Chorionicity Scan in Twin Pregnancy in Nagpur
A chorionicity scan identifies whether twins have separate placentas or share one placenta. This single early ultrasound detail changes the entire pregnancy monitoring plan, especially the need for frequent scans in monochorionic twins.
One early diagnosis changes the whole twin pregnancy plan
The first question in a twin pregnancy is not only “are there two babies?” The more important fetal medicine question is: do they have separate placentas or a shared placenta?
Dr. Kunda Shahane evaluates chorionicity and amnionicity using the number of placental masses, membrane insertion, membrane thickness, lambda sign or T-sign, amniotic sacs and early fetal anatomy. This helps create the correct scan calendar from the beginning.
Chorionicity and amnionicity explained simply
Chorionicity tells us about the placenta. Amnionicity tells us about the amniotic sac.
Dichorionic diamniotic twins
Two placentas and two sacs. This is usually the lowest-risk twin type, though still higher-risk than singleton pregnancy.
Monochorionic diamniotic twins
One shared placenta and two sacs. These twins need closer surveillance for TTTS, TAPS and selective growth restriction.
Monoamniotic twins
One shared placenta and one shared sac. This is rare and needs very specialised high-risk pregnancy planning.
Uncertain chorionicity
If early images are missing or the report is unclear, expert review is important because management may change significantly.
Why early documentation matters
Chorionicity is easiest to determine in the first trimester. Later in pregnancy, placentas may appear fused and the inter-twin membrane may be difficult to interpret, so early scan images and reports are very valuable.
How chorionicity is assessed on ultrasound
A proper chorionicity scan uses multiple signs together, not just one quick view.
| Ultrasound feature | What is checked | Usually suggests | Why it matters |
|---|---|---|---|
| Number of placental masses | Whether there appear to be two separate placentas or one shared placental mass. | Two placentas: often dichorionic One placenta: review carefully | Separate vs shared placenta decides the surveillance frequency. |
| Lambda / twin-peak sign | A triangular projection of placental tissue at the base of the inter-twin membrane. | Usually dichorionic | Best seen early; supports DCDA classification when clearly present. |
| T-sign | The thin inter-twin membrane meets the placenta at a right angle without chorionic tissue between layers. | Usually monochorionic diamniotic | Suggests shared placenta and need for monochorionic surveillance. |
| Inter-twin membrane thickness | Thick membrane usually has more layers; thin membrane suggests fewer layers. | Thicker: dichorionic Thinner: monochorionic | Helpful when placenta number alone is not clear. |
| Presence or absence of membrane | Whether a clear membrane separates the twins. | No membrane: possible monoamniotic twins | Monoamniotic twins need very high-risk care and close planning. |
| Amniotic sacs | Whether twins are in two sacs or one shared sac. | Diamniotic vs monoamniotic | Amnionicity influences monitoring and delivery planning. |
| Early scan images and reports | Review of previous dating/NT scan images when current scan is late or unclear. | Essential if chorionicity is uncertain | Early images can prevent wrong classification and wrong monitoring schedule. |
Practical rule for patients
Every twin pregnancy report should clearly mention chorionicity and amnionicity. If your report says “twins” but does not mention placenta-sharing or sacs, it is worth getting the report reviewed by a fetal medicine specialist.
Why chorionicity changes the scan schedule
Dichorionic twins usually need serial growth and wellbeing monitoring. Monochorionic twins need closer surveillance because a shared placenta can lead to TTTS, TAPS, selective fetal growth restriction and sudden fluid or Doppler changes.
That is why chorionicity is not a small technical detail — it is the foundation of twin pregnancy management.
What happens after the chorionicity result?
If DCDA twins are confirmed
The pregnancy usually follows a dichorionic twin monitoring pathway with serial growth scans, anomaly scan, Doppler when needed and third-trimester wellbeing planning.
If MCDA twins are confirmed
A monochorionic surveillance pathway is planned, usually with scans every 2 weeks from around 16 weeks to screen for TTTS/TAPS and growth discordance.
If MCMA twins are suspected
This needs urgent high-risk counselling and coordinated planning with obstetric and neonatal teams because both babies share the same sac.
How chorionicity scan is performed at Mayflower
Review pregnancy dating and prior scans
Early ultrasound images, IVF records if applicable, previous twin scan reports and gestational age are reviewed first.
Assess number of placentas and sacs
The placenta, amniotic sacs, membrane and relationship between the twins are examined systematically.
Look for lambda sign or T-sign
The placental insertion of the inter-twin membrane is carefully assessed, especially in the first trimester.
Check early fetal wellbeing
Viability, dating, early fetal anatomy and any obvious discordance are documented for Twin A and Twin B.
Create the follow-up calendar
Based on chorionicity and amnionicity, the scan schedule is explained clearly to the family and referring obstetrician.
When should you book a chorionicity scan?
As soon as twins are detected
Do not wait until late pregnancy. The earlier chorionicity is recorded, the safer and clearer the monitoring plan becomes.
At 11–14 weeks
This is a very important window for dating, NT scan, early anatomy, chorionicity and amnionicity documentation.
If the report is unclear
If your report says “twin pregnancy” but does not mention DCDA, MCDA, MCMA, chorionicity or amnionicity, bring it for review.
Bring these reports
Bring the earliest pregnancy scan, any IVF/embryo transfer record if applicable, current ultrasound images, NT scan report, anomaly scan report if already done, and obstetric notes. Early images are especially useful for confirming chorionicity.
Dr. Kunda Shahane’s note on chorionicity
“In twin pregnancy, chorionicity is the first diagnosis that guides everything else. If twins share a placenta, the monitoring has to become more frequent and more detailed. A clear early chorionicity scan helps us protect both babies by choosing the right surveillance pathway from the beginning.”
Chorionicity scan FAQs
What is the difference between chorionicity and amnionicity?
Chorionicity tells whether twins have separate placentas or share one placenta. Amnionicity tells whether the twins have separate amniotic sacs or share one sac.
When is the best time to know chorionicity?
The first trimester is best, especially around 11–14 weeks, because the membrane and placental junction are easier to evaluate.
What does DCDA mean?
DCDA means dichorionic diamniotic twins — two placentas and two amniotic sacs. Sometimes placentas may appear fused later, which is why early confirmation is useful.
What does MCDA mean?
MCDA means monochorionic diamniotic twins — one shared placenta and two amniotic sacs. These twins need closer monitoring for TTTS, TAPS and selective growth restriction.
What does MCMA mean?
MCMA means monochorionic monoamniotic twins — one shared placenta and one shared amniotic sac. This is rare and requires specialised high-risk care.
What is the lambda sign?
The lambda or twin-peak sign is a triangular projection of chorionic tissue at the membrane insertion. When clearly seen early, it usually supports dichorionic twin pregnancy.
What is the T-sign?
The T-sign occurs when the thin inter-twin membrane meets the placenta without a chorionic peak. When clearly seen early, it usually supports monochorionic diamniotic twin pregnancy.
Can chorionicity be confirmed late in pregnancy?
It can sometimes be assessed later, but accuracy may be lower because placentas can appear fused and the membrane is harder to interpret. Early reports and images are very helpful.
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Need chorionicity confirmation in twin pregnancy?
Book a chorionicity and amnionicity scan with Dr. Kunda Shahane at Mayflower Fetal Medicine & High-Risk Pregnancy Centre, Dhantoli, Nagpur. Bring your earliest scan report and images so the twin pregnancy pathway can be planned correctly.
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