a. Multi-fetal pregnancy is a pregnancy involving two or more fetuses.
b. Twin fetuses may originate several ways (see figure 2-11).
(1) Identical twins (monozygotic) originate from the same ovum and are always of the same sex. They share a single placenta.
(2) Fraternal twins (dizygotic) originates from two separate ova and sperm and may be of different sexes. They each have their own placenta.
![Figure_2_11_Development_of_twin_fetuses_500 - Obstetric and Newborn Care I Figure 2-11. Development of twin fetuses.](https://brooksidepress.org/ob_newborn_care_1/wp-content/uploads/2015/05/Figure_2_11_Development_of_twin_fetuses_5001-300x249.jpg)
c. Pregnancies involving more than two fetuses (that is, triplets, quadruplets) may occur by either situation.
(1) Monozygotic–all will be identical.
(2) Multi-zygotic–often associated with fertility drugs in which the ovary matured and released many eggs in the same cycle.
![Twins - Obstetric and Newborn Care I Ultrasound image of twins in the first trimester](https://brooksidepress.org/ob_newborn_care_1/wp-content/uploads/2015/05/Twins-300x235.jpg)