Prenatal Health Dictionary

Prenatal screening of fetal abnormalities may be the result of screening tests carried out on most or all pregnant women, or as the result of speci?c diagnostic tests performed to detect speci?c conditions. Prenatal diagnosis is important as it will identify babies who might need medical or surgical treatment before or soon after birth. In addition, it may also detect severe abnormalities for which parents might decide to have a therapeutic ABORTION.

ULTRASOUND scanning is probably the most widely used diagnostic tool in obstetric practice. It can detect structural abnormalities such as SPINA BIFIDA and CLEFT PALATE and even cardiac and renal problems. A series of scans can assess whether the baby is growing at a normal rate; ultrasound may also be used to assist with other diagnostic tests (e.g. AMNIOCENTESIS – see below).

Tests on the mother’s blood can also diagnose fetal abnormalities. Alphafetoprotein (AFP) is produced by babies and ‘leaks’ into the AMNIOTIC FLUID and is absorbed by the mother. In spina bi?da and other neural-tube defects there is increased leakage of AFP, and a blood test at 16 weeks’ gestation can detect a raised level which suggests the presence of these abnormalities.

The triple test, also performed at 16 weeks, measures AFP and two hormones – HUMAN CHORIONIC GONADOTROPHIN and unconjugated OESTRADIOL – and is used in diagnosing DOWN’S (DOWN) SYNDROME.

Amniocentesis involves inserting a needle through the mother’s abdominal wall into the uterus to remove a sample of amniotic ?uid at 16–18 weeks. Examination of the ?uid and the cells it contains is used in the diagnosis of Down’s syndrome and other inherited disorders. The test carries a small risk of miscarriage.

Chorionic villus sampling may be used to diagnose various inherited conditions. A small amount of tissue from the developing PLACENTA is removed for analysis: this test has the advantages of having a lower incidence of miscarriage than amniocentesis and is carried out at an earlier stage (9–13 weeks).

Analysis of a blood sample removed from the umbilical cord (cordocentesis) may diagnose infections in the uterus, blood disorders or inherited conditions.

Direct observation of the fetus via a viewing instrument called a fetoscope is also used diagnostically and will detect structural abnormalities.

Most tests have a recognised incidence of false positive and negative results and are therefore usually cross-checked with another test. Counselling of the parents about prenatal tests is important. This allows them to make an informed choice which may not necessarily involve terminating the pregnancy if an abnormality is found. (See PREGNANCY AND LABOUR.)... prenatal screening or diagnosis

(NIPD) see prenatal diagnosis.... noninvasive prenatal diagnosis

(antenatal diagnosis) diagnostic procedures carried out on pregnant women in order to detect the presence of genetic or other abnormalities in the developing fetus. Ultrasound scanning (see ultrasonography) remains the cornerstone of prenatal diagnosis. Other procedures include chromosome and enzyme analysis of fetal cells obtained by *amniocentesis or, at an earlier stage of pregnancy, by *chorionic villus sampling (CVS). Noninvasive prenatal diagnosis involves a blood test to analyse cell-free fetal DNA in maternal blood. It can be performed during the first trimester and is used for fetal rhesus (Rh) determination in Rh-negative mothers, fetal sex determination in pregnancies at risk of sex-linked disorders, and for some single-sex gene disorders (e.g. achondroplasia). Compare prenatal screening.... prenatal diagnosis

*screening tests carried out to estimate the risk of chromosomal or other abnormalities being present in a developing fetus. They include blood tests to measure levels of *human chorionic gonadotrophin (hCG), *PAPP-A, *alpha-fetoprotein (AFP), inhibin (see activin), and *unconjugated oestriol (uE3) (see also triple test) and also ultrasound scanning for the presence of soft markers (see ultrasound marker; nuchal translucency scanning). If the results indicate a high risk of abnormalities being present, a diagnosis may be confirmed by more invasive procedures (see prenatal diagnosis).... prenatal screening