Description of genesis of twins

                                  Genesis of twins

A. Dizygotic twins - 

Dizygotic twins results from fertilization of two ova, most likely ruptured from two distinct graafian follicles usually of the same or one from each ovary, by two sperms during a single ovarian cycle. Their subsequent implantation and development differ little from those of a single fertilized ovum.

B. Monozygotic twins (identical) -

The twinning may occur at different periods after fertilization and this markedly influences the process of implantation and the formation of the fetal membranes. After the fertilization, the following possibilities may occur -

• If the division takes place within 72 hours after fertilization (prior to morula stage) the resulting embryos will have two separate placenta, chorions and amnions (diamniotic - dichorionic or D/D)

• If the division take place between the 4th and 8th day after the formation of inner cell mass when chorion has already developed - diamniotic monochorionic twins develop (D/M).

• If the division occur after 8th day of fertilization when the amniotic cavity has already formed, a monoamniotic - monochorionic twins develops (M/M).

• Rare occasion, division occurs after two weeks of the development of embryonic disc resulting in the formation of conjoined twins called siamese twins. Four types of fusion may occur -

       i) Thoracopagus - conjoined twins at the thorax.

       ii) Pyopagus - conjoined twins at the posterior site.

       iii) Craniopagus - twins joint at the head.

       iv) Ischiopagus - twins joint at the ischeum.


Related articles :

• Multiple pregnancy (Twins)
• Causes of genesis of twins
• Management of twin pregnancy
• What is Superfetation and Superfecundation