Tests for the detection of congenital anomalies

The development of methods to measure levels of alpha fetoprotein (AFP) in maternal blood during pregnancy, has had a significant effect on the prenatal detection of certain fetal abnormalities. A maternal blood level of AFP high indicating that the fetus has an increased risk of neural tube defects (meningocele, spina bifida), whereas a low level of AFP can be associated with increased risk of Down syndrome or other abnormalities chromosome. The importance of the development of identification evidence of congenital abnormalities is underlined by the fact that 90% of the medullary canal defects occur in the absence of positive family history and that 80% of cases of Down syndrome occurs in women under 35 years of age.

Following the recognition of the AFP and valuable method of investigation, it has attempted to identify additional markers that when join AFP levels could improve their predictive accuracy. Currently used as markers two hormones chorionic gonadotropin (HCG) and 17 B estradiol. All these as non-invasive methods. In pregnancies affected by Down syndrome, the hCG level is above normal, while AFP levels are below normal.

The three values together with maternal age are used to calculate the specific risk to the patient during the second trimester for Down syndrome. The best time to perform the scan is between 15th and 18th weeks of gestation, 15 weeks before samples are useless for interpretation. Therefore the confirmation of gestational age by ultrasound is of vital importance.

In addition to these tests is the study of amniotic fluid, both the quantification of AFP, as acetylcholinesterase or karyotype which is final and conclusive.

 

 

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