zweieiige

Zweieiige, in medical terminology often called dizygotic twins, refers to a form of twinning that occurs when two separate eggs are fertilized by two separate sperm cells during the same pregnancy. The two resulting embryos develop independently and share about 50 percent of their genes, similar to typical siblings. They can be of the same sex or different sexes.

Genetically, zweieiige twins are not more alike than ordinary siblings. Because they originate from two zygotes, their genetic material is distinct, though they share the maternal environment during gestation. This form of twinning can occur in any pregnancy but is more common in certain populations and with specific risk factors.

Placentation and membranes are typically dichorionic diamniotic for zweieiige twins, meaning each twin usually has its own placenta and its own amniotic sac. This arrangement reduces the risk of some complications associated with shared placentation, but DZ pregnancies still carry higher rates of preterm birth and other maternal–fetal challenges compared with singleton pregnancies.

Incidence and risk factors: Zweieiige twinning is more common than monozygotic twinning and is influenced by maternal age (older mothers have higher rates), heredity in the maternal line, and the use of fertility treatments such as in vitro fertilization. A family history of fraternal twins increases risk for daughters, due to maternal inheritance of the tendency to release multiple eggs.

Diagnosis is usually via prenatal ultrasound, which shows two fetuses with separate placentas and sacs. The term zweieiige is used in German-language medical literature to describe this type of twinning.