Twin Pregnancies: Importance of Prenatal Diagnosis

Twin pregnancies have increased in recent decades due to assisted reproductive techniques and delayed childbearing. However, there are risks involved, as there are more miscarriages and preterm deliveries. Prenatal diagnosis is essential to know the state of the embryos and possible malformations.

Twin pregnancies: increase in the number of cases. Why?

Multiple gestation has undergone a clear increase in recent decades. According to the National Institute of Statistics (INE), in the year 2000 in Spain there were 386,336 single births compared to 5975 twin pregnancies. The latest available data is from 2012, where there were 436,096 single births and 9,796 twin births in Spain.

In the Region of Murcia there has been a similar evolution. In 2000, the number of singleton births was 13,726 versus 253 twin births, while in 2012, there were 16,140 singleton births and 298 twin births.

Among the factors related to the increase in twin births we have:
– reproductive techniques, since naturally only 2% of pregnancies are twins, while about 25% of pregnancies achieved with reproductive techniques are twins.
– Delayed childbearing, since the natural conception of twin pregnancies increases 4 times between the ages of 15 and 35.

Types of twin pregnancies

It is important to distinguish between dichorionic twin gestation (BC, 2 placentas) or monochorionic (MC, a single placenta, which in turn can be biamniotic or monoamniotic). This diagnosis is made in the first trimester of gestation, usually between 11-13 weeks, together with the diagnosis of malformations or chromosomopathies. Chorionicity, i.e. the number of placentas, will determine the prognosis and outcome of the pregnancy.
Compared to singleton pregnancies, there is an increased rate of miscarriage before the first week of pregnancy.
– miscarriage rate before the 24th week (1% in singleton pregnancies, 2% in BC and 10% in MC)
– perinatal mortality above 24 weeks gestation (0.5% in singletons, 2% in BC and 4% in MC),
– growth restriction below the 5th percentile (5% in singletons, 20% in BC and 30% in MC)
– preterm delivery (1% in singletons, 5% in BC and 10% in CM)
– chromosomal abnormalities (1% in singletons, 1% in BC and 4% in CM).

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In addition, in monochorionic twins there are other added and serious complications, such as the development of feto-fetal transfusion syndrome or TRAP sequence.
Monoamniotic monochorionic twins, in addition to the complications mentioned above, have a high risk of fetal death due to umbilical cord intertwining problems.

Importance of prenatal diagnosis in twin pregnancies

Prenatal diagnosis carried out by experts in Gynecology and Obstetrics is essential to know the chorionicity, fetal malformations, preterm delivery and other possible complications related to multiple gestation. For this it is necessary to perform serial ultrasounds, which vary depending on whether there is one or two placentas, although the most important are those at 12 (between 11-13 weeks) and 20 weeks, both key for the diagnosis of malformations and screening for chromosomopathies, fundamentally.

In short, twin gestations have more added complications. One of the most important is preterm delivery, that is, before 37 weeks. About 50% of these pregnancies end in preterm delivery. Neonatal morbimortality varies according to gestational age, with the prognosis being much worse the younger the gestational age at birth. Therefore, it is essential to continue research to reduce preterm delivery in this type of pregnancy, but it is also essential to have good Neonatal Care Units, where the newborn will be cared for and attended, resolving possible complications derived from gestational age and birth weight.