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When a scan shows two heartbeats instead of one, everything changes in that room. Excitement, disbelief, and a rush of new questions follow almost straight away. One of the first things many parents want to know is whether they’re expecting identical or fraternal twins.
While many twin pregnancies progress normally, carrying twins can involve additional monitoring and may be considered a complicated pregnancy depending on the type of twins and any complications that develop.
This matters more than most people realise. It’s not just interesting to know; it actually affects the level of care and checking your pregnancy will need. Maternal-fetal medicine in Melbourne plays an increasingly important role in managing twin pregnancies. Understanding the basics behind your own pregnancy helps you take part in that care.
How Twins Form
Twin pregnancies happen in two different ways.
Fraternal twins, also called non-identical twins, happen when two separate eggs are fertilised by two separate sperm at the same time. Each baby grows in their own sac and has their own placenta. Fraternal twins share about 50% of their genes, the same as any brother or sister, and can be the same sex or different sexes.
Identical twins form when a single fertilised egg splits early on. When exactly it splits decides how the placenta and sacs are shared, which matters a lot for how the pregnancy is managed. Identical twins are always the same sex and share almost 100% of their genes.
Why the Placenta Matters So Much
Whether twins share one placenta or each have their own is called “chorionicity.” It is probably the single most important thing to know in twin pregnancy care. It’s best worked out at the first scan.
| Type | Placentas | Sacs | Risk Level |
|---|---|---|---|
| Dichorionic-diamniotic (DCDA) | Two, one each | Two, one each | Lower risk |
| Monochorionic-diamniotic (MCDA) | One, shared | Two, one each | Higher risk, needs close watching |
| Monochorionic-monoamniotic (MCMA) | One, shared | One, shared | Highest risk, most intensive care |
DCDA twins each have their own placenta and their own sac. All fraternal twins are DCDA. About a third of identical twins are also DCDA, when the egg splits within the first few days. DCDA is the lower-risk setup in twin pregnancy.
MCDA twins share one placenta, but each has their own sac. This is true for most identical twins. Sharing a placenta creates risks that simply cannot happen when twins have their own placentas.
MCMA twins are the rarest type. These identical twins share both a placenta and a sac. This creates the highest risk and needs the closest care, often with hospital admission in the third trimester.
Why This Matters So Much
The reason chorionicity gets so much attention is that twins sharing a placenta can develop problems that simply can’t happen when twins each have their own.
Twin-to-Twin Transfusion Syndrome (TTTS)
TTTS occurs in shared-placenta pregnancies when abnormal blood vessels within the placenta distribute blood unevenly between the twins. The donor twin can become low on blood and grow more slowly. The twin receiving too much blood ends up with an overloaded system and too much fluid around them.
TTTS can develop fast and is serious, needing specialist treatment. Treatment, usually done at a fetal medicine centre, uses a laser to seal off the abnormal vessels. Without treatment, outcomes can be poor.
Uneven Growth Between Twins
When blood flow through a shared placenta isn’t even, one twin may get a lot less food and oxygen than the other. This can lead to intrauterine growth restriction (IUGR), which needs close watching and careful decisions about when to deliver.
Twin Reversed Arterial Perfusion (TRAP)
TRAP is a rare problem in shared-placenta twins where one twin doesn’t have a working heart and survives only on blood from the healthy twin. This puts a huge strain on the healthy twin’s heart and needs specialist care.
Checking on Twin Pregnancies
Both types of twin pregnancy need more frequent checking than a single-baby pregnancy, though the details differ a lot.
For DCDA twins, growth scans usually occur every 4 weeks from around 20 weeks, plus extra checks of the baby’s well-being in the third trimester.
For MCDA twins, scans usually happen every two weeks from around 16 weeks, to catch early signs of TTTS or uneven growth. This is often needed because TTTS can develop and get worse quickly between visits.
For MCMA twins, checking is the most intense, and many obstetricians suggest planned hospital admission in the late third trimester because of the risk of the babies’ cords tangling.
Getting experienced maternal-fetal medicine care in Melbourne when problems arise means specialists with a real depth of knowledge read tricky findings.
Is My Twin Pregnancy Identical or Fraternal?
Many parents want to know early, and the first-trimester scan is the best time to find out chorionicity. After the first trimester, it gets harder to be sure.
If the twins are different sexes, they are definitely fraternal. If they’re the same sex, chorionicity checked on ultrasound is the best guide during pregnancy. A DNA test after birth can confirm this for certain, but the chorionicity identified on ultrasound is what matters most clinically during pregnancy.
Specialist Care for Twin Pregnancies
Twin pregnancies classed as a high-risk pregnancy in Melbourne do best with steady specialist care right through the pregnancy and into birth planning.
Dr Steven Hatzikostas is an experienced obstetrician with a lot of hands-on experience managing twin pregnancies, including both DCDA and MCDA twins. He offers thorough, personal antenatal care in Melbourne for families expecting twins, with a checking schedule matched to the exact type of twins and any problems that come up.
As a private obstetrician in Melbourne, Dr Hatzikostas offers 24/7 access for his obstetric patients. This matters a lot for families managing the intense checking schedule of a shared-placenta twin pregnancy.
Conclusion
The difference between identical and fraternal twins is not just something to know for its own sake. It has a direct effect on how closely your pregnancy is watched, what problems to look out for, and how birth is planned.
Dr Steven Hatzikostas offers experienced, attentive obstetric care for families expecting twins across Melbourne, making sure the type and pace of checking matches the actual risks of your twin pregnancy. If you’ve just found out you’re expecting twins, seeing a specialist early helps make sure your care plan is clear from the very start.
Frequently Asked Questions
When is the best time to find out if twins are identical or fraternal?
The best time is at your first-trimester scan, usually between 11 and 14 weeks. The placenta and sac details are clearest at this point. After the first trimester, it becomes harder to be sure of chorionicity.
Can identical twins have different blood types?
No. Identical twins share the same genes, including blood type. If twins have different blood types, they are definitely fraternal.
What is Twin-to-Twin Transfusion Syndrome and how common is it?
TTTS only happens in shared-placenta twin pregnancies, affecting about 10 to 15 out of every 100 MCDA twin pregnancies. It means blood passes unevenly between twins through abnormal vessels in the shared placenta. It can develop fast and needs specialist treatment.
Do twins need to be born early?
It depends on the type of twins and whether any problems have come up. DCDA twins are often born around 38 weeks. MCDA twins may be born earlier, around 36 to 37 weeks, and MCMA twins are often born even earlier because of cord risks. Your obstetrician will talk through timing based on your own pregnancy.
Is a vaginal birth possible with twins?
Often, yes. If both twins are head-down, a vaginal birth may be possible. If the first twin isn’t head-down, or if serious problems have come up during the pregnancy, a caesarean is usually recommended. Birth planning for twins is always worked out for your specific situation.
