Twin Pregnancy · Dhantoli, Nagpur

Chorionicity Scan in Twin Pregnancy in Nagpur

The scan that establishes whether your twins share one placenta or have two — performed and interpreted by Dr. Kunda Shahane, who also sets the monitoring plan that follows from it.

11⁺⁰–13⁺⁶ weeksUltrasound onlyScan, result and plan in one visitFMF (London) certified

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11–13⁺⁶Weeks — the reliable window

14+Years in fetal medicine

Mon–Sat10:00 AM – 6:00 PM

DhantoliNagpur – 440012

A chorionicity scan is the ultrasound that establishes whether twins share one placenta or have two. It is done between 11⁺⁰ and 13⁺⁶ weeks, and the answer decides the shape of the whole pregnancy: how often you are scanned, what is measured at every scan, and when the babies are delivered. Twins who share a placenta also share a circulation, and that produces complications which cannot occur in twins with separate placentas. At Mayflower Fetal Medicine & High-Risk Pregnancy Centre the scan is performed by Dr. Kunda Shahane herself, and the monitoring plan is written in the same visit.

Please note This scan establishes the number of placentas and amniotic sacs in a twin pregnancy. All ultrasound performed at this centre is carried out for medical diagnosis only, in full compliance with the PCPNDT Act, 1994.

Who performs this scan

Dr. Kunda Shahane is MBBS, MS (Obs & Gynae), FIFM, FMF (London) — an obstetrician and gynaecologist who then subspecialised in fetal medicine, with 20+ years in medicine and 14+ years in fetal medicine. She holds Fetal Medicine Foundation certification and follows FMF protocols for twin assessment.

That matters here more than on most scans. Determining chorionicity is a five-minute observation; deciding what to do about it is the rest of the pregnancy. The person who sees the T-sign is the same person who books your fortnightly scans, explains what twin-to-twin transfusion syndrome is before you have to read about it, and manages the maternal side of a twin pregnancy — blood pressure, thyroid, diabetes, anaemia — alongside the fetal side.

At a glance

When: 11⁺⁰ – 13⁺⁶ weeks; amnionicity from 8 weeks
How: Transabdominal ultrasound; transvaginal if needed
Duration: About 20–30 minutes
Preparation: None — no fasting, no full bladder
Recorded: An image of the intertwin septum, kept in your file
Decides: Scan interval, what is measured, timing of delivery

What chorionicity actually means

Chorionicity is the number of placentas. Dichorionic twins have one each. Monochorionic twins share one.

Amnionicity is the number of amniotic sacs. Monochorionic twins usually have a sac each — monochorionic diamniotic, or MCDA. A small number share a single sac — monochorionic monoamniotic, or MCMA, which is about 5% of monochorionic pregnancies and needs its own pathway.

Zygosity is whether the twins are identical or fraternal, and it is not the same question. Monochorionic twins are almost always identical. Dichorionic twins may be either, because identical twins that split early enough end up with a placenta each. Zygosity is confirmed after birth by laboratory testing, not by ultrasound.

Only chorionicity is a risk classification, which is why it is the one we establish first. Almost every monochorionic placenta contains vascular connections joining the two babies’ circulations, and it is the pattern of those connections that creates the risk.

How chorionicity is determined

ISUOG recommends that chorionicity be determined before 13⁺⁶ weeks using as many ultrasound features as possible: the entire intertwin septum where it inserts into the placenta, the thickness of the dividing membrane, and the number of placental masses.

The lambda sign — two placentas

Where the membrane meets the placenta, dichorionic twins show a wedge of placental tissue pushed up between two fused chorionic layers, with a thin amnion on each side. On screen it looks like a triangle filled in at the base — the full lambda, or twin peak.

The T-sign — one placenta

In a monochorionic diamniotic pregnancy only two thin amniotic layers separate the babies, and the membrane meets the placenta at a right angle with nothing inside it. The base may still look triangular, but it is empty — the empty lambda. Mistaking an empty base for a full one is the commonest way chorionicity is called wrongly, which is why the whole septum is examined and not just one point.

Counting placental masses is not enough on its own

Two separate-looking placentas do not rule out a shared circulation: about 3% of monochorionic pregnancies show two placental masses on ultrasound, and having two does not exclude the vascular connections between them. Dichorionic placentas that lie next to each other frequently look like one. The features are used together, never singly.

If you are already past 14 weeks

This is one of the commonest referrals we see: a woman arrives at 18 or 20 weeks with a report that says “twin pregnancy, both fetuses viable” and nothing else. The lambda sign becomes harder to find as pregnancy advances and has disappeared in a proportion of dichorionic pregnancies by 20 weeks, so the answer is no longer as reliable as it would have been at 12 weeks. It is still worth doing properly.

The same features are used, with more weight on carefully counting the layers of the dividing membrane, and transvaginal imaging is used where the transabdominal view will not settle it. If it still cannot be settled, ISUOG’s position is that the safest course is to classify the pregnancy as monochorionic. That is Dr. Kunda’s practice: the pregnancy is recorded as chorionicity undetermined and monitored on the monochorionic pathway. It is better to scan a dichorionic pair fortnightly for no reason than to scan a monochorionic pair monthly and find twin-to-twin transfusion syndrome late.

What the result changes

Dichorionic — two placentas

First-trimester scan, a detailed anomaly scan at around 20 weeks, and growth scans every 4 weeks after that. Umbilical artery Doppler from 24 weeks. The estimated weight difference between the twins is calculated and recorded at every scan from 20 weeks. Delivery is generally planned between 37⁺⁰ and 37⁺⁶ weeks.

Monochorionic diamniotic — one placenta

First-trimester scan, then a scan every two weeks from 16 weeks. At each one, the deepest pool of fluid around each baby is measured to screen for twin-to-twin transfusion syndrome. Umbilical artery Doppler and middle cerebral artery peak systolic velocity are recorded from 20 weeks, the latter to screen for twin anaemia–polycythaemia sequence. Fetal cardiac assessment is included. Delivery is generally planned between 36⁺⁰ and 36⁺⁶ weeks.

Monochorionic monoamniotic — one sac

Cord entanglement is present in nearly every monoamniotic pair and is identified on colour and pulsed-wave Doppler. These pregnancies need close, individualised surveillance and are delivered by caesarean section, usually between 32 and 34 weeks. Dr. Kunda manages monoamniotic twin pregnancies herself.

The gap between the two main pathways is the entire point of the scan. Fortnightly scanning from 16 weeks detects around 90% of twin-to-twin transfusion syndrome cases in time to act on them. A monochorionic pregnancy monitored on the dichorionic schedule can lose that window between one scan and the next.

What happens at the appointment

History and datingYour dates, how the pregnancy was conceived, and any previous pregnancies. In spontaneously conceived twins the pregnancy is dated from the larger crown–rump length; after 14 weeks, from the larger head circumference; and in IVF pregnancies from the embryo age and transfer date.
Labelling the twinsEach baby is described by position, placental site and cord insertion so that the same baby is identified as the same baby at every future scan. This is written into your notes and matters far more than it sounds — every growth comparison for the next six months depends on it.
The septumThe whole dividing membrane is followed to where it inserts into the placenta, and the lambda or T-sign, the membrane thickness and the number of placental masses are assessed together.
AmnionicityWhether there is a membrane at all. Where there is doubt, a transvaginal scan is used, and colour and pulsed-wave Doppler are used to look for cord entanglement.
The image goes into the fileAn image demonstrating the chorionicity is stored, as ISUOG recommends, so that no one later has to guess what the first-trimester scan showed. You get a copy.
The plan, in the same visitYou leave with the finding explained in plain language, the dates of your next scans, and what each of those scans is looking for. If your dates allow it, the nuchal translucency assessment is usually done at the same appointment.

What this scan does not do. Determining chorionicity does not prevent any complication — it decides how early one would be found. It is a classification, not a prediction: many monochorionic pregnancies run to term without incident, and dichorionic pregnancies have their own risks. Accuracy is highest before 14 weeks and falls after that. Ultrasound occasionally gets it wrong in both directions: in one series, around 5% of pregnancies that appeared monochorionic were later shown to be fraternal, which is more common after assisted conception. And no scan at any stage of a twin pregnancy can promise a healthy outcome for both babies. What it can do is make sure the right pregnancy is being watched the right way from 16 weeks onward.

The equipment, and why it matters here

Scans are performed on a GE Voluson Signature Expert (GE HealthCare). Chorionicity is decided on a structure two membranes thick, at a single insertion point, in a first-trimester uterus — it is a resolution problem more than anything else. High-frequency transabdominal and transvaginal probes, and the ability to store and re-examine the image afterwards rather than calling it from memory, are what the machine contributes to this particular scan. The same system carries the Doppler capability that the monochorionic pathway then depends on from 20 weeks.

Cost

A chorionicity assessment is not usually billed as a standalone item. It is part of a first-trimester twin scan, and what you pay depends on what is done in that appointment:

What is included	What changes the cost
First-trimester twin scan with chorionicity and amnionicity	Whether a transvaginal scan is needed
Dating, labelling and a stored image for your file	Whether nuchal translucency assessment is done at the same visit
Explanation of the finding and a written monitoring plan	Whether first-trimester screening bloods are added

Published scan charges for the centre are listed on the pregnancy scan cost page. For the exact figure for your appointment, WhatsApp 8087471244 with how many weeks pregnant you are.

Who looks after the pregnancy afterwards

A chorionicity result on its own is of no use to anybody. What it is for is the plan that follows it, and the same doctor who performs the scan writes that plan, counsels you about it, and carries it out — including the maternal side of a twin pregnancy, where hypertensive disorders, anaemia and diabetes are all commoner than in a singleton pregnancy.

If you are already booked with another obstetrician, that does not change: you are seen for the fetal medicine surveillance and referred back to your own gynaecologist with the findings and the schedule, which is the commonest arrangement in twin care. Women booked under Dr. Kunda’s own care have their delivery, including caesarean section, conducted by her at a hospital in Dhantoli.

How complete pregnancy care works here · Twin pregnancy monitoring · Monochorionic twin scan

Questions parents of twins ask

When should a chorionicity scan be done?

Between 11+0 and 13+6 weeks. This is the window in which the dividing membrane can be assessed reliably, because the amnion and chorion have not yet fused. If twins are found earlier, at 8 or 9 weeks, amnionicity can often be established then and chorionicity is confirmed at the 11 to 14 week visit.

What is the difference between chorionicity and amnionicity?

Chorionicity is the number of placentas and amnionicity is the number of amniotic sacs. Twins can have two placentas and two sacs, one placenta and two sacs, or one placenta and one sac. Chorionicity is the risk classification; amnionicity refines it further.

Does sharing a placenta mean something is wrong?

No. It means the pregnancy needs closer watching. Almost all shared placentas contain blood vessel connections between the two babies, and those connections can transfer blood unevenly. Most monochorionic pregnancies do not develop a serious complication, but the ones that do can change quickly, which is why scans are fortnightly rather than monthly.

Can this scan tell me whether my twins are identical?

Not with certainty. Twins sharing one placenta are almost always identical. Twins with separate placentas may be identical or fraternal, because an early split leaves each baby with a placenta. Zygosity is confirmed after birth by laboratory testing.

My report only says twin pregnancy. What should I do?

Bring it in. Chorionicity can still be assessed after 14 weeks, using the layers of the dividing membrane and transvaginal imaging where required, although it is less reliable than it would have been at 12 weeks. If it cannot be settled, the pregnancy is recorded as undetermined and monitored as though the babies share a placenta, which is the safer assumption.

How often will I be scanned?

If the twins have separate placentas, a first-trimester scan, an anomaly scan around 20 weeks and growth scans every four weeks after that. If they share a placenta, a scan every two weeks from 16 weeks, with amniotic fluid measured on both sides at each visit and Doppler measurements added from 20 weeks.

Can chorionicity change later in the pregnancy?

No. It is fixed at the time the pregnancy divides, in the first days after conception. What changes is how easily ultrasound can see it, which is why the first-trimester scan is not repeatable later.

Do I need to prepare for the scan?

No fasting and no full bladder. Wear something that allows access to the abdomen. Bring any previous scan reports, particularly the earliest one, and your IVF records if the pregnancy was conceived through treatment, because the dating method differs.

Will I need a transvaginal scan?

Sometimes. It is used when the abdominal view cannot show the membrane insertion clearly, which is more likely early in pregnancy or where the uterus is tilted. It is safe in pregnancy and takes a few extra minutes.

Can the nuchal translucency scan be done at the same visit?

Usually yes, because both are done in the same 11 to 14 week window. Screening for Down syndrome in twins is calculated differently from singletons and is more complex to interpret, so it is discussed with you before it is done rather than added automatically.

In Dr. Kunda’s words

Finding out you are having twins brings both joy and anxiety. For me, the most crucial first step is establishing 'chorionicity'—finding out if the babies share a single placenta or have their own. Knowing this early is absolutely essential, as it completely dictates how we monitor your pregnancy moving forward.

Dr. Kunda Shahane MBBS, MS (Obs & Gynae), FIFM, FMF (London)

Sources

Written and medically reviewed by Dr. Kunda Shahane, MBBS, MS (Obs & Gynae), FIFM, FMF (London) · Last reviewed: 9 September 2026

Twins on your scan? Get the chorionicity settled.

If you are between 11 and 14 weeks, this is the visit that sets up the rest of the pregnancy. If you are further along and no one has told you whether the babies share a placenta, it is still worth checking.

WhatsApp 8087471244 Call 0712 6692706 Book an appointment

Mayflower Clinic, Surdham Complex, Behind Silver Palace Building, 2nd Lane from Panchsheel Square, Opp. Yashwant Stadium, Dhantoli, Nagpur – 440012 · Monday–Saturday, 10:00 AM – 6:00 PM · Sunday closed

PCPNDT Act Compliance Notice Mayflower Fetal Medicine & High-Risk Pregnancy Centre strictly complies with the Pre-Conception and Pre-Natal Diagnostic Techniques (Prohibition of Sex Selection) Act, 1994. Sex determination and sex-selective practices are prohibited and punishable by law. Our ultrasound services are used exclusively for medical diagnosis. Disclosure of fetal sex is illegal and is not performed at this centre under any circumstances.

Medical Disclaimer This page is for general information and does not replace individual medical advice. Twin pregnancies vary, and the monitoring described here is adapted to each pregnancy. Ultrasound findings are interpreted alongside your history and examination. Always discuss your own situation with Dr. Kunda Shahane or your treating obstetrician.