Second trimester ultrasonography may identify 77 to 97% of fetuses with trisomy 18.

Abstract

n 1984 maternal serum screening for aneuploidy was ushered in when trisomy 18 was identified in a patient in whom the maternal serum AFP level was undetectable. 1 After making this observation, Merkatz and associates examined maternal serum from 41 women who had fetuses with aneuploidy and found that the AFP multiple of the median was lower in fetuses with aneuploidy than in control fetuses. 1 After this observation, numerous investigators reported the association between maternal serum markers and an increased risk for trisomy 21. [2][3][4] Although attention has focused primarily on the detection of trisomy 21, approximately 50% of trisomy 18 fetuses can be identified through maternal serum screening programs. [5][6][7] When women are informed of their increased risk for trisomy 18 after maternal serum screening, many elect to undergo amniocentesis. However, not all atrisk women elect to undergo invasive testing because of the associated risk for pregnancy loss. 8 In 1998 the Genetic Disease Branch of the California Department of Health Sciences screened 353,336 women and identified 1094 who were screen positive for trisomy 18 and eligible for genetic amniocentesis. Of this group, 29.9% (n = 327) declined amniocentesis (personal communication). Abnormal fetal anatomy was present in 97% of fetuses with trisomy 18, with a false-positive rate of 15.7%. Logistic regression identified six markers (choroid plexus cysts, central nervous system malformations, an abnormal nuchal skin fold, ventricular septal defect, outflow tract abnormalities of the heart, and right-to-left chamber disproportion of the heart) and one interaction between markers (right-to-left chamber disproportion and outflow tract abnormalities) to significantly contribute to the identification of 93% of fetuses with trisomy 18, with a false-positive rate of 8.9%. Noncardiovascular markers (choroid plexus cysts, central nervous system malformations, and abnormal nuchal skin fold) identified 77% of fetuses with trisomy 18, with a false-positive rate of 3.9%. Combining rightto-left chamber disproportion of the heart with choroid plexus cysts, central nervous system malformations, and nuchal skin folds identified 83% of fetuses with trisomy 18, with a false-positive rate of 4.4%.

Women's response to fetal choroid plexus cysts detected by prenatal ultrasound

“…[1][2][3][4] Choroid plexus cysts have elicited concern because they are visualized on prenatal ultrasound in fetuses with trisomy 21 and as many as 53% of fetuses with trisomy 18. 5,6 Usually, other abnormal ultrasound findings differentiate these chromosomal aneuploidies from an isolated CPC. [7][8][9] However, several studies have reported that an isolated CPC on prenatal ultrasound may confer a slightly higher risk of trisomy 21 3,10 and 18, 1,11,12 which becomes more significant if additional risk factors, such as advanced maternal age, are present.…”

Sonographic markers of fetal trisomies: second trimester.

“…15 Of these, choroid plexus cysts (Fig. 5) have been the most controversial and the subject of considerable interest.…”

Second-Trimester Sonography and Trisomy 18

“…They are seen in up to half of second-trimester fetuses and are often found with other anomalies. [3][4][5][6][7][8][9][10][11][12][13] In the nearly 2 decades since the initial report by Chudleigh et al, 1 a large volume of literature has been published regarding the sonographic detection of choroid plexus cysts in the second trimester. Despite this, a consensus of opinion has yet to be reached on the genetic significance and appropriate management when these cysts are detected as an isolated finding.…”