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Genetics 101 - Screens and Testing

PostPosted: Dec 02, 2006 12:19 pm
by Jenny
Genetics 101

What are Chromosomes? ... echrom.cfm

Super basically, Chromosomes are the instructions our bodies have from the original joining of sperm and egg on how to create a person. They are the map for every trait that person will have from eye color to body type.

Why should I be concerned about Chromosomes? What is a Trisomy? ... peinfo.cfm

If conception occurs and the baby has too many or too few of even one chromosome, then the instructions for building the human are off. Imagine trying to build a clock, and you have two page fours that are different from each other. One says to use roman numerals and the other says to use numbers. Your kit came with both. You try to put both on the face of the clock, but then there isn’t room for everything to work properly so you get around the face of the clock, and start leaving numbers out around nine and ten. The clock will not measure time correctly.

What is the chance that I will have a baby with a Trisomy at my age?

This is a very simple calculator that gives you the risks at your age. As you see, the chances for a Trisomy go up substantially for each year over 35.

What tests are available to me?

First let’s discuss the difference between a test and a screen. The AFP, NT Scan, and ultrasounds are screens. This means that they give you a ratio of the possible risk that your baby may have a chromosomal anomaly. This is not a proof positive diagnosis. The CVS (Chorionic Villi Sampling) and Amnio (Amniocentesis, FISH test) are considered diagnostic tests.


The earliest non invasive test available is the nuchal translucency scan. It can only be done between 11 weeks 0 days and 13 weeks 6 days, so if you choose to have this screen done, you should ask for it very early in pregnancy in order to have it scheduled with your perinatologist. When preformed at the right time and accompanied with the blood work available it is a very accurate screen. ... ap01-3.htm

AFP (alpha-fetoprotein) screen

This screen is done between weeks 17- 20. It is also referred to as the triple screen. The triple test is measuring high and low levels of AFP and abnormal levels of hCG and estriol. The results are combined with the mother's age and ethnicity in order to assess probabilities of potential genetic disorders. The AFP is known for its HIGH false positives. ... pplus.html


Most of you will have an ultrasound at some point in your pregnancy. Baby is measured and organs are watched for development. There are many types of ultrasound. Sometimes in the office the doctor may just ‘take a quick peek’ to see the heart beating and that the baby measures correctly for dates. An ultrasound tech may do a more in depth u/s or your doctor may refer you to a perinatologist to have a level two ultrasound, which really only means they take a lot more measurements and are looking for specific signs of health in baby.

A 3D ultrasound is one that the computer takes the u/s information and generates a three dimensional image of what your baby looks like. They are usually done for the fun of seeing your baby’s face and are at this time not usually used for medical diagnosis. A 4D ultrasound is one where you get to see the computer generated image actually moving. You may receive a dvd souvenir to take home with you!


CVS (Chorionic Villi Sampling)

This test is considered diagnostic, however, can still provide false positives in a mosaic diagnosis. If a child is diagnosed with mosaic Trisomy, this means that some of the cells are effected and some are not. If the CVS is taken from the placenta, it is possible that only the placenta is effected by the Trisomy and the baby could be perfectly healthy. The risk of miscarriage is also higher with CVS than with amniocentesis. The CVS is preformed much earlier in pregnancy, between 10-12 weeks.

Amnio (Amniocentesis, FISH test)

Amnio is considered to be the most accurate test. From the time of draw to results can take about two weeks. If requested at the time of draw, an addition test called the FISH can be done. This is accelerated and considered to be preliminary only but results can be received in as little as two days. Many insurance companies will not cover the FISH test to be added. Most labs charge about $100 dollars for this test so for some families it is worth the cash out to have the results faster, and for many, since the results are not conclusive they prefer to wait the two weeks. An amnio actually looks at the chromosomes themselves. They take a large sample of chromosomes from the amniotic fluid to grow and look at many cells to see if all the cells are effected or healthy or if some of each exists. ... 20amnio%20

PostPosted: Dec 02, 2006 2:30 pm
by AmberWest
Jenny, could you please sticky this post so it will remain at the top? I feel this is something that will come up frequently and should be easily found. Thanks for all your research. :D

PostPosted: Dec 03, 2006 12:55 pm
by carla
thanks for all the info Jenny!!! :hugs:

PostPosted: Dec 03, 2006 5:24 pm
by Jenny
Actually Amber, you are Carla are the only two who can sticky it! :wink: I am not a moderator in this forum, but I do agree it would be great to sticky it and also keep it open for people to reply with their personal experiences. I think Suzanne has gathered a ton of those for us.

PostPosted: Dec 03, 2006 9:25 pm
by AmberWest
Hmmm... okay, very strange because no matter where I look in this post I'm unable to find the sticky option where it usually is. GAH!

WENDY help help help! :oops:

PostPosted: Dec 03, 2006 9:26 pm
by carla
I can't find the sticky thing either. Are you sure you can't do it Jenny?

PostPosted: Dec 03, 2006 11:49 pm
by Jenny
I think you have to edit my original post and look at the bottom and there will be an option for sticky.

PostPosted: Dec 04, 2006 10:25 am
by AmberWest
YAY! Got it, FINALLY. :oops: Once again, thanks for all the hard work Jenny. I'm sure this will help alot of women who are going through these tests etc.

PostPosted: Dec 04, 2006 7:17 pm
by carla
Way to go Amber!!! I couldn't find it for the life of me :D

PostPosted: Dec 05, 2006 8:00 am
by IslandDreamer

PostPosted: Apr 15, 2007 1:05 am
by IslandDreamer