Monozygotinen

Monozygotinen, in German often used to refer to monozygotic twins, are individuals derived from a single fertilized egg that splits during early embryonic development. The resulting twins inherit nearly identical genetic material, including the same DNA sequence, although postzygotic mutations and epigenetic changes can introduce small differences over time.

The occurrence of monozygotinen is about 0.4 percent of all pregnancies, roughly 1 in 250 births. The timing of the embryonic split determines placentation and amnionicity. Splitting early can produce dichorionic diamniotic twins, while splits a few days later typically yield monochorionic diamniotic twins; splits around days 8 to 12 may lead to monochorionic monoamniotic twins, and splits after day 12 are rare and can result in conjoined twins.

Monochorionic twins share a single placenta and are at risk for placental-sharing complications, such as twin-to-twin transfusion syndrome (TTTS), growth discordance, and, in some cases, fetal demise. Monoamniotic combinations carry additional risks due to shared amniotic space, including cord entanglement. Because of these risks, pregnancies involving monozygotinen are generally managed as high-risk, with regular ultrasound surveillance and specialized obstetric care to monitor fetal growth and placental function.

Genetic identity in monozygotinen is not absolutely perfect; while twins are genetically very similar, differences can arise from somatic mutations and epigenetic modifications during development. Environmental factors and individual development can also lead to phenotypic differences, despite the shared genome. Assisted reproductive technologies are associated with a higher incidence of monozygotinen compared with spontaneous conceptions, though most cases occur without identifiable risk factors.