What are the main types of twins?

The two main types are monozygotic (identical) twins, which form from a single fertilized ovum that splits, and dizygotic (fraternal) twins, which result from fertilization of two separate ova by two separate sperms.

How do dizygotic twins differ from monozygotic twins?

Dizygotic twins are genetically as similar as siblings, can be of the same or different sex, and have separate placentas, chorions, and amniotic sacs. Monozygotic twins are genetically identical, always the same sex, and may share placenta and/or membranes depending on the timing of division.

What determines the fetal membrane arrangement in monozygotic twins?

The arrangement depends on the timing of embryonic division: early split leads to two amnions, two chorions, and two placentas (may fuse); later split leads to two amnions, one chorion, and one placenta (most common); late split leads to one amnion, one chorion, and one placenta.

What are conjoined twins, and how are they classified?

Conjoined (Siamese) twins result from incomplete separation of the embryoblast, leading to fused twins. They are classified by the fusion site, such as craniophagus (heads fused), thoracophagus (thoraces fused), cephalothoracophagus (head and thorax fused), or pygophagus (sacral regions fused).

What is a parasitic twin?

A parasitic twin is an underdeveloped twin dependent on the better-formed co-twin. In some cases, it may be enclosed within the body, termed fetus in fetu.

What are the clinical risks associated with twinning?

All types of twins have increased risks, including preeclampsia, prematurity, and congenital anomalies.

What is erythrocyte mosaicism in twins?

Erythrocyte mosaicism can occur in dizygotic twins when their placentas are close and fuse, allowing for red cell exchange between the twins.

Twinning – Monozygotic vs Dizygotic & Membranes

❓ Frequently Asked Questions