Prenatal Screening

Prenatal Screening

Kathryn J. Shaw (Maternal-Fetal Medicine, White Memorial Medical Center, Los Angeles) gives expert video advice on: What is "prenatal screening"?; What is the prenatal triple-marker test?; What are "neural tube defects"? and more...

What is "prenatal screening"?

Prenatal screening identifies if the woman is at risk for delivering a child with down syndrome, a child with a neural tube defect, also know as spinal defects, or Spina Bifida. Prenatal screening programs also are able to identify if the mother is at risk for delivering a child with a syndrome referred to as Trisomy 18, or another syndrome know as Smith-Lemley-Opitz syndrome.

What is the prenatal triple-marker test?

The pre-natal triple-marker screen refers to a blood test that is offered to the pregnant woman between 15 and 20 weeks. The "triple" refers to three hormones that are measured in the mother's bloodstream, and depending on the pattern, or the level of those hormones, a risk assessment is made to determine if she is at risk of having a child with Down Syndrome, Spina Bifida (also known as neural tube defects), Trisomy 18, or the SLOS Syndrome.

What are "neural tube defects"?

Neural tube defects, also referred to as spina bifida or spinal defects, are a group of abnormalities involving malformations along the fetus' head or spine. This disorder was actually the original reason why genetic screening was started. The incidence is about 1 in 2000. They can be mild with a small defect in the spine and limited impact on the child's ability to walk. The more extreme example would be something referred to anencephaly, which is a failure of the skull to develop. Those childs will either die in utero or in the delivery or shortly after birth.

What is "Down syndrome"?

Down syndrome is a common birth defect that is due to an extra chromosome number 21. The normal number of chromosomes in all human cells is 46. This is 23 pairs of chromosomes numbered 1 to 23. Down syndrome is either an entire extra 21 or an extra piece of chromosome number 21. The infants affected with Down syndrome have a characteristic facial appearance that most of us would recognize. It involves changes in the eye shape with downward slanted eyes. Often they're described as almond-shaped eyes. These children with Down syndrome will all have some degree of mental retardation, although it's variable. Individuals with Down syndrome also have an increased chance of having birth defects involving the heart. They also are at risk for other childhood illnesses, including leukemia and other problems with their immune system.

What is "trisomy 18"?

Trisomy 18 is another syndrome. It's extremely rare: the reported incidence is approximately one in 10,000. Trisomy 18 is a syndrome whereby the affected individual has an extra chromosome number 18. Instead of having two of number 18, there are three. This syndrome, again, is associated with profound mental retardation and growth restriction. The affected fetus often dies in utero prior to delivery, and it is uniformly not compatible with survival. All infants affected by Trisomy 18 either die during the pregnancy, or shortly thereafter birth. Again, this is something that can be identified in terms of the mother's risks with the triple marker screen.

What is "smith-lemli-opitz syndrome" or "SLOS"?

SLOS stands for "Smith-Lemli-Opitz syndrome". SLOS is a very rare disorder that involves biochemical abnormality in the developing foetus or the affected individual. It is associated with profound growth restriction during the foetal time period and also profound mental retardation in the affected infant and child. SLOS is also associated with a marked reduction in life expectancy, and most individuals that are affected will die in the childhood period.