Twins Formation and Types (Video Notes)

Vocabulary-style flashcards covering the types of twins, their formation, placental/amnionic considerations, and factors that affect twinning.

Fraternal twins (dizygotic)

Two eggs fertilized by two different sperm; two embryos; can be same or opposite sex; may not look alike.

Identical twins (monozygotic)

A single fertilized egg splits into two genetically identical embryos; usually the same sex.

Conjoined twins (Siamese)

Identical twins produced when splitting occurs incompletely, so the twins remain attached.

1 egg, 1 sperm (monozygotic)

A single fertilized egg splits to form two genetically identical individuals (identical twins).

2 eggs, 2 sperms (dizygotic)

Two eggs fertilized by two different sperms, forming two embryos (fraternal twins).

Early split

An early division of the zygote leading to twins that develop more independently.

Late split

A later division of the zygote leading to less independent development.

Placental relationship in twins

Identical twins typically share a placenta; fraternal twins usually have separate placentas.

Fraternal twins can be same or opposite sex

Because they come from two different eggs and sperms, they can be either both male, both female, or one of each.

Advancing maternal age

Older maternal age increases the chance of having twins.

Number of previous pregnancies (parity)

More previous pregnancies can increase the likelihood of twins.

Heredity

Family history can increase the chance of having twins.

Race

Black African women have the highest twinning rate; Asian women have the lowest.

Assisted reproductive techniques (ART)

Techniques like IVF increase the likelihood of having twins.