappearance of one conceptus. Many patients have no symptoms; bleeding or cramps can occur, and ultrasound follow-up distinguishes the condition from other early-pregnancy causes. 1
• A 2022 review reports that the outlook for the surviving fetus depends on when the loss occurs and placental arrangement. Evidence across studies is inconsistent, with some reporting preterm birth or small-for-gestational-age associations and others not finding the same differences. 2
• A meta-analysis limited to assisted-reproduction pregnancies found no significant difference in overall preterm birth but did find a higher estimate for extreme preterm birth and lower mean birth weight after a vanishing twin. Only five observational studies were included and sensitivity analyses were unstable, so causation and precise risk cannot be inferred. 3
• In a retrospective cohort of 847 vanishing-twin pregnancies undergoing cell-free DNA screening, positive predictive value varied by chromosome and false-positive results occurred. The study compared screening with follow-up outcomes but could not show that time since demise reliably eliminates interference. 4
• A review of biological causes of false-positive cell-free DNA results includes a demised co-twin as a recognized source of discordance. A high-risk NIPT result after a vanishing twin therefore needs individualized genetics review and confirmatory testing rather than being read as a fetal certainty. 5

When should I call my provider about vanishing twin syndrome?

Seek urgent assessment for heavy bleeding, severe or one-sided pelvic or abdominal pain, shoulder pain, fainting, marked dizziness, fever, or fluid leakage. These findings can reflect ectopic or heterotopic pregnancy, substantial blood loss, infection, membrane rupture, or another complication and should not be attributed automatically to a vanishing twin. 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.