The prevalence of IUGR in fetuses with trisomy 18 increases with gestational
age.
- First trimester IUGR has been
reported, but its prevalence is unknown as the numbers of cases are too
few.
- Second trimester IUGR - 28%
of fetuses.
- Third trimester IUGR - 87% of
fetuses (1-2).
The cycle time for cell growth and division is longer for
trisomic cells than for cells with a normal karyotype. The slower rate of cell
growth explains the growth restriction detected on antenatal sonography (3).
The survival rate for trisomy 18 fetuses that have a normal diploid cell
line in their placenta is better than those fetuses that have a mosaic trisomy
18 placenta.
Trisomy 18 fetuses with a nonmosaic trisomy 18 placenta always result in an
embryonic or fetal demise (4).
Link
to Ultrasound in the Diagnosis of IUGR
- Nyberg DA, Kramer D, Resta RG
et.al. Prenatal sonographic findings of trisomy 18: review of 47 cases. J Ultrasound
Med 1993;2:103-113.
- Kuhn P, de Lourdes Brizot M,
Pandya PP et.al. Crown-rump length in chromosomally abnormal fetuses at
10-13 weeks gestation Am J Obstet Gynecol 1995;172:32-35.
- Paton GR, Silveo MF, Allison
AC. Comparison of cell cycle time in normal and trisomic fetuses.
Humangenetik 1974;23:173-182.
- Kalousek DK, Barrett IJ,
McGillvray BC. Placental mosaicism and intrauterine survival of trisomies
13 and 18. Am J Hun Genet 1989;44:338-343.