What Does It Mean When Twins Share One Placenta?
When twins share one placenta, they are called monochorionic twins. This usually happens when one fertilised egg splits into two embryos. These twins are generally identical. This arrangement occurs in about 70% of identical twin pregnancies and needs closer monitoring than a pregnancy where each twin has a separate placenta.
We spoke to Dr Soumya Lakshmi T V, Senior Consultant, Obstetrics & Gynaecology, Aster CMI Hospital, Bangalore, for verified expert insight on this.
Can Twins Share the Same Placenta?Only identical twins can share a placenta. Identical twins form when one fertilised egg splits into two embryos. Depending on how early the split happens, the twins may have two separate placentas or one shared placenta.
Fraternal twins, formed from two separate eggs fertilised by two separate sperm, always develop their own individual placentas and never share one. So a shared placenta is always a sign that the twins are genetically identical, not fraternal.
Doctors confirm this through an ultrasound scan done between 11 and 14 weeks of pregnancy. At this stage, the scan can identify the membrane pattern between the twins and determine whether they share one placenta (monochorionic) or have two separate ones (dichorionic). This scan window is considered the most accurate time to confirm the placental type.
Monochorionic twins fall into two types, based on whether they also share an amniotic sac:
What Are the Risks When Twins Share One Placenta?The shared placenta contains blood vessels that link the two babies' blood circulation. In most pregnancies, blood flow remains balanced. However, abnormal or uneven blood flow can cause complications.
Twin-to-twin transfusion syndromeTwin-to-twin transfusion syndrome (TTTS) is one of the most important complications of a monochorionic pregnancy. Blood flows disproportionately from one twin, called the donor, to the other, called the recipient.
The donor may have too little amniotic fluid, while the recipient may have excessive fluid. TTTS affects about 10–15%of twins sharing one placenta. Ultrasound monitoring helps doctors detect it early. In severe cases, doctors may use foetal laser therapy to seal off the abnormal connecting blood vessels in the placenta.
Twin anaemia-polycythaemia sequenceAnother possible complication is twin anaemia-polycythaemia sequence (TAPS). One twin can develop anaemia while the other develops an abnormally high concentration of red blood cells because of slow blood transfer through tiny placental connections. Doppler ultrasound can help detect changes in blood flow associated with TAPS.
Unequal growthUneven sharing of placental blood and nutrients can cause one twin to grow more slowly than the other. This is another reason growth measurements and blood-flow studies are performed regularly.
"Sharing one placenta does not automatically mean something will go wrong, and many pregnancies with monochorionic twins progress well when identified early and followed carefully by an obstetric team."
Dr Soumya Lakshmi, Sr. Consultant, Obs & Gyn, Aster CMI Hospital
How Is a Shared Placenta Diagnosed on Ultrasound?Doctors usually determine chorionicity, meaning whether the babies share a placenta, during an early pregnancy ultrasound. The first-trimester scan is particularly useful because the membrane between the babies and its attachment to the placenta can help identify the type of twin pregnancy.
A membrane that forms a characteristic “T-sign” suggests monochorionic twins, whereas a thicker membrane with a “lambda” or “twin-peak” sign suggests two placentas.
If the type of twin pregnancy is unclear during the first scan, additional ultrasound assessment may be needed.
With regular scans and timely specialist care, the majority of these twin pregnancies progress to the safe delivery of two healthy babies.
Whether you’re pregnant, a new mom, or navigating postpartum, you don’t have to do it alone. Join our support group to connect, share, and support one another.
FAQs on What Does It Mean When Twins Share One Placenta?Can twins who share a placenta be a boy and a girl?
No. Twins sharing one placenta are always identical and always the same sex, since they come from a single fertilised egg. How early can doctors tell if twins share a placenta?
Doctors confirm this on ultrasound between 11 and 14 weeks of pregnancy, since the signs become harder to identify as pregnancy progresses. Does sharing a placenta always cause complications?
No. Many monochorionic twin pregnancies progress with no major complications, though all are monitored more closely than pregnancies with separate placentas.
We spoke to Dr Soumya Lakshmi T V, Senior Consultant, Obstetrics & Gynaecology, Aster CMI Hospital, Bangalore, for verified expert insight on this.
Can Twins Share the Same Placenta?Only identical twins can share a placenta. Identical twins form when one fertilised egg splits into two embryos. Depending on how early the split happens, the twins may have two separate placentas or one shared placenta.
Fraternal twins, formed from two separate eggs fertilised by two separate sperm, always develop their own individual placentas and never share one. So a shared placenta is always a sign that the twins are genetically identical, not fraternal.
Doctors confirm this through an ultrasound scan done between 11 and 14 weeks of pregnancy. At this stage, the scan can identify the membrane pattern between the twins and determine whether they share one placenta (monochorionic) or have two separate ones (dichorionic). This scan window is considered the most accurate time to confirm the placental type.
Monochorionic twins fall into two types, based on whether they also share an amniotic sac:
- Monochorionic diamniotic (MCDA) twins: The most common type. The babies share one placenta, but each has a separate amniotic sac.
- Monochorionic monoamniotic (MCMA) twins: A rarer type. The babies share one placenta and the same amniotic sac.
| Type | Placenta | Amniotic sacs | Key concern | Typical monitoring | Typical delivery | Foetal Survival rate |
| MCDA twins | One shared placenta | Two separate sacs | Blood-flow complications such as TTTS | Fortnightly scans from around 16 weeks | Elective birth around 36-37 weeks | About 89% |
| MCMA twins | One shared placenta | One shared sac | Blood-flow problems plus umbilical cord entanglement | Fortnightly scans, plus inpatient monitoring from around 28 weeks | Elective caesarean around 32-34 weeks | About 78% |
Twin-to-twin transfusion syndrome
The donor may have too little amniotic fluid, while the recipient may have excessive fluid. TTTS affects about 10–15%of twins sharing one placenta. Ultrasound monitoring helps doctors detect it early. In severe cases, doctors may use foetal laser therapy to seal off the abnormal connecting blood vessels in the placenta.
Twin anaemia-polycythaemia sequenceAnother possible complication is twin anaemia-polycythaemia sequence (TAPS). One twin can develop anaemia while the other develops an abnormally high concentration of red blood cells because of slow blood transfer through tiny placental connections. Doppler ultrasound can help detect changes in blood flow associated with TAPS.
Unequal growthUneven sharing of placental blood and nutrients can cause one twin to grow more slowly than the other. This is another reason growth measurements and blood-flow studies are performed regularly.
"Sharing one placenta does not automatically mean something will go wrong, and many pregnancies with monochorionic twins progress well when identified early and followed carefully by an obstetric team."
Dr Soumya Lakshmi, Sr. Consultant, Obs & Gyn, Aster CMI Hospital
How Is a Shared Placenta Diagnosed on Ultrasound?Doctors usually determine chorionicity, meaning whether the babies share a placenta, during an early pregnancy ultrasound. The first-trimester scan is particularly useful because the membrane between the babies and its attachment to the placenta can help identify the type of twin pregnancy.
A membrane that forms a characteristic “T-sign” suggests monochorionic twins, whereas a thicker membrane with a “lambda” or “twin-peak” sign suggests two placentas.
If the type of twin pregnancy is unclear during the first scan, additional ultrasound assessment may be needed.
With regular scans and timely specialist care, the majority of these twin pregnancies progress to the safe delivery of two healthy babies.
Whether you’re pregnant, a new mom, or navigating postpartum, you don’t have to do it alone. Join our support group to connect, share, and support one another.
FAQs on What Does It Mean When Twins Share One Placenta?
No. Twins sharing one placenta are always identical and always the same sex, since they come from a single fertilised egg.
Doctors confirm this on ultrasound between 11 and 14 weeks of pregnancy, since the signs become harder to identify as pregnancy progresses.
No. Many monochorionic twin pregnancies progress with no major complications, though all are monitored more closely than pregnancies with separate placentas.
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