Multiple Pregnancies Flashcards
● A pregnancy in which the woman is carrying two or
more fetuses
● Considered a complication of pregnancy
It is sometimes difficult to determine by sonogram
or at birth whether twins are identical or fraternal
MULTIPLE PREGNANCY
1.) Multiple (typically two) fetuses produced by the
splitting of a single zygote
2.) Multiple (typically two) fetuses produced by two
zygotes
3.) Multiple fetuses produced by two or more zygotes
1.) Monozygotic
2.) Dizygotic
3.) Polyzygotic
● Also known as Siamese twins
● Identical twins whose bodies are joined in utero
● Higher incidence (Southwest Asia & Asia)
● Overall survival rate: approx. 25%
● Frequently found among females
CONJOINED TWINS
1.)
Older & most generally
accepted theory which
the fertilized egg splits
partially
2.)
A fertilized egg
completely separates, but
stem cells (which search
for similar cells) find
like-stem cells on the
other twin and fuse the
twins together
1.) FISSION
2.) FUSION
● Two faces on opposite sides of a single, conjoined
head
● Upper portion of the body is fused while the
bottom portions are separate
● Generally cannot survive
● Also known as janiceps or syncephalus
CEPHALOPAGUS
Bodies fused in the head and thorax
● Has two faces facing the opposite directions or
sometimes a single face and enlarged skull
CEPHALOTHORACOPAGUS
● 18.5% of cases
● 2 bodies fused from the upper thorax to lower
belly
● The heart is always involved in these cases
THORACOPAGUS
● 10% of cases
● Two bodies fused at the lower chest
● Unlike thoracopagus, the heart is never involved
● Twins share a liver, digestive system, diaphragm,
and other organs
OMPHALOPAGUS
● 28% of cases
● 2 bodies fused from the upper chest to lower
chest
● Twins usually share a heart, and may also share the
liver or part of the digestive system
THORACO-OMPHALOPAGUS
2 bodies fused in the xiphoid cartilage – these
twins almost never share any vital organs, with the
exception of the liver
XIPHOPAGUS
Fused lower half of the two bodies, with spines
conjoined end-to-end at a 180% angle. These
twins have four arms; two, three, or four legs; and
typically one external set of genitalia and anus
ISCHIOPAGUS
Fused in a similar fashion as ischiopagus twins, but
facing each other with a joined abdomen akin to
omphalopagus. These twins have four arms, and
two, three, or four legs
OMPHALO-ISCHIOPAGUS
● Fused side-by-side with a shared pelvis
● Has 3 sub-types:
○ Dithoracic parapagus - fused at the abdomen
and pelvis, but not the thorax
○ Diprosopic parapagus - have one trunk and
one head with two face
Dicephalic parapagus - have one trunk and
two heads, and two-four arms
PARAPAGUS
● 6% of cases
● Fused skulls, but separate bodies
● Can be conjoined at the back of the head, the front
of the head, or the side of the head, but not on the
face or the base of the skull
CRANIOPAGUS
Two bodies joined at the pelvis
PYGOPAGUS (ILIOPAGUS)
● Fused dorsally above the sacrum & lumbar spine,
involving different segments of the column
● Rare occurrence
RACHIPAGUS
Twins that are asymmetrically conjoined, resulting
in one twin that is small, less formed, and
dependent on the larger twin for survival
PARASITIC TWINS
● Situation in which an undeveloped fetus in encased
in the body of its twin
● Often presents as a cyst
FETUS IN FETU
One head w/ a single face but four ears, and two
bodies
SYNCEPHALUS
