Ultrasonographic diagnosis of trisomy 18: is it practical in the early second trimester?

The objective of this paper was to determine the rate of prenatal detection of ultrasonographic abnormalities in fetuses with trisomy 18 during the early second trimester. Our prenatal diagnosis database (encompassing January 1987 to June 1996) was searched for all patients referred for prenatal genetic evaluation between 14 and 22 weeks of gestation and who were found to have a fetus with a trisomy 18 karyotype. The sonographic reports and films were evaluated for the presence or absence of fetal anatomic abnormalities. Thirty-five fetuses were identified with a mean age of 17.3+/-2.0 (standard deviation) weeks. Thirty of the 35 (86%) had at least one detected abnormality. Most fetuses had more than one abnormality, with the mean number of abnormalities per fetus being three (range, 0 to 6). The most common abnormalities noted were persistent abnormal position of fetal fingers (89%); choroid plexus cysts (43%); abnormally shaped fetal head (strawberry or lemon) (43%); two-vessel umbilical cord (40%); cardiac defects (37%); intrauterine growth restriction (29%); omphalocele (20%); neural tube defects (9%); and cystic hygroma or lymphangiectasia (14%). Abnormalities of amniotic fluid volume (12%) and renal defects (9%) were seen less frequently. These data suggest that in the early second trimester, the time of most routine screening ultrasonographic examinations, most but not all fetuses with trisomy 18 have sonographically detectable anatomic abnormalities. The fetal hand appears to be abnormal in most early second trimester fetuses with trisomy 18, but the abnormality may be subtle and or unilateral.