Sensitivity and specificity of screening for Down syndrome with alpha-fetoprotein, hCG, unconjugated estriol, and maternal age

Article Abstract:

Alpha-fetoprotein is an antigen, or a substance capable of provoking an immune response, that is present in the human fetus and in the adult under certain abnormal conditions. The blood levels of alpha-fetoprotein can be measured in the pregnant woman to detect fetal abnormalities, and this test is referred to as maternal serum alpha-fetoprotein (MSAFP) screening. This test is both highly sensitive and specific for detecting open neural tube defects, and can identify about 80 to 90 percent of cases of open spina bifida and anencephaly, which are defects of the fetal spinal cord and brain. MSAFP screening is less effective in detecting Down syndrome, particularly in younger women. Other studies suggest that Down syndrome may be more effectively detected by measurement of human chorionic gonadotropin (hCG), a gonad-stimulating hormone produced by the placenta, and unconjugated estriol (uE3), a type of estrogen. Pregnant women in the United States 35 years and older are offered screening for Down syndrome and other chromosomal abnormalities. The sensitivity and specificity of maternal serum screening for Down syndrome were assessed using different combinations of MSAFP, hCG, and uE3 in 54 confirmed Down syndrome pregnancies and 657 normal pregnancies. The detection rate was two to three times greater with MSAFP, hCG, and uE3 than with MSAFP alone. The detection rate for Down syndrome using all three markers increased from 50 to 77 percent with increasing age of the mother, and was 60 percent in a representative population. Omission of uE3 resulted in a decrease of the detection rate to 48 percent. In a screening of 1,000 women, the false-positive rate was similar for all three markers and MSAFP alone. The positive predictive value for Down syndrome using all three markers was 2.2 percent and increased to 5.9 percent in older women. Hence, the addition of uE3 and hCG to the screening process increased the positive-predictive value by 50 to 300 percent, in relation to maternal age. Thus, the effectiveness of screening for Down syndrome is increased by screening for all three markers, MSAFP, hCG, and uE3. (Consumer Summary produced by Reliance Medical Information, Inc.)

Evaluation, Measurement, Testing, Medical screening, Health screening, Down syndrome, Chorionic gonadotropin, Chorionic gonadotropins, Estradiol

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Prenatal findings in Brachmann-de Lange syndrome

Article Abstract:

A report is presented of a case of Brachmann-de Lange syndrome, a congenital disorder involving mental retardation, small size, a small and abnormally shaped head, and a characteristic facial type. Prenatal tests at 19 weeks' gestation showed a low level of maternal serum alpha-fetoprotein (MSAFP). (Levels of this fetal protein can be detected in maternal blood.) Subsequent ultrasound examination revealed structural abnormalities. The fetal karyotype (chromosomal) analysis was normal. The infant was born via cesarean section after almost 36 weeks' gestation, when it was found to have several abnormalities, including a heart defect, and was diagnosed with Brachmann-de Lange syndrome. It died at the age of 10 days. This syndrome may be present in as many as 1 out of every 30,000 births, but no definitive prenatal diagnostic method for the condition has been developed. MSAFP determination and ultrasound evaluation can help to make the diagnosis; these tests are readily available to pregnant women. (Consumer Summary produced by Reliance Medical Information, Inc.)

Methods, Case studies, Diagnosis, Birth defects, Prenatal diagnosis

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