Pregnancy A to Z - Genetics

Each of us is made up of genes from our parents, and our parents are made up of genes from their parents, and so on. Genes are kind of like the blueprints for what we will look like and how healthy we will be. You'll be glad to know that most parents don't have a very high risk of passing on a "problem" gene. If you're over 35, or if your family has a history of some kind of hereditary problem, your provider will probably schedule genetic counseling and some type of genetic screening so that you can be aware of any potential problems.

The most common genetic test is an amniocentesis, also called an "amnio". Your provider uses a needle to withdraw some of your amniotic fluid, which is the liquid that surrounds your baby. Most women comment that the test sounds worse than it really is. The cells in this fluid contain all of the information your provider needs to check for possible problems like Down Syndrome or spina bifida.

Another genetic test is called CVS, chorionic villus sampling. This test can be done earlier in your pregnancy, and like amniocentesis, looks for genetic problems.

Every cell in your body contains DNA, which is a blueprint or "genetic code" that tells your cells what to do and how to grow. Each cell in your body contains the entire code. It's hard to imagine, but in each and every cell there are 5 - 6 million different genes. This is a huge amount of information that is condensed into more easily managed units called chromosomes. Each of us has 46 chromosomes that pass the genetic code from cell to cell as our bodies grow.

Just as chromosomes pass genetic material when your body makes new cells, they also pass the genetic code from you to your child. When you ovulate each month, your egg has 23 of the chromosomes needed to make a person. When you become pregnant, the other 23 chromosomes come from the father's sperm. With a total of 46 chromosomes, your baby now has the information he needs to grow.

This information, or genetic code, will decide things like how tall, what color of hair, and what color of eyes your baby will have. Whether your baby is a boy or a girl is also decided by the genetic code that came from you and your baby's father. Unfortunately, some conditions or diseases can also be passed on through your genes.

Genetic screening may give you some important information about the health of your baby. People who carry traits, or genes, for genetic disorders don’t usually show symptoms. If both parents are carriers for the same genetic trait, there is a chance that their baby could have the genetic disease. A special blood test may be able to tell you if you carry a trait. If you are concerned, feel free to ask your provider for more information about genetic carrier screening.

Amniocentesis can be done most safely after the 15th week of your pregnancy. This test makes sure your baby isn’t affected by Down syndrome, spina bifida or has other genetic problems. The procedure involves taking a sample of the amniotic fluid that surrounds your baby. This fluid contains cells that can be tested for information about how your baby is developing. A needle is passed through the mother's skin and abdominal wall, into the uterus, and then through the fetal membranes into the amniotic fluid. Because your provider will use an ultrasound to guide him, it is very unlikely that the needle will stick your baby. If you're having fetal chromosome testing done, the test results can take 1-3 weeks to get back. Amniocentesis has a miscarriage rate of less than one in two hundred. An "amnio" is typically not very painful and most women comment that it's much less painful then they expected.

A test called chorionic villus sampling, or CVS can be done when you are 9 to 12 weeks along in your pregnancy. The benefit of CVS is that it is the earliest test for genetic problems. Your provider will take a tiny tissue sample of the placenta from inside your uterus to detect Down syndrome, sickle cell anemia, cystic fibrosis, and others. You will generally have the test results within ten to twelve days after the test. The risk of losing your baby as a result of CVS is approximately 1%.