What can be done for a 12-week pregnant woman carrying twins, where one fetus is non-viable (no heartbeat) and the other is viable (with heartbeat)?

Management of Twin Pregnancy at 12 Weeks with One Non-Viable Fetus

In a 12-week twin pregnancy where one fetus has no heartbeat and the other is viable, expectant management with close surveillance is the recommended approach, allowing the pregnancy to continue while the non-viable fetus is naturally resorbed or retained as the viable twin develops. 1

Immediate Management Steps

Continue the pregnancy with serial ultrasound monitoring of the surviving twin. The loss of one twin in early pregnancy is a recognized phenomenon that typically does not require intervention, and the remaining fetus can continue to develop normally. 2 This condition is sometimes referred to as "vanishing twin syndrome" when it occurs in the first trimester.

Critical First Step: Determine Chorionicity

Before proceeding, you must establish whether this is a monochorionic (shared placenta) or dichorionic (separate placentas) twin pregnancy, as this fundamentally changes the risk profile and surveillance strategy. 3, 1

• If dichorionic: The risk to the surviving twin is minimal, as each fetus has its own placental circulation. Expectant management with standard prenatal care is appropriate. 3

• If monochorionic: There is potential risk of embolic phenomena from the demised twin to the surviving twin through shared placental vascular connections, though this risk is lower at 12 weeks compared to later gestational ages. 3

Surveillance Protocol

For Dichorionic Twins:

• Perform follow-up ultrasound in 2-3 weeks to confirm continued viability of the surviving twin and assess for any complications. 3
• Continue routine prenatal care with ultrasound surveillance every 3-4 weeks if no complications develop. 3
• The demised fetus will typically be resorbed or compressed (fetus papyraceus) and delivered at term with the viable twin. 2

For Monochorionic Twins:

• Perform ultrasound with Doppler studies within 1 week to assess the surviving twin for signs of acute twin-twin transfusion or embolic complications. 3
• Monitor for signs of neurologic injury in the surviving twin, though the risk is lower at this early gestational age compared to later demise. 3
• Increase surveillance frequency to every 2 weeks initially, then adjust based on findings. 3
• Consider referral to maternal-fetal medicine for specialized monitoring. 1

What to Monitor in the Surviving Twin

Assess for these specific complications at each ultrasound:

• Fetal growth parameters: Crown-rump length initially, then standard biometry to detect growth restriction. 3
• Amniotic fluid volume: Oligohydramnios or polyhydramnios may indicate complications. 3
• Fetal anatomy: Complete anatomic survey at 18-22 weeks, as twin pregnancies have higher rates of congenital anomalies (1 in 25 for dichorionic, 1 in 15 for monochorionic-diamniotic). 3
• Doppler studies (if monochorionic): Umbilical artery and middle cerebral artery to detect vascular compromise. 3
• Cervical length assessment at the time of anatomic survey to stratify preterm delivery risk. 3

Maternal Counseling Points

Reassure the patient that:

• The loss of one twin does not typically cause clinical symptoms, though light vaginal bleeding may occur. 2
• The surviving twin has an excellent prognosis for normal development, particularly in dichorionic pregnancies. 2
• No intervention is required to remove the non-viable fetus; it will be managed naturally by the body. 2

Warn the patient about:

• Slightly increased risk of preterm delivery compared to singleton pregnancy, though lower than ongoing twin pregnancy. 4, 5
• Need for continued close monitoring throughout pregnancy. 3
• In monochorionic twins specifically, small risk of neurologic complications to the surviving twin from vascular connections. 3

Common Pitfalls to Avoid

• Do not attempt surgical intervention to remove the demised fetus, as this risks the viable pregnancy. 2
• Do not delay determining chorionicity, as this is critical for risk stratification and surveillance planning. 1
• Do not assume the pregnancy will proceed as a singleton - continue to monitor for twin-specific complications including preterm labor. 4
• Do not perform invasive testing on the demised twin unless there are specific genetic concerns about the surviving twin, as this increases miscarriage risk. 6

When to Consider Specialist Referral

Refer to maternal-fetal medicine if:

• The pregnancy is monochorionic. 1
• Doppler abnormalities develop in the surviving twin. 3
• Growth restriction or other complications are detected. 3
• The patient desires detailed counseling about risks and prognosis. 3, 6