Explanation

All patients presenting for prenatal care should be offered prenatal genetic screening. Quadruple marker tests are performed in the early second trimester. They consist of measurement of alpha-fetoprotein (AFP), unconjugated estriol (E3), human chorionic gonadotropin (hCG), and inhibin A (INH A). Quadruple marker tests have different patterns in certain genetic anomalies. That of trisomy 18 includes low human chorionic, gonadotropin, estriol levels, alpha-fetoprotein, and inhibin A levels. Trisomy 18 is the second most common autosomal trisomy detected in the second trimester, after trisomy 21. It is lethal in early childhood. Characteristic ultrasonographic findings include limb abnormalities such as upper limb reduction, clenched hands with overlapping index finger, clubbed feet, and rocker bottom feet. Nuchal thickening and cystic hygroma are typically present, with facial defects such as clefts, micrognathia, low-set ears, and microphthalmos.

Sex chromosome aneuploidy (A) (i.e., 47 XXX and 47 XYY), and trisomy 13 (B) are associated with normal quad screen measures. Trisomy 21 (D) is characterized by elevated human chorionic gonadotropin and inhibin A levels in addition to decreased estriol and alpha-fetoprotein levels.