2. Introduction
Most twins are fraternal or identical, but there are
additional subtypes, including mirror twins and
conjoined twins, that are rare. In fact, twins account
for about 32 of every 1,000 births, according to the
most recent data from the Centers for Disease
Control and Prevention (CDC). And for some
women, their chances for having multiples could
skew even higher!
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3. Twins - Monozygotic
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• Identical twins, or monozygotic twins, form when one fertilized egg
splits in two and grows into two separate embryos. The twins are
the same gender, share the same blood type, and share the same
physical traits. Identical twins may or may not share one amniotic
sac.
• One of the most common questions asked is “Do identical twins
have the same DNA?” They actually do have the same DNA at
birth but eventually the DNA becomes more distinctive based on
environmental factors. This is how each twin evolves to be a
unique individual.
6. Twins - Dizygotic
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• Fraternal twins, which are also called dizygotic twins, are the result
of two separate eggs being fertilized by two separate sperm. This
can happen because the ovaries release two eggs and not just
one.
• Basically, fraternal twins are as alike as siblings would be — in
other words, they are not identical. Fraternal twins might be two
boys, two girls, or a boy and a girl. Each baby develops in his or
her own placenta.
9. Do Twins Share a Placenta and
Amniotic Sac?
Sometimes twins share the placenta (the organ that connects mother to
baby), amniotic sac (the inner membrane), and chorion (the outer
membrane), and sometimes they each have their own. Your healthcare
provider will be able to explain which of these is relevant for your
pregnancy, and what it might mean for your pregnancy and babies.
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10. Diamniotic-dichorionic Twins
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These types of twins
have their own chorions
and amniotic sacs, but
they may or may not
share the same
placenta.
12. Monoamniotic-monochorionic Twins
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These types of twins share a
chorion, placenta, and an
amniotic sac. This is the
rarest type of twin, and it
means a riskier pregnancy as
the babies can get tangled in
their own umbilical cords. If
you have monoamniotic-
monochorionic twins, your
healthcare provider will
monitor your pregnancy
13. OTHER TYPES OF TWINS :
MIRROR TWINS
Twins whose features appear asymmetrically—that is, on opposite
sides. When these twins are facing each other, it is as if they are
looking in a mirror. Eg ; moles, nostrils, eyebrows etc …
SEMI-IDENTICAL TWINS
Semi-identical twins, or sesquizygotic twins, are a rare type
of twins that result from the fertilization of one egg by two
sperm. The egg then splits into two, creating twins that share
all the chromosomes from their mother, but only half from
their father, This is different from identical twins, which come
from one egg and one sperm, and fraternal twins, which
come from two eggs and two sperm. Semi-identical twins
may have different sexes.
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14. WHAT CAUSES TWINS ?
Nobody knows
what causes
identical
(monozygotic)
twins. Everyone
has the same
chance of having
identical twins:
about 1 in 250.
•if patient is pregnant
and over 35 then she is
more likely to have non-
identical twins because
she is more likely to
release more than 1 egg
during ovulation
•non-identical twins run
on the mother's side of
the family, probably
because of an inherited
tendency to release
more than 1 egg
IVF can increase the
chance of twins, as more
than 1 embryo may be
transferred.
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