Monochorionic twins share one placenta. Vascular connections within that placenta create complications that do not occur in the same way in dichorionic twins. This is why chorionicity should be determined early and why monochorionic pregnancies need a specific ultrasound schedule rather than routine twin follow-up.
Twin-to-twin transfusion syndrome (TTTS) involves an imbalance in blood flow across placental connections, producing characteristic amniotic-fluid and bladder changes. Twin anaemia–polycythaemia sequence (TAPS) is a different imbalance that is assessed primarily through middle cerebral artery Doppler rather than the classic fluid pattern. Selective fetal growth restriction involves unequal placental sharing and requires interpretation of growth, fluid, and Doppler.
What an expert assessment reviews
The scan should establish gestational age, chorionicity and amnionicity, fetal anatomy, placental and cord-insertion findings, growth, deepest vertical pocket in each sac, bladder filling, umbilical artery Doppler, middle cerebral artery Doppler, and ductus venosus findings when indicated.
The label alone does not determine treatment. Severity, gestation, progression, fetal cardiac function, cervical length, membrane status, coexisting abnormalities, and maternal condition all influence the plan.
Possible pathways
Management may include close surveillance, amnioreduction for selected circumstances, fetoscopic laser treatment of placental vascular connections, selective procedures in exceptional situations, planned delivery, or neonatal preparation. Fetoscopic laser is intended to treat the shared placental mechanism in eligible TTTS; it does not erase all risks of monochorionic pregnancy.
Counselling should address procedure-related pregnancy loss, membrane rupture, preterm birth, recurrence or persistence of complications, neurological injury, unequal outcomes between twins, and the need for continued surveillance after treatment.
Planned UAE service
Suspected TTTS or TAPS should be referred immediately because staging and treatment windows are time-sensitive. The dated programme-status panel gives the current TTTS-laser pathway classification; intervention remains subject to specialist confirmation, staging, technical candidacy, governance, and informed consent.
Explore the mechanism
Different problems.
Different targets.
Choose a treatment to see the problem it addresses, what needs checking first, and why follow-up still matters. This is an explanation, not a treatment recommendation.
Fetal anaemia
Fetal transfusion
Severe anaemia means the fetal blood cannot carry enough oxygen. It can strain the heart and, in some cases, contribute to hydrops. A transfusion addresses the shortage of red blood cells.
- The findingFetal anaemia
- The treatment targetOxygen-carrying capacity
- The intended changeReplace red blood cells
Before the decision
The cause of anaemia, middle cerebral artery Doppler, gestational age, fetal wellbeing, and the safest access route.
What treatment cannot promise
Replacing red cells does not necessarily remove the cause. Repeat transfusions and a coordinated birth plan may be needed.
After the procedure
Reassess for recurrent anaemia and plan the next review, further treatment, and newborn care.
Selected TTTS
Placental laser
In TTTS, connected placental vessels contribute to unbalanced circulation between twins. Fetoscopic laser targets these connections; draining amniotic fluid alone does not disconnect them.
- The findingSelected TTTS
- The treatment targetCommunicating placental vessels
- The intended changeInterrupt the abnormal exchange
Before the decision
Chorionicity, the fluid around each twin, bladder findings, Doppler, gestational age, stage, and maternal symptoms.
What treatment cannot promise
Laser cannot guarantee survival or remove every later risk. TTTS and TAPS are distinct conditions and need the correct diagnosis.
After the procedure
Continue specialist ultrasound surveillance of both twins, with attention to recurrent imbalance, anaemia, growth, and neurological assessment.
Selected fluid collections
Drainage & shunts
A large fluid collection can compress organs or interfere with their function. In selected conditions, a shunt provides a route for continued drainage rather than a single aspiration.
- The findingSelected fluid collections
- The treatment targetPressure in a defined space
- The intended changeCreate a drainage route
Before the decision
The exact fluid location, its cause, whether compression is important, associated findings, genetics where indicated, and the expected benefit.
What treatment cannot promise
A shunt may block or move. Drainage may not treat the underlying genetic, cardiac, or other cause of the collection.
After the procedure
Check the collection, organ response, shunt position, and whether the overall pregnancy plan needs to change.
Excess amniotic fluid
Amnioreduction
Amnioreduction removes excess fluid from around the baby in selected situations. Fluid around the baby is different from fluid inside the baby, which may be part of hydrops.
- The findingExcess amniotic fluid
- The treatment targetAmniotic fluid volume
- The intended changeReduce fluid and pressure
Before the decision
The reason for excess fluid, maternal symptoms, cervical and membrane factors, fetal findings, and whether a cause-specific treatment is needed.
What treatment cannot promise
Fluid can build up again. This procedure does not replace placental laser when laser is indicated for TTTS.
After the procedure
Review maternal symptoms, fluid reaccumulation, and the underlying diagnosis to decide on monitoring or further care.
Medical references
SMFM Consult Series #72 — TTTS & TAPSDetailed condition-specific references accompany the linked guides on this site.
The essential distinctions
One placenta changes how twins are monitored.
Twins may share a placenta while having separate amniotic sacs. Placental connections can allow blood to flow between the babies.
- Shared placental vessels
TTTS and TAPS arise from particular patterns of shared circulation. They are different conditions.
- Separate fluid spaces
Fluid around each baby is assessed alongside bladders, growth, and Doppler.
- Two individual assessments
The size of one baby alone cannot diagnose a transfusion syndrome.
Visual decision pathway
Shared placenta: detect, distinguish, escalate
TTTS, TAPS and selective growth restriction share a placental setting but require different measurements and decisions.
- ClassifyConfirm chorionicity early
Record placental sharing and amnionicity before later imaging obscures the signs.
- SurveyUse the monochorionic dataset
Fluid, bladders, growth, umbilical and cerebral Doppler, cardiac signs and cervix.
- DistinguishName the active mechanism
Separate TTTS fluid imbalance, TAPS anaemia–polycythaemia and unequal placental sharing.
- EscalateMatch stage to pathway
Close surveillance, active fetal treatment, delivery or another coordinated option.