Finding out you are carrying twins changes everything about how your pregnancy will be managed. Not because something is wrong – but because two babies sharing one uterus need closer watching than one baby does.
A twin pregnancy is not simply a single pregnancy doubled. The scan schedule, potential complications and recommended timing of delivery can differ in a twin pregnancy. One important early step is determining whether the babies share a placenta, as this helps guide the monitoring plan.
This guide walks you through what happens at each stage, in plain language, so you know what to expect and what to ask for.
The First Scan: The One Question That Matters Most
Your first scan will confirm that there are two babies. But confirming twins is the easy part. The question that actually shapes the next eight months is chorionicity – whether the twins have separate placentas or share one.
There are three types:
Dichorionic diamniotic (DCDA) – two placentas, two sacs. This is the most common and the lowest risk of the three.
Monochorionic diamniotic (MCDA) – one shared placenta, two separate sacs. The babies share a blood supply, which brings specific complications that need close monitoring.
Monochorionic monoamniotic (MCMA) – one placenta, one sac, no membrane between the babies. This is rare and needs the most intensive care.
Chorionicity and amnionicity should ideally be determined and documented during the first-trimester ultrasound, generally between 11 and 14 weeks. If these cannot be established confidently, further assessment or a specialist opinion may be needed. The sonologist looks for a specific membrane sign where the membrane meets the placenta. After around 16 weeks, this sign becomes harder to see and the answer becomes less certain.
So if you are reading this early in a twin pregnancy, the single most useful thing you can do is get chorionicity formally documented before 14 weeks. A detailed assessment through advanced fetal ultrasound at this stage sets up the entire monitoring plan that follows – and if it was never documented in your case, a second opinion fetal ultrasound can still help clarify where you stand.
11 to 14 Weeks: The First Trimester Scan and Screening
At this scan, alongside chorionicity, three things are checked:
- Dating – in twins, the larger baby is usually used to set the due date
- Nuchal translucency (NT) – measured separately for each baby
- Early structural look – the basic anatomy of both babies
Screening for chromosomal conditions works a little differently in twins. In a single pregnancy, the combined screening test gives one risk figure. In twins, the risk is calculated for each baby separately, and the blood markers behave differently because two babies are contributing to them.
This is also why NIPT (the non-invasive prenatal test) performs differently in twins than in singletons. It can still be used, but the results need to be interpreted by someone who understands those limitations – it does not give the same clean answer it gives in a single pregnancy. If the screening comes back high risk for either baby, the next step is discussed properly rather than rushed, and options including invasive prenatal diagnostic testing are explained with the actual numbers, not vague reassurance.
Families who want to understand the screening pathway in more depth often find it useful to go through the full range of pregnancy screening tests available at this stage, and where there is a family history or a previous affected pregnancy, prenatal genetics and genetic counselling gives you a clearer picture before any decision is made.
16 to 24 Weeks: Where Monitoring Splits Into Two Paths
From 16 weeks onwards, the monitoring schedule depends entirely on chorionicity. This is where the two paths separate.
If the twins share a placenta (monochorionic)
You will need scans every two weeks from 16 weeks. This is not over-caution – it is the standard of care, and the reason is a condition called twin-to-twin transfusion syndrome (TTTS).
When twins share a placenta, they also share blood vessels within it. In about 10 to 15 percent of monochorionic pregnancies, blood flows unevenly from one baby to the other. One baby gets too much, the other too little. One sac fills with excess fluid, the other becomes nearly empty.
TTTS can develop quickly – sometimes within two weeks. That is exactly why the scans are fortnightly rather than monthly. Early detection can help the clinical team assess the condition and discuss appropriate management options. The available options depend on the severity of the condition, gestational age and specialist assessment.
Two related conditions are also watched for in shared-placenta twins: TAPS (twin anaemia-polycythaemia sequence), where the blood counts differ sharply between the babies, and selective fetal growth restriction, where one baby grows significantly slower than the other.
The important thing to understand is that these are findings that can be managed during the pregnancy itself in many cases – you do not always have to wait for delivery. Specialist assessment through fetal anomaly and therapy consultation is what determines whether intervention is needed and when.
If the twins have separate placentas (dichorionic)
TTTS is not a risk here, because there are no shared vessels. Monitoring is less frequent – usually growth scans every four weeks from around 24 weeks, with the anomaly scan at 18 to 22 weeks as in any pregnancy.
That said, dichorionic twins still carry a higher baseline risk of growth problems, preterm birth and preeclampsia than a single pregnancy. “Lower risk” means lower compared to monochorionic twins – not the same as a singleton pregnancy.
The Anomaly Scan in Twins: Why It Takes Longer
The detailed anatomy scan, done between 18 and 22 weeks, checks the structure of each baby – heart, brain, spine, kidneys, limbs, abdominal wall.
In a twin pregnancy this scan simply takes longer, because two complete examinations are being done in one sitting. It is also technically harder: the babies are positioned around each other, one may be lying in a difficult position, and views that come easily in a single pregnancy can take considerable patience.
Do not be alarmed if you are asked to come back for a repeat scan to complete some views. In twins this is common and does not mean something has been found.
24 to 32 Weeks: Growth, Cervix and Preterm Risk
This is the stretch where the focus shifts to two things – how well both babies are growing, and whether labour might start early.
Growth monitoring
Each baby is measured and plotted separately. What specialists watch for is not just whether each baby is growing well, but whether there is a significant difference between the two. A meaningful gap between the twins’ weights is a signal that needs investigation, especially in shared-placenta pregnancies.
Doppler studies – which assess blood flow in the umbilical cord and the baby’s circulation – become an important part of the assessment at this stage, particularly if growth is uneven.
Preterm birth
Around half of all twin pregnancies deliver before 37 weeks. This is the single most common complication in twins, and the one most worth planning for rather than reacting to.
Cervical length measurement during the mid-pregnancy scan helps identify who is at higher risk. Cervical length assessment can help identify an increased risk of preterm birth. If a short cervix is identified, your obstetrician can discuss appropriate management options based on your gestational age, medical history and current clinical guidance.
If you have had a previous preterm delivery, a previous pregnancy loss, or any other complicating factor alongside the twins, the pregnancy needs an integrated plan rather than separate opinions from separate specialists. That is what structured high risk pregnancy services are designed to provide.
Your own health
Twin pregnancies carry a higher chance of anaemia, gestational diabetes and preeclampsia (high blood pressure in pregnancy). Iron requirements are higher than in a single pregnancy. Blood pressure and urine are checked more frequently. In many twin pregnancies, low-dose aspirin started in the first trimester is recommended to reduce preeclampsia risk – your specialist will advise whether this applies to you.
32 Weeks to Delivery: Planning the Safest Exit
By this stage the conversation moves from monitoring to planning. Three questions get answered.
When will the babies be delivered?
The recommended timing of delivery in a twin pregnancy depends on chorionicity, the babies’ growth, any complications and the mother’s health. Planned delivery may be recommended before 40 weeks because the balance of risks changes as the pregnancy progresses. Your obstetric team can explain the timing appropriate for your pregnancy. General guidance is:
- Dichorionic twins – delivery usually planned around 37 to 38 weeks
- Monochorionic diamniotic twins – usually around 36 to 37 weeks
- Monoamniotic twins – much earlier, typically 32 to 34 weeks, by caesarean
These are planning ranges, not rules. Your own date depends on how both babies are growing, how the Dopplers look, and your own health.
Will it be a normal delivery or a caesarean?
This is the question most families ask first, and the honest answer is: it depends mainly on the position of the first baby.
If the first twin is head-down, vaginal delivery is often possible and reasonable, provided the pregnancy is otherwise uncomplicated and the delivery happens in a unit equipped to manage twins. If the first twin is breech or lying sideways, a caesarean is usually recommended.
A twin delivery, whichever route it takes, needs a prepared room – two neonatal teams, an anaesthetist available, and a unit with the capacity to escalate quickly. Planning this properly is a core part of multiple pregnancy care, and it is worth knowing where your delivery is planned well before you go into labour.
Where will the babies go after birth?
Twins are more likely than single babies to need some time in the neonatal unit, especially if delivered before 36 weeks. Knowing this in advance – and knowing that the hospital has NICU capacity on site – removes a great deal of anxiety on the day.
What You Should Actually Ask For
If you are pregnant with twins, these are the things to make sure are documented in your file:
- Chorionicity, confirmed in writing, ideally before 14 weeks
- A written scan schedule for the rest of the pregnancy, based on that chorionicity
- Separate growth charts for each baby, so differences are visible over time
- A cervical length measurement at the mid-pregnancy scan
- A planned delivery window and place, discussed before the third trimester
If any of these is missing, it is entirely reasonable to ask for it. A twin pregnancy managed with a clear plan is a very different experience from one managed scan by scan.
When to See a Fetal Medicine Specialist
The care plan for a twin pregnancy depends on the type of pregnancy and individual risk factors. Specialist fetal medicine assessment may be particularly important when:
- The twins share a placenta (monochorionic or monoamniotic)
- There is a noticeable growth difference between the babies
- The fluid levels differ between the two sacs
- Screening has returned high risk for either baby
- You have had a previous pregnancy loss or preterm delivery
- You have blood pressure, diabetes, thyroid or any other medical condition alongside the twins
Complex twin pregnancies often need more than one specialty working together – fetal medicine, neonatology, and sometimes genetics or cardiology. Bringing those opinions into one coordinated plan is the purpose of multidisciplinary fetal care, and the broader framework for it sits within maternal-fetal medicine as a specialty.
A twin pregnancy requires a care plan tailored to the babies’ development, chorionicity and the mother’s health. Early assessment, appropriate monitoring and timely discussion with the obstetric team can help families understand potential complications and plan for delivery. Individual outcomes vary, and the care plan may need to change as the pregnancy progresses.
Frequently Asked Questions
Is a twin pregnancy always high risk?
Twin pregnancies are classified as higher risk than single pregnancies, but risk varies considerably. Twins with separate placentas carry lower risk than twins sharing one. “Higher risk” means closer monitoring is needed – it does not mean a poor outcome is expected.
How many scans are needed in a twin pregnancy?
It depends on chorionicity. Twins with separate placentas typically need scans every four weeks from around 24 weeks. Twins sharing a placenta need scans every two weeks from 16 weeks onwards, to detect complications like TTTS early.
Are frequent ultrasounds safe in a twin pregnancy?
Yes. Diagnostic ultrasound used appropriately in pregnancy has no known harmful effects on the baby. In twin pregnancies the information gained from regular scanning clearly outweighs any theoretical concern.
Can twins be delivered normally?
Often, yes. It depends mainly on the position of the first baby, the type of twin pregnancy, and whether any complications are present. If the first twin is head-down and the pregnancy is otherwise uncomplicated, vaginal delivery can be considered in a properly equipped unit.
At how many weeks are twins usually delivered?
Twins with separate placentas are usually delivered around 37 to 38 weeks, and twins sharing a placenta around 36 to 37 weeks. Monoamniotic twins are delivered considerably earlier, by caesarean. The exact timing is individual.
What is TTTS?
Twin-to-twin transfusion syndrome occurs when twins sharing a placenta also share blood vessels, causing blood to flow unevenly between them. It affects roughly 10 to 15 percent of monochorionic pregnancies and is the main reason these pregnancies are scanned every two weeks.
