What to do if » Twins – multiple pregnancies
Multiple pregnancies carry higher risk. Specific expertise is a requisite for following such pregnancies.
In order to ensure that the most accurate calculation technique is used, the doctor will first have to establish the kind of multiple pregnancy he/she is dealing with.
Multiple pregnancies constitute almost 1% of all pregnancies. Two third of these are dichorionic (non-identical twins) while one third are monochorionic (identical).
Diagnosis of chorionicity
the best way to establish the chorionicity of a twin pregnancy by ultrasound at 11-13 weeks is by examining the junction between the membrane that separates the two fetuses and the placenta. In cases of dichorionic twins, you will be able to observe a triangular projection (lambda sign) of placental tissue inside the base of the membranes.
As the pregnancy progresses it becomes more difficult to identify the sign "lambda".
The outcome of the pregnancy is determined by whether the twins share the same placenta rather than whether they are identical or not.
Twins', Chromosomal abnormalities and Risk Calculation
Amniocentesis –Villocentesis in twins
Chorionicity and complications (BC= bicorial;MC= monocorial)
Miscarriage: In singleton pregnancies, where ultrasound shows a fetal viability of 11-13 +6 weeks, the probability of miscarriage or intrauterine fetal death before 24 weeks is about 1%. The risk of miscarriage in dichorionic twins is about 2% and in monochorionic twins of about 10%, the latter is mostly due to the twin-to-twin transfusion syndrome (TTTS).
Perinatal mortality: It is about 0.5% in singleton pregnancies, 2% in dichorionic twins and 4% in monochorionic twins. High mortality rate in multiple pregnancies is mostly due to complications that arise from premature delivery. In monochorionic twins, the risk is even higher due to twin-to-twin transfusion syndrome.
Growth restriction: In singleton pregnancies birth weight below the 5th percentile is generally 5%, in dichorionic twins is about 20% and in monochorionic twins of about 30%.
Pre-term deliver: Generally all babies born before the 24th week of pregnancy will die, while almost all those born after 32 weeks will survive. Babies born between 24 and 32 weeks are at high risk of neonatal death and disability. The risk of spontaneous delivery between 24 and 32 weeks is about 1% in single pregnancies, 5% in dichorionic twins and 10% in monochorionic twins.
Structural abnormalities: the likelihood of structural defects is about 1% in single pregnancies, 1% for each fetus in dichorionic twins and 4% for each fetus in monochorionic twins
Twin-to-twin transfusion syndrome
In all monochorionic pregnancies, there are vascular connections between the two fetuses in the placenta.
Twin-to-twin transfusion syndrome (TTTS) is caused by the blood flow through the placental vascular anastomoses from a fetus (donor) to another (the receiver).
In about 10% of monochorionic twin pregnancies severe TTTS, which is characterized by polyhydramnios (excess amniotic fluid) into the amniotic sac of the receiving fetus, can be observed within 16-24 weeks.
Another possible complication, which has been observed in approximately 10% of monochorionic twin pregnancies is severe growth restriction of one of the two fetuses.
Both TTTS and severe growth restrictions can be successfully treated with endoscopic laser surgery. This intervention breaks the connection between the blood vessels in the placenta.
Both TTTS and severe growth restriction can be predicted by the difference in the measurement of NT between the two fetuses at 11-13 weeks. The risk for developing these complications is 30% higher in pregnancies where the difference in NT measurements is equal or more than 20%. The risk is reduced to 10% where the difference in NT is less than 20%