Couldn't find what you looking for?

TRY OUR SEARCH!

Prenatal screening and diagnosis

by — Last updated: 2022-04-14 in Women's Health

Table of Contents

Down syndrome is a condition in which extra genetic material causes delays in the way a child develops, and often leads to learning difficulties. It affects 1 in every 800 babies born.

A new study supports screening for Down syndrome in earlier weeks of pregnancy than what has traditionally been recommended. These are very good, easy to do and effective prenatal diagnostic tools that can help in detecting abnormalities characteristic to Down syndrome!

Maternal serum screening

The proven fact is that this maternal serum screening allows the detection of trisomy 21 pregnancies in women in younger than 35 years who give birth to about 70 percent of infants with Down syndrome.
The serum markers most widely used are:
  • Alfa-fetoprotein
  • Unconjugated estriol
  • Human chorionic Gonadotropin
That’s why - this combination is known as "triple test"! The test is usually performed at 15 to 18 weeks of pregnancy. The chances of trisomy 21 is calculated on the basis of each of the serum marker results and the patient’s age.
 
Results - The triple test can detect 60 percent of trisomy 21 pregnancies. Young mothers also must understand that a normal result reduces the likelihood of trisomy 21 but does not exclude it.
 
There are several factors that have influence on test. The factors are:
  • Gestational age
  • Maternal weight
  • Maternal race
  • Maternal insulin-dependant diabetes
  • Multiple fetal pregnancy
  • Family history of Down syndrome
Test results also can help a woman manage her pregnancy more effectively.

Ultrasound assessment

It is proven that ultrasound test improves the performance of the triple test. This test uses sound waves to take a picture of the fetus. Ultrasound can help determine the gestational age of the fetus and show if a woman is carrying twins.
A Simple Ultrasonographic test can detect many abnormalities associated with fetal Down syndrome. Some of the common findings are:
  • Increased nuchal fold thickness >5 mm
  • Intrauterine growth restriction
  • Flat facies
  • Small ears
  • Choroids plexus cysts
  • Congenital heart defects
  • Renal pelvis dilation
  • Shortened humerus and femur
  • Increased iliac wing angle
  • Incurving of the fifth finger
  • Increased space between first and second toes
  • Two-vessel umbilical cord
If the ultrasound does not provide an explanation for an abnormal test result, additional diagnostic testing is recommended.

Chorionic villus sampling

Women who receive abnormal results on other screening test may be offered a prenatal test called chorionic villus sampling, which is done between 10 and 12 weeks of pregnancy. Chorionic villus sampling is one very good and effective prenatal test used to identify various genetic problems, including Down syndrome. Using a thin tube guided through the mother’s cervix or a needle inserted into your uterus, doctor takes a sample of chorionic villi from the placenta.
 
What's so good about this diagnostic tool? Chorionic villus sampling can provide genetic information about your baby earlier in your pregnancy than can other diagnostic tests, such as amniocentesis. The test might be offered if your baby has an increased risk of a specific chromosomal or genetic disorder. On the other hand - chorionic villus sampling cannot detect neural tube defects, such as spina bifida.

Amniocentesis

Amniocentesis is a prenatal test used to identify various genetic problems. It is done by using a thin needle which is inserted into the uterus by doctor! Then, the doctor withdraws a sample of the amniotic fluid that surrounds and protects the baby. This fluid contains fetal cells and various chemicals produced by the baby. With genetic amniocentesis, the chromosomes and genes in these cells or the chemicals in the amniotic fluid can be tested for certain abnormalities, such as Down syndrome and spina bifida. What's also good? With maturity amniocentesis, the amniotic fluid could be also tested to determine whether a baby's lungs are mature enough for birth.

Indications for an amniocentesis include:
  • A chromosomal abnormality or neural tube defect in a previous pregnancy
  • Abnormal results from a prenatal screening test, such as first trimester screening or the quad marker screen
  • A family history of central nervous system defects, Down syndrome or other genetic disorders
One problem with amniocentesis is that it carries various risks, including:
  • Miscarriage.
  • Rupture of the amniotic sac
  • Cramping
  • Light vaginal bleeding.
  • Rh sensitization
  • Needle injury
  • Neonatal respiratory distress syndrome
  • Neonatal pneumonia
  • Limb reduction defects
  • Bleeding

These risks are small, and the pros and cons should be discussed with the doctor before having the test.