Book of Medical Disorders in Pregnancy - Tintash

in meiosis are more likely, and result in
trisomies. The table below indicates the
relative risk of having a baby with
various trisomies based upon maternal
age: Listed below are some of the more
common chromosomal abnormalities
that can occur. The descriptions are for
the completely abnormal condition in
which all fetal cells contain the abnormal
karyotype. Bear in mind that "mosaicism"
can occur. A "mosaic" is a person
with a combination of two cell lines with
different karyotype (normal and abnormal).
When karyotyping is performed,
multiple cells are analyzed to rule out
this possibility.
Maternal
Age
Trisomy
21
Trisomy
18
Trisomy
13
15 – 19 1:1600 1:17000 1:33000
20 – 24 1:1400 1:14000 1:25000
25 – 29 1:1100 1:11000 1:20000
30 – 34 1:700 1:7100 1:14000
35 – 39 1:240 1:2400 1:4800
40 – 44 1:70 1:700 1:1600
45 – 49 1:20 1:650 1:1500
An example would be a Turner's mosaic,
with a 45, X/46, XX karyotype, with
some cells having the abnormal karyotype
and some cells having a normal
karyotype. The mosaic condition is not
as severe as the completely abnormal
karyotype, and the features may not be
as marked, and live births may be
possible. Sometimes the mosaicism is
confined to the placenta ("confined
placental mosaicism"). A placenta with
an abnormal karyotype (confined
placental mosaicism) may lead to
200
stillbirth, even though the fetus has a
normal karyotype; conversely, a placenta
with a normal karyotype may allow
longer survival for a fetus with a
chromosomal abnormality. Rarely, a
translocation of part of one chromosome
to another in the parent will be passed on
to the child as a partial trisomy (such as
6p+ or 16p+) which may not be as
severe as a complete trisomy. Trisomy
21: Down syndrome; incidence based
upon maternal age, though translocation
type is familial; features can include:
epicanthal folds, simian crease,
brachycephaly, cardiac defects. Trisomy
21 (47, XY, +21) karyotype, diagram
Trisomy 21, facial features, gross,
Trisomy 21, abnormal creases, hands,
gross, Trisomy syndrome, cystic
Hassall's corpuscles in thymus, medium
power microscopic and trisomy 18:
Features include micrognathia,
overlapping fingers, horseshoe kidney,
rocker bottom feet, cardiac defects,
diaphragmatic hernia, omphalocele.
Trisomy 18 (47, XY, +18) karyotype,
diagram, Clenched hand with trisomy 18,
gross and diaphragmatic hernia, gross.
Trisomy 13: Features include
microcephaly, cleft lip and/or palate,
polydactyly, cardiac defects, holoprosencephaly.
Trisomy 18 (47, XY, +18)
karyotype, diagram, Trisomy 18, facial
features, gross, Clenched hand with
trisomy 18, gross and diaphragmatic
hernia, gross. Trisomy 16: Seen in abort
uses from first trimester. Never liveborn.
Trisomy 16 karyotype, diagram. Monosomy
X: Turner's syndrome; can
survive to adulthood; features include
short stature, cystic hygroma of neck
(leading to webbing), infertility,
coarctation. Monosomy X, or Turner's
syndrome (45, X) karyotype, diagram,
Monosomy X, or Turner's syndrome,
streak ovaries in adult, gross, Massive