Key takeaways
- Chorionicity, not whether twins are identical, is what determines the monitoring plan.
- It is most accurately identified at the 11–14 week scan, so an early scan is essential.
- Monochorionic twins share blood vessels in the placenta, which can cause TTTS in about 10–15% of these pregnancies.
- Two-weekly scans from 16 weeks allow TTTS to be detected and treated early.
- Recommended delivery timing differs: around 37 weeks for DCDA, 36 weeks for MCDA and 32–34 weeks for MCMA twins.
What is chorionicity and why does it matter?
Chorionicity describes whether twins have their own placenta (dichorionic) or share one (monochorionic). Amnionicity describes whether each baby has its own amniotic sac.
| Type | Placenta and sacs | How common | Main risks |
|---|---|---|---|
| DCDA (dichorionic diamniotic) | Two placentas, two sacs | About 70–80% of twins | Preterm birth, growth differences, pre-eclampsia |
| MCDA (monochorionic diamniotic) | One shared placenta, two sacs | About 20–30% | As above, plus TTTS, TAPS and selective growth restriction |
| MCMA (monochorionic monoamniotic) | One placenta, one shared sac | About 1% | As above, plus cord entanglement |
All non-identical twins are dichorionic. Identical twins can be any of the three types, depending on when the embryo split. On the early scan, a “lambda” or “twin peak” sign where the membrane meets the placenta suggests DCDA, while a thin “T” sign suggests MCDA. Accuracy is highest before 14 weeks, which is why an early scan matters so much.
What is TTTS (twin-to-twin transfusion syndrome)?
TTTS happens in monochorionic twins when blood flows unevenly through connecting vessels in the shared placenta. One twin (the donor) receives too little blood and the other (the recipient) receives too much.
On the scan, the donor twin has very little amniotic fluid and a small or empty bladder, while the recipient has excess fluid. It usually develops between 16 and 26 weeks and can progress quickly. Without treatment, severe TTTS carries a high risk of losing one or both babies, but with early detection and treatment outcomes are much better.
How is TTTS treated?
The main treatment for moderate to severe TTTS is fetoscopic laser surgery, which seals the connecting vessels on the placenta. It is done at specialised fetal medicine centres, usually between 16 and 26 weeks. Milder cases may be watched closely with frequent scans.
Other monochorionic complications
- TAPS (twin anaemia–polycythaemia sequence): a slower, uneven transfer of red blood cells, detected by Doppler measurement of blood flow in the baby’s brain.
- Selective fetal growth restriction: one twin is much smaller because of an unequal share of the placenta.
What is the scan schedule for twin pregnancy monitoring?
The schedule follows international guidance (such as NICE and ISUOG) and is adjusted if any problem is found.
| Twin type | Scan schedule | What is checked |
|---|---|---|
| DCDA | 11–14 weeks, anomaly scan at 18–22 weeks, then about every 4 weeks | Growth, fluid, growth difference between twins |
| MCDA | 11–14 weeks, then every 2 weeks from 16 weeks | Fluid, bladders, Doppler for TTTS and TAPS, growth |
| MCMA | Every 2 weeks from 16 weeks, often more closely later | As for MCDA, plus cord entanglement |
Cervical length may also be measured if there is a risk of preterm labour.
How can I look after myself in a twin pregnancy?
Expecting twins puts extra demands on your body, so a few practical steps help.
- Take iron, folic acid and calcium as prescribed; anaemia is more common with twins.
- Eat regular, balanced meals with extra protein; you need more calories than in a single pregnancy.
- Your doctor may advise low-dose aspirin, as twins raise the risk of pre-eclampsia.
- Rest when you can, and plan to reduce work in the third trimester.
- Learn the signs of preterm labour and know which hospital to go to.
When and how are twins delivered?
Planned delivery timing balances the risk of stillbirth late in pregnancy against the risks of prematurity.
Guidance generally recommends delivery from about 37 weeks for uncomplicated DCDA twins, 36 weeks for MCDA twins, and 32–34 weeks by caesarean for MCMA twins. Vaginal birth is often possible for DCDA and MCDA twins when the first baby is head-down. Twins should be delivered in a hospital with a NICU; see our guide on choosing a hospital for delivery.
When to see a gynaecologist
If you are expecting twins, contact your doctor or go to the labour ward urgently for:
- A sudden increase in tummy size, tightness or breathlessness (possible sign of TTTS)
- Regular contractions, back pain or pelvic pressure before 37 weeks
- Vaginal bleeding or leaking fluid
- Reduced movements of either baby
- Severe headache, blurred vision or sudden swelling
How Dr. Divya Venugopalan can help
Dr. Divya Venugopalan is an obstetrician and fertility specialist in North Bengaluru with more than 14 years of experience, a DNB in Obstetrics & Gynaecology and a Fellowship in Reproductive Medicine (FRM). Twin pregnancies are more common after IVF and ovulation induction, and she cares for many women through these pregnancies.
She makes sure chorionicity is recorded early, sets the right scan schedule and refers promptly to fetal medicine specialists if TTTS or other complications are suspected, as part of her high-risk pregnancy care. Read more about high-risk pregnancy management.
She consults at Thanisandra, Sahakar Nagar and HRBR Layout. Book an appointment or call +91 99459 26987.
Frequently asked questions
How do I know if my twins share a placenta?
An ultrasound between 11 and 14 weeks can show whether there is one placenta or two by looking at where the dividing membrane joins the placenta. Ask your doctor to record the chorionicity in your report.
Can identical twins have separate placentas?
Yes. About a third of identical twins split very early and have separate placentas (DCDA). Their monitoring is then the same as for non-identical twins.
How early can TTTS be detected?
TTTS usually develops between 16 and 26 weeks. Scans every two weeks from 16 weeks in monochorionic twins are designed to detect it early, when treatment works best.
Is a caesarean necessary for twins?
Not always. Many twins can be born vaginally if the first baby is head-down and there are no other complications. A caesarean is recommended for MCMA twins and in certain other situations.
Do twins always come early?
About half of twins are born before 37 weeks. Planned delivery is usually recommended at 36–37 weeks even when everything is going well, depending on the type of twins.
Medically reviewed by: Dr. Divya Venugopalan, MBBS, DNB (OBG), FRM, FMAS. Gynaecologist & fertility specialist, Bengaluru (KMC Reg. No. 91293). Last reviewed: 27 October 2026.
This article is for general information and does not replace a personal consultation. In an emergency, visit the nearest hospital emergency department.
