Down's syndrome screening in women under 35 with maternal serum hCG

Article Abstract:

Down's syndrome is a chromosomal abnormality marked by mental retardation and other congenital malformations. Although the risk for Down's syndrome increases with advanced maternal age, 80 percent of the Down's syndrome infants are born to women who are under 35 years of age. Down's syndrome can be detected when the cells obtained during amniocentesis are analyzed. It is current obstetrical practice to recommend amniocentesis to all women over 35. In women under 35, the risk for a Down's syndrome fetus is determined by measuring the amount of alpha-fetoprotein (AFP) detected in the mother's blood and factoring in the mother's age. However, even when amniocentesis is performed on all women with a positive maternal AFP test, only 25 percent of the Down's syndrome pregnancies in this age group will be detected. In an effort to improve detection of Down's syndrome in the under-35 age group, investigators found that the amount of human chorionic gonadotropin hormone (hCG), the hormone produced by the developing embryo and placenta, is higher in pregnancies complicated by Down's syndrome. To see if measuring the hCG levels in women under 35 improves the diagnosis of Down's syndrome, two screening methods were compared. The hCG and maternal AFP were measured in blood frozen during pregnancy taken from 16 women under 35 years of age who gave birth to a Down's syndrome child, and from 614 women with normal pregnancies. When maternal age and maternal AFP levels were used to screen for Down's syndrome, four out of the 16 pregnancies complicated with Down's were correctly identified (25 percent). When the level of hCG was added to the screening protocol, 10 out of the 16 Down's syndrome pregnancies were correctly identified (62.5 percent). The diagnosis of Down's syndrome in women under 35 years of age was greatly improved when hCG measurements were used in conjunction with AFP analysis and maternal age, although over a third of the cases of Down's syndrome infants were still not detected by this technique. (Consumer Summary produced by Reliance Medical Information, Inc.)

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Maternal serum screening for aneuploid pregnancy by alpha-fetoprotein, hCG, and unconjugated estriol

Article Abstract:

While pregnant women 35 or older are offered prenatal diagnostic testing to detect abnormal fetal karyotypes (chromosome number and appearance), testing is also recommended for younger women when they are considered at risk for an abnormal number of fetal chromosomes (aneuploidy). Since termination of pregnancy, if desired, is best performed as early as possible, tests that provide this information early in gestation are highly desirable. In addition, noninvasive tests are preferable to invasive ones, if the results are reliable. It is possible that a combination of three blood tests, all currently used in prenatal diagnosis, could be valuable in identifying pregnant women under 35 who should undergo amniocentesis (sampling of amniotic fluid for fetal cells). This was tested by assaying stored blood samples from women with known pregnancy outcomes. The markers of interest were maternal serum alpha-fetoprotein (MSAFP), human chorionic gonadotropin (hCG), and unconjugated estriol (E3). Thirty-four women had fetal aneuploidy; a control group consisted of 85 women with normal pregnancies who underwent amniocentesis because of advanced maternal age. Results showed that this three-hormone assay was a good predictor of trisomy 21 (Down syndrome), which was predicted in 63 percent of the cases, but was falsely predicted in 5 percent. However, other aneuploidies were not well detected by these tests. In general, the test results did not lead to identifying all of the women who needed amniocentesis. A discussion is presented of the limitations of the three-hormone assay, particularly in the US medical environment, where informed consent may be difficult to obtain. Women should understand that this approach cannot substitute for an invasive test (such as amniocentesis) in the information it provides. (Consumer Summary produced by Reliance Medical Information, Inc.)

Birth defects, Aneuploidy

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Maternal serum unconjugated oestriol and human chorionic gonadotrophin levels in twin pregnancies: implications for screening for Down's syndrome

Article Abstract:

Down syndrome is a congenital disorder characterized by moderate to severe mental retardation, and distinct physical features including a sloping forehead, small ear canals, wide-set eyes, short broad hands with a single crease in the palm, a flat or absent nose bridge, low-set ears, and a dwarf-like build. This disorder can be diagnosed prenatally, or before birth, by measurement of maternal blood levels of estriol, alphafetoprotein (AFP), and human chorionic gonadotrophin (hCG) in the second trimester, or second three months of pregnancy. AFP levels in twin pregnancies are twice those in singleton, or single fetus pregnancies. Estriol and hCG levels may also be elevated in twin pregnancies. The blood levels of estriol, hCG, and AFP were measured in 200 women with twin pregnancies and 600 women with singleton pregnancies. The blood levels of estriol, hCG, and AFP in twin pregnancies were 1.67, 1.84, and 2.13 times those of singleton pregnancies. These findings confirm results of previous studies showing AFP levels in twin pregnancies to be double those of singleton pregnancies. The risk of Down's syndrome in twin pregnancies can be estimated by adjusting values of estriol, hCG, and AFP to corresponding values in singleton pregnancies. However, the rate of detection of Down syndrome in twin pregnancies may be less than that of singleton pregnancies, because an unaffected twin will tend to normalize the elevated values of these factors. (Consumer Summary produced by Reliance Medical Information, Inc.)

Physiological aspects, Twins

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