Prenatal diagnosis

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(Redirected from Prenatal testing)

Prenatal diagnosis is the diagnosis of disease or condition in a fetus or embryo before it is born. The aim is to detect birth defects such as neural tube problems, chromosomal abnormalities and other conditions to prepare the parents for the birth. Genetic counseling often accompanies prenatal diagnosis.

There are both invasive and non-invasive methods of diagnosing a problem before birth. Examination of the mother's belly and ultrasonography are routinely done to check for any abnormality in the pregnancy.

If an abnormality is detected by a non-invasive procedure, a more invasive technique may need to be used. Invasive techniques include amniocentesis, which can be done from about 14 weeks gestation, and usually up to about 20 weeks, and chorionic villus sampling which can be done earlier (between 9.5 and 12.5 weeks) but is slightly more risky to the unborn child.


Reasons for prenatal diagnosis

Knowing a fetus is abnormal before birth allows parents to plan for any health needs of their baby in advance of it being born. It can also prepare them for the birth, enabling them to receive counselling before birth, reducing the shock and other reactions when the baby is born. As well as this, it gives the option of abortion of the fetus.

Healthcare staff can also prepare for the delivery, and have suitable treatment ready for when the baby is born.

The type of prenatal diagnosis done depends on the situation of the parents. In an older mother (for instance over 35), or a parent with a inheritable genetic condition, a more invasive technique may need to be done. This can detect chromosomal abnormalities (such as Down's syndrome) which are more common in older mothers, or the specific genetic problem a parent may have. Genetic counseling is often offered to help parents decide what type of testing is right for their situation.

Risk Factors Qualifying a Woman for Prenatal Testing

-Pregnant women over the age of 35 -Women who have previously had premature babies or babies with a birth defect, especially heart or genetic problems -Women who have high blood pressure, lupus, diabetes, asthma, or seizure disorder -Women whose partners have ethnic backgrounds prone to genetic disorders or mental retardation

Ethical and practical issues

Ethical Issues of Prenatal Testing -Abortion is the main option for many post-prenatal testing results. -People can pick and choose what children they would like to have. This could lead to choice in sex, physical characteristics, and personality in children. -Are mentally or physically abnormal children less valuable in our society? -How do we draw the line for prenatal testing and the options and information parents are given? -Are women really making decisions based on what they want? -How are parents supposed to choose when faced with the option of aborting their child?

Will the result of the test affect treatment of the fetus?

In some genetic conditions, for instance cystic fibrosis, an abnormality can only be detected if DNA is obtained from the baby. Usually an invasive method is needed to do this.

If a genetic disease is detected, there is often no treatment that can help the fetus until it is born. It does give parents the option to consider abortion of the baby.

If abortion isn't an option for a particular couple (because of their own beliefs), invasive prenatal diagnosis of such a condition is unhelpful as the test puts the child at risk, and knowing the result doesn't help the child. Genetic counseling can help families make informed decisions regarding results of prenatal diagnosis.

False positives and false negatives

Ultrasound of an unborn baby can often miss subtle abnormalities. Similarly a fetus may look to be abnormal by ultrasound, but may be born completely healthy.

Genetic testing, while it has fewer false positives, will often not detect every form of the disease.

Both false positives and false negatives will have a large impact to a couple when they are told the result, or when the child is born. Genetic counseling can help families make informed decisions regarding results of prenatal tests.

Societal Pressures on Prenatal Testing Decisions Amniocentesis has become routine in prenatal care visits for women who are “at risk” or over a certain age. All obstetricians have most patients undergo the triple test, HIV test and ultrasounds routinely. Just like the saying, “hands get washed when they are dirty; amnio gets done when you are over thirty-five.” Furthermore, amnio gets performed because of medical encouragement. Doctors often advise women to have these test performed, and women listen because they have this trust factor in their doctors. Also, in most cases there is social support from husbands, who also tend to encourage prenatal test. If women who are “at risk” chose not to have any tests performed, they often have to justify themselves since they are going against the norm that has been set by society. The main argument on not to have amnio is the Right-to-life argument. Everybody has the right to live. Right-to-life activists believe that “because in utero treatment is in its infancy, prenatal diagnosis today is used to seek out and destroy ‘defective’ infants. It is important to remember that many couples face hard decisions whether to have or not to have prenatal testing, such as amniocentesis, done because of the many social and economical implications that surround it.

Methods of prenatal diagnosis

Relatively non-invasive methods: (to the baby)

  • Examination of the mother's uterus from outside the body. (i.e. Feeling the mother's 'stomach'.)
  • Ultrasound detection - Commonly used to check the baby's sex, to look for twins, and also to check for any abnormal development.
  • AFP screening can check levels of alpha fetoprotein, β-hCG, and estriol in the mother's serum.
  • Detection of fetal blood cells in maternal blood. With this technique it is technically possible to obtain a sample of the baby's DNA using blood cells from the fetus, that have made their way into the mother's bloodstream.

More invasive methods:

  • Chorionic villus sampling - Involves getting a sample of the chorionic villus and testing it. This can be done earlier than amniocentesis, but is a more risky procedure.
  • Amniocentesis - This can be done once enough amniotic fluid has developed to sample. Cells from the baby will be floating in this fluid, and can be separated and tested.
  • Embroscopy and fetoscopy - These involve putting a probe into a women's uterus to observe (with a video camera), or to sample blood or tissue from the baby.

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