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Identical twins (monozygotic twins)
Two offspring created when a single fertilized egg
divides to form two separate embryos during the
first 2 weeks after conception. Identical twins account for about 30% of
naturally occurring twins in the United States.
Implantation (nidation)
Penetration into the uterine
mucosa by the embryo. Implantation occurs approximately 6 days after conception.
Abnormal implantation of the embryo outside of the uterus is called an ectopic
pregnancy.
Incompetent Cervix
See cervical incompetence
Induction of labor
Stimulation of uterine contractions before the spontaneous onset of labor in order to achieve a vaginal delivery.
ACOG Practice Bulletin No. 10: Induction of Labor .American College of Obstetricians and Gynecologists.1999
Infant
A child under one year of age.
Infertility
Inability to conceive after one full year of
regular sexual intercourse without the use of contraception.
Intrauterine fetal death
A fetus with a crown-rump length more than 15 mm long without cardiac
activity.
In utero
Inside the uterus (womb).
Inversion
A chromosomal rearrangement in which a segment of the chromosome
breaks away from the chromosome and re-inserts into the chromosome 180 degrees
relative to its previous orientation.
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Pericentric inversion
An inversion in which
the breakpoints occur on both arms of a chromosome. The inverted segment
includes the centromere
(
the constricted portion of the chromosome).
Inversion of chromosome 3 or 8 has been associated with an increased
risk for abnormal offspring . Pericentric inversion of chromosome 9 appears to be a normal
variant in humans, and occurs in approximately one percent of the
population. Inversion of chromosome 9 does not appear to
be associated with an increased risk of miscarriage or abnormal offspring.
46,X,inv (Y)(p11.2q11.2)
Pericentric inversion of the y chromosome is usually a familial variant
of no known clinical significance occurring in 1 in 1000 males. A
chromosome analysis of the father's blood may be performed to
determine if this Y chromosome is inherited ( 5 mL in a green top sodium
heparin tube).
REFERENCES
Milunsky JM In Milunsky, A ed , Genetic Disorders of the Fetus, 5th
edition Baltimore: The Johns Hopkins University Press 2004. P 322
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Paracentric inversion
An inversion in which
the breakpoints occur on one arm of a chromosome.
The inverted segment does NOT include the centromere
(
the constricted portion of the chromosome).
Because paracentric inversions do not change the arm ratio of the
chromosome they are difficult to detect on routine chromosome analysis.
The risk of
abnormal children for persons who have a paracentric inversion on one
chromosome is
low but increases with the finding of recurrent abortions or
abnormal children or both in other carriers in the family. |
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Isochromosome
A chromosome with two identical arms
due to abnormal division of the chromosome in the transverse plane instead of longitudinally.
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