MULTIPLE PREGNANCY
LEARNING OBJECTIVES
• At the end of the lecture, student should be able to:
– Define the multiple pregnancies.
– Know the different types of multiple pregnancies.
– Differences between the mono and dizygotic twins.
– Specify the risk factors related to multiple pregnancies
– Know about conjoined twins and its different types
MULTIPLE PREGNANCIES
• MULTIPLE PREGNANCIES consist of two or more
fetuses .
• TWINS make up the vast majority (97-98%) of multiple
gestations.
• PREGNANCIES with three or more fetuses are referred to
as ‘higher multiples’.
MULTIPLE PREGNANCIES
• Risk factors for multiple gestation include:
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Reproduction Techniques
(Both ovulation and in-vitro fertilization or IVF)
Increasing maternal age
High parity
Black Race
Maternal family history.
TWINS
• A twin is one of two offspring produced in the same
pregnancy.
• Twins can either be:
• Identical ("monozygotic") develop from one zygote that
splits and forms two embryos.
• Fraternal ("dizygotic") develop from two separate eggs that
are fertilized by two separate sperm.
Classification of multiple pregnancy
• Number of fetuses: twins, triplets, quadruplets, etc.
• Number of fertilized eggs: zygosity
• Number of placentas: chorionicity
ZYGOSITY
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Non identical or fraternal twins are dizygotic.
The fetuses can be either same-sex or different-sex-pairings.
Identical twins are monozygotic- and are always same-sex pairings.
Monochorionic twins may occasionally share a single sac (monoamniotic)
Approximately two thirds of twins are DIZYGOTIC.
TWINS AND FETAL MEMBRANES
• The fetal membranes and placentas vary according to the origin of twins.
• In the case of monozygotic twins, the type of placenta and membranes
formed depends on when the twinning process occurs.
DIZYGOTIC TWINS
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Result from fertilization of two oocytes.
May be of same sex or different sexes.
May or may not be identical in physical appearance.
Always have two amnions and chorions, but chorions
and placentas may be fused.
• Shows a hereditary tendency.
FRATERNAL TWINS
MONOZYGOTIC TWINS
• Result from fertilization of one oocyte.
• Same sex, genetically identical, very similar in physical appearance.
Divisions
 First 72 H  two embryos,
diamniotic, dichorionic and
two placenta or single fused
placenta.
 4-8 days  two embryos,
diamniotic, monochorionic.
 About 8 days after fertilization  two embryos,
monoamniotic and monochorionic.
 After 8 days conjoined twins result.
Risks of Multiple Fetal Pregnancy
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Abortion:
Increase spontaneous abortion more
than three times.
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Malformation:
Congenital malformation > single
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Low birth weight.
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Decrease duration of gestation:
a- 57% of twins  at 35 weeks.
b- 92% of triplets  at 32 weeks.
c- all quadruplets  at 29–30 weeks
Problems Specific to Monochorionic twins
Twin-Twin transfusion syndrome:* 15% of monochorionic develops.
* Early onset often is associated with poor
prognosis.
* Twin-Twin transfusion can be acute or
chronic.
* The net effect of blood flow imbalance
result:
a- donor  small, hypoperfused, anemic.
b- recipient  large, hyperperfused.
Problems for Monoamnionicity
Rare < 1% .
• Mortality 20-50%.
• Cord entanglement.
• Perinatal mortality. Preterm Delivery.
• Growth restriction.
• Congenital anomalies.
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Conjoined twins  Siamese twins
* Anterior (thoracopagus).
* Posterior (pygopagus).
* Cephalic (craniopagus).
* Caudal (ischopagus).
Conjoined Twins
• Most of conjoined twins occurred as a result of certain defects
occurred during separation of the cell-stage of first cleavage of
monozygotic twins.
• Connected to each other only by a common skin bridge or by a
common liver bridge (Siamese twins).
CLASSIFICATION OF CONJOINED TWINS
Types of Conjoined Twins
• Thoracopagus: Joined at the chest.
• The most common type of conjoined twins, representing 35% of all
conjoined twins.
• The heart is shared, and separation is rarely attempted for this reason.
• Omphalopagus: Joined at the abdomen.
• Similar to thoracopagus twins, but in this case the twins do not share a
heart.
• The second most common type of conjoined twins, representing 30% of
the total.
• Highest rate of separation survival. Usually, only the liver is involved.
Because the liver can regenerate itself, this scenario is preferred.
• Pygopagus: joined at the posterior pelvis.
• Separation possible. The survival rate is high.
Craniopagus(6%):
Fused skulls, but separate bodies.
These twins 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
• Separation is possible, depending on how much of
the brain is shared.
• High risk of brain damage.
REFERENCES
Keith L. Moore Developing Human
8th Edition
Chapter-7
Pages 134-135
THE END !!!!