Chorionicity-Specific Care In Twin And Higher-Order Pregnancies

Multiple pregnancy is managed according to more than fetal number. The key distinction is chorionicity—the number of placentas—and amnionicity, meaning the number of amniotic sacs. These features determine how twins share blood flow, how often ultrasound is needed, which complications require urgent referral, and when birth should be planned.

For clinicians and families revisiting the scientific themes associated with FAOPS 2020 archive, chorionicity remains a practical foundation of perinatal medicine. The congress was scheduled in Tokyo alongside PREBIC AA 2020 before cancellation during the COVID-19 pandemic, yet its focus on fetal and neonatal research continues to reflect everyday decisions in Australian maternity services.

Why Placental Arrangement Matters

Dichorionic diamniotic twins usually have separate placentas and separate amniotic sacs. They can be fraternal or identical, although some identical twins divide early enough to develop this arrangement. Because each fetus has an independent placental circulation, twin-to-twin transfusion syndrome is not expected. Growth restriction, pre-eclampsia, antepartum haemorrhage and spontaneous preterm birth remain important risks.

Monochorionic diamniotic twins share one placenta but have separate sacs. Vascular connections between the fetal circulations create distinctive risks, including twin-to-twin transfusion syndrome, twin anaemia-polycythaemia sequence and selective fetal growth restriction. A problem affecting one fetus can also affect the other, so surveillance must assess both individual growth and the relationship between them.

Monochorionic monoamniotic twins share both a placenta and an amniotic cavity. Cord entanglement and cord compression add serious concerns. Higher-order pregnancies require the same principles, with further attention to the number of placentas, fetal positions, maternal symptoms, cervical length and the capacity of the maternity unit to provide timely intervention.

Confirming Chorionicity Early

The best time to determine chorionicity is the first-trimester ultrasound, generally between 11 and 14 weeks. Sonographers assess the membrane insertion, placental appearance and the lambda or twin-peak sign in dichorionic pregnancies. A thin dividing membrane and T-sign suggest monochorionic diamniotic twins, while the absence of a membrane supports a monoamniotic diagnosis.

The report should clearly record chorionicity and amnionicity, fetal number, crown-rump length, nuchal translucency where appropriate, and any structural findings. If the diagnosis is uncertain, the pregnancy should be managed conservatively as monochorionic until reviewed by an experienced fetal medicine specialist. Misclassification can lead to surveillance that is too infrequent for the actual risk.

Australian care is delivered across public hospitals, private obstetric practices and independent ultrasound clinics, with access varying between Sydney, Melbourne, Brisbane, Perth and regional centres. Medicare rebates may reduce the cost of some services, but out-of-pocket fees and appointment availability still influence care. Clear documentation helps when a family moves between providers or transfers from a rural hospital to a tertiary service.

Designing Ultrasound Surveillance

For dichorionic diamniotic twins, ultrasound commonly begins at regular intervals from around 20 weeks, often every four weeks if growth and fluid levels are reassuring. Scans assess estimated fetal weight, growth discordance, amniotic fluid, fetal anatomy and Doppler findings when clinically indicated. More frequent review may be needed when there is growth restriction, hypertension, abnormal placental function or reduced fetal movement.

Monochorionic diamniotic twins generally require ultrasound at least every two weeks from 16 weeks to screen for twin-to-twin transfusion syndrome. The assessment includes deepest vertical pockets of amniotic fluid, bladder filling, growth, umbilical artery Doppler and signs of cardiac strain. Some services also monitor middle cerebral artery Doppler to detect possible twin anaemia-polycythaemia sequence, particularly when clinical findings or previous complications raise concern.

Monoamniotic twins need specialist planning because ultrasound surveillance alone cannot remove the risk of sudden cord events. Assessment frequency and the timing of admission vary between units, gestational age and maternal preference. A woman living several hours from a tertiary hospital may need a different plan from someone close to a fetal medicine service in Adelaide or Canberra.

Blood pressure, urine protein, symptoms and general wellbeing should be reviewed alongside fetal ultrasound. The FAOPS resource on antenatal monitoring guidance is particularly relevant when a multiple pregnancy is complicated by hypertension, although local protocols and current evidence should guide decisions.

Recognising Complications Early

Twin-to-twin transfusion syndrome develops when unbalanced blood flow passes through placental vascular connections from a donor twin to a recipient twin. Reduced fluid and an absent bladder in the donor, together with excess fluid and cardiac strain in the recipient, should prompt urgent fetal medicine review. Fetoscopic laser treatment may be considered at specialist centres, depending on gestation, stage and clinical circumstances.

Selective fetal growth restriction in monochorionic twins is assessed using growth difference, abdominal circumference, fluid volume and Doppler patterns. The smaller twin may have limited placental territory, while the larger twin remains at risk if shared circulation becomes unstable. Management ranges from close surveillance to specialist intervention or planned early birth, depending on severity and gestation.

Pre-eclampsia, gestational diabetes, anaemia, venous thromboembolism and preterm labour are more common in multiple pregnancy. Aspirin prophylaxis may be advised for women at increased risk of pre-eclampsia, following an individual assessment and Australian guidance. A sudden increase in swelling, severe headache, visual disturbance, epigastric pain, bleeding, fluid loss or reduced fetal movement requires prompt clinical assessment.

Families should receive practical information about warning signs and access to care. In Australia, a patient who lives in a remote community may need to arrange transport, accommodation near a tertiary hospital and time away from work earlier than expected. These logistical details are part of safe management rather than an administrative afterthought.

Planning Birth And Newborn Care

Timing and mode of birth depend on chorionicity, amnionicity, fetal growth, Doppler results, maternal health, presentation and the presence of complications. Uncomplicated dichorionic pregnancies are often planned for birth around 37 to 38 weeks, while uncomplicated monochorionic diamniotic pregnancies are commonly delivered earlier, around 36 to 37 weeks. Monoamniotic pregnancies are usually delivered earlier still, often between 32 and 34 weeks, with an individualised plan.

These ranges are not substitutes for a local protocol. Australian hospitals differ in neonatal intensive care capacity, operating theatre availability, anaesthetic cover and experience with vaginal twin birth. A planned vaginal birth may be suitable when the first twin is cephalic and there are no contraindications, but counselling should cover the possibility of emergency caesarean birth for one or both babies.

Antenatal corticosteroids may be recommended when preterm birth is likely within the relevant treatment window. Magnesium sulfate for fetal neuroprotection may be considered at very early gestations, according to gestation-specific guidance. Birth planning should include neonatal consultation, blood bank arrangements, continuous fetal monitoring where indicated and a clear response plan for malpresentation or acute fetal compromise.

After birth, twins may need support with temperature control, glucose monitoring, feeding and respiratory transition. Parents benefit from discussing skin-to-skin care, expressing colostrum, lactation support and the possibility of neonatal unit admission before labour begins. In busy metropolitan hospitals, early coordination can prevent delays; in smaller services, planned transfer may be necessary.

Applying Care In Australian Practice

Clinical decisions should be individualised, documented and reviewed as the pregnancy evolves. The following priorities help align specialist recommendations with the realities of Australian maternity care:

• Confirm chorionicity and amnionicity in the first trimester, and arrange expert review if the ultrasound findings are uncertain.
• Use surveillance intervals appropriate to placental arrangement, with fortnightly assessment for monochorionic twins from the recommended gestation.
• Screen actively for pre-eclampsia, fetal growth restriction, twin-to-twin transfusion syndrome and preterm labour.
• Refer early to a fetal medicine or tertiary maternity service when complications arise or local neonatal resources are limited.
• Create a written birth and newborn-care plan that includes transport, corticosteroids, magnesium sulfate, anaesthesia and feeding support where relevant.

The comparison below provides a concise clinical framework, but it should be read with current RANZCOG advice, state or territory protocols and specialist recommendations. New evidence may alter surveillance schedules, intervention thresholds and delivery timing.

The most effective management combines accurate imaging, disciplined surveillance and rapid escalation when findings change. Families should receive information in plain language, with interpreters and culturally safe care when needed. Shared decisions are especially important when admission, invasive treatment, early delivery or prolonged neonatal care is being considered.

Antenatal planning should also respect Australian legal and ethical requirements. Informed consent, privacy obligations and state or territory rules apply to testing and treatment, while hospital policy governs referral and transfer arrangements. Clinicians should record the reasoning behind major decisions and ensure that parents know who to contact outside routine appointments.

Use chorionicity as the starting point for every twin or higher-order pregnancy assessment, then connect it to maternal health, fetal growth, local resources and the family’s circumstances. Reviewing current specialist guidance and establishing an early referral pathway can make surveillance more consistent and help Australian families reach the right level of care at the right time.