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Alternatives To Genetic Amniocentesis

Friday, March 16, 2012 - 14:05

Amniocentesis is highly accurate, but expectant parents must wait until at least the 15th week of pregnancy, and it does involve some risks. There are some other tests available that can either be done earlier or are less invasive.

Chorionic Villus Sampling (CVS)

Chorionic Villus Sampling (CVS) is an alternative to amniocentesis that can be performed between 10 and 12 weeks of pregnancy. As with amniocentesis, ultrasound is used to determine the position of the baby. Once that has been established, the doctor or technician will then remove a tiny sample of the placenta, either through the cervix (the neck of the womb) or through a small needle inserted into the abdomen.

Like amniocentesis, CVS can detect chromosomal abnormalities, but it does not detect neural tube defects (although these can sometimes be detected with an ultrasound). It carries a slightly higher risk of miscarriage than amniocentesis (one in 100 to one in 200), but it can be performed earlier in the pregnancy, allowing for the possibility of ending the pregnancy in the first trimester.

Multiple Marker Screening

The multiple maternal marker screening, also known as the triple screen or the quadruple screen, is a blood test given between 15 and 20 weeks of pregnancy. It tests for three or four substances in the blood whose presence can indicate a risk of certain birth defects:

  • Alpha-fetoprotein (AFP): A high AFP signifies the risk of neural tube defects, such as spina bifida, or abdominal wall defects. A low AFP is associated with Down syndrome.
  • Human chorionic gonadotropin (hCG): High hCG is associated with Down syndrome.
  • Unconjugated estriol (uE3): Low estriol may indicate Down syndrome. Low levels of all three hormones indicate a risk for trisomy 18, also known as Edward's syndrome.
  • Inhibin A (inhibin) if it's a quadruple screen: The detection rate for Down syndrome increases with inhibin screening.

The multiple marker test may also indicate risk of pregnancy complications such as pre-eclampsia, premature birth, or miscarriage.

Remember that the multiple marker test is a screening test used to help a woman understand the risk of her baby suffering from certain conditions. It should be used to help determine if further tests, such as amniocentesis, are necessary.

Ultrasound Studies

There are many markers on a fetus, such as neck skin thickness or anomaly, that can raise the suspicion of a chromosomal abnormality. These markers, which can be detected through ultrasound, may help determine the need for amniocentesis.

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