Understanding the Different Types of Twin Pregnancy
Twin pregnancy is a unique and exciting journey for expecting parents. While carrying twins is joyful, it is also medically different from a single pregnancy. One of the most important aspects doctors evaluate in twin pregnancy is how the babies are formed inside the uterus, specifically how they share the placenta and the amniotic sac.
At Nisarga Diagnostics, Bengaluru, early and accurate ultrasound examination plays a key role in identifying the type of twin pregnancy, helping doctors plan appropriate follow-up scans and care throughout pregnancy.
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Why Is It Important to Know the Type of Twin Pregnancy?
Not all twin pregnancies are the same. The way twins share:
- Placenta (chorion) – which supplies blood, oxygen, and nutrients
- Amniotic sac (amnion) – the fluid-filled protective chamber
determines how the pregnancy is classified.
This classification helps obstetricians:
- Understand fetal development
- Decide scan frequency
- Monitor growth patterns
- Guide parents with correct information
Early pregnancy ultrasound is the most reliable way to determine this
Basics: Placenta, Amniotic Sac, and Blood Supply
Before understanding the types, it is useful to know a few basics:
- Placenta is the organ that supplies oxygen and nutrients from the mother to the baby.
- Umbilical cord connects each baby to the placenta.
- Amniotic sac is the fluid-filled space that cushions and protects the baby.
Depending on how early the embryo divides, twins may have:
- Separate placentas
- A shared placenta
- Separate or shared amniotic sacs
Based on this, twin pregnancies are divided into three main types.
1. Dichorionic Diamniotic Twin Pregnancy
What Does This Mean?
- Two placentas
- Two amniotic sacs
- Each baby develops in its own separate chamber
This is the most common type of twin pregnancy.
How Blood Supply Happens
Each baby has:
- Its own placenta
- Its own umbilical cord
- An independent blood supply
There is no sharing of blood circulation between the babies. Even if the placentas appear fused on ultrasound, they function separately.
How This Type Forms
- Always seen in fraternal (non-identical) twins
- Can also occur in identical twins if the embryo divides very early (within the first 3 days after fertilization)
Ultrasound Findings
- Two placentas
- A thick dividing membrane between babies
- Clearly separate amniotic sacs
2. Monochorionic Diamniotic Twin Pregnancy
What Does This Mean?
- One shared placenta
- Two separate amniotic sacs
- Babies have their own fluid chambers but share the placenta
This type occurs only in identical twins.
How Blood Supply Happens
- Both babies receive blood from one common placenta
- Each baby has its own umbilical cord
- Inside the placenta, blood vessels may connect
Although the babies are separated by a thin membrane, the shared placenta means blood circulation comes from a single source.
How This Type Forms
- Occurs when a single fertilized egg divides between 4–8 days
- Results in identical twins with shared placental support.
Ultrasound Findings
- Single placenta
- Thin dividing membrane between babies
- Two separate amniotic sacs
Special attention during ultrasound is required to identify this accurately.
3. Monochorionic Monoamniotic Twin Pregnancy
What Does This Mean?
- One placenta
- One amniotic sac
- Both babies share the same chamber
This is a rare type of twin pregnancy.
How Blood Supply Happens
- Both babies receive blood from one placenta
- There is no dividing membrane
- Umbilical cords share the same space
Because the babies are in a single fluid chamber, their movements occur together in the same environment.
How This Type Forms
- Occurs when the embryo divides after 8 days
- Always seen in identical twins
- Very uncommon compared to other twin types
Why Extra Care Is Needed
Since both babies share:
- The same placenta
- The same amniotic sac
- The same physical space
This type of twin pregnancy requires very careful and close monitoring.
At Nisarga Diagnostics Bengaluru, early identification allows doctors to:
- Plan frequent ultrasound evaluations
- Closely observe fetal movements and growth
- Coordinate care with the treating obstetrician
Role of Ultrasound in Twin Pregnancy
Early ultrasound plays a critical role in twin pregnancy by helping doctors:
- Identify the number of placentas
- Identify the number of amniotic sacs
- Classify the type accurately
- Track growth patterns of both babies
Ideal Time for Classification
- Best done between 11–14 weeks
- Early scans provide the clearest view of membranes and placental structure
Summary of Twin Pregnancy Types
Twin Pregnancy Type | Placenta | Amniotic Sac | Baby Space |
Dichorionic Diamniotic | Two | Two | Separate chambers |
Monochorionic Diamniotic | One | Two | Separate chambers |
Monochorionic Monoamniotic | One | One | Same chamber |
Final Thoughts
Twin pregnancy is a beautiful and unique journey. Understanding how twins develop inside the uterus, how they share the placenta, and how their living space is formed helps parents and doctors work together for smooth pregnancy care.
Early and accurate diagnosis through ultrasound is essential for proper classification. For reliable twin pregnancy ultrasound scans in Bangalore, expert imaging, and diagnostic support, Nisarga Diagnostics continues to be a trusted name among expectant parents and healthcare providers.
Founder of Nisarga Diagnostics, is a renowned fetal ultrasound specialist with over 20 years of expertise. An alumnus of Government Medical Colleges in Mysore and Bangalore, he also holds a D.N.B. from the National Board of Examinations, Delhi, and certification from the Fetal Medicine Foundation, London. A former Professor and HOD, he has trained countless PG students and junior radiologists, shaping the future of fetal imaging in India.