Dizygoten

Dizygoten, or dizygotic, describes a pregnancy or individuals that arise from two zygotes formed when two eggs are fertilized by two separate sperm. It contrasts with monozygotic twinning, in which a single zygote splits to form identical twins. Dizygotic conceptions result from two ovulations in one cycle and two fertilizations, producing two genetically unique embryos.

During early gestation, two zygotes typically implant independently in the uterus, and the resulting pregnancy usually contains two placentas and two amniotic sacs (dichorionic diamniotic). In most cases each twin has its own chorion and amnion, though placental tissues may fuse over time and complicate imaging.

Genetically, dizygotic twins share about half of their segregating genes, like regular siblings, and can be of the same or different sexes. The twinning rate is influenced by maternal factors such as age and family history, and by assisted reproductive technologies; it also varies across populations and ethnic groups, being higher in some populations than others.

Clinical notes: Dizygotic twinning is a natural form of twinning but carries distinct risks inherent to multiple gestations, including potential discordant growth. Twin pregnancies require careful prenatal care because of risks such as preterm birth; certain complications, such as twin–twin transfusion syndrome, occur only in monochorionic pregnancies. Management depends on chorionicity, fetal growth, and maternal health.