Objective: The study's aim was to determine any association between choroid plexus cysts (CPCs) and trisomy 18 in a population of fetuses previously screened by nuchal translucency (NT) thickness measurement.
Methods: During the study period (May 1999 to December 2004), 7,795 fetuses had an NT scan and second-trimester fetal anatomical scan at our institution. The prevalence of trisomy 18 was determined among four types of pregnancies: 1) those with isolated CPCs, 2) those with CPCs and enlarged NT, 3) those with CPCs and other ultrasound markers, and 4) those with CPCs, enlarged NT, and other ultrasound markers. The fetal outcome according to NT and presence of CPCs was calculated. Incidence rates of enlarged NT and CPCs in fetuses with trisomy 18 and fetuses with normal chromosomes were also evaluated.
Results: For the entire population, ten trisomy 18 cases were diagnosed prenatally (prevalence, 0.13%). Among fetuses with enlarged NT, the likelihood ratio of trisomy 18 was significantly increased in fetuses with CPCs compared with fetuses without such cysts (333.6 versus 15.2, P = .002). However, among fetuses with normal NT, no significant difference was demonstrated for likelihood ratio of trisomy 18 between fetuses with and without CPCs.
Conclusion: In pregnancies complicated by isolated CPCs, fetal karyotyping is not indicated when no additional anomaly is detected on ultrasonographic examination and first-trimester NT results are normal.