Our dream as expecting parents is to have a happy, healthy child.  Fortunately, about 97% of the time, our babies are born perfectly healthy. However, sometimes during the course of pregnancy, a routine screening or genetic counseling session may raise concerns about the health of our baby.  Our doctor may then suggest to us the option of additional diagnostic testing .  It is important to have as much information about screening tests and diagnostic tests in order to make the best decision for your situation.

Screening tests for birth defects:

AFP (also called alpha feto protein):

The AFP screening test (alpha feto protein) is a common blood test that is routinely offered to all mothers in many practices. This  screening test is usually performed at about 15-20 weeks of pregnancy.  AFP is a substance that is produced by the fetal liver. It crosses the placenta into the mother's bloodstream and can be measured by a talking a blood sample from the mother. By analyzing the level of AFP in the blood sample, a doctor can inform the expecting parents whether their child may be at a higher risk for neural tube defects (which would elevate the level of AFP), anencephaly (absence of a brain) or down syndrome (which causes a lower than normal level result).  

Many doctors offices are now using what is called an AFP profile (also known as the "pyramid" or "triple marker" test.)  This screening test uses the level of 3 substances found in the maternal bloodstream: AFP, human chorionic gonadotropin and unconjugated estriol. This test is correlated with age of the mother and length of gestation to generate an approximate risk of your child having down syndrome. This test has a slightly higher reliability than the AFP test alone for detecting down syndrome.  A measure of the AFP alone is used to detect open neural tube defects.  This screening test is usually performed between the 15th and 18th week of pregnancy (with 16 weeks being the average).

It is important to remember 3 things about either AFP test:

1) It is optional.  You do not have to have this test performed unless you choose.

2) It is only a screening, and not a diagnostic test.  This means that it can identify some women who are at higher risk of carrying a child with a neural tube defect or down syndrome, but not all women.  It identifies approximately 90% of open neural tube defects and about 60% of down syndrome cases. It is not a guarantee that no birth defects are present.  However, it should be considered somewhat reassuring.  Remember, 97% of babies are born healthy.

3) An abnormal test result does not necessarily mean your child has a birth defect, just as a normal result does not guarantee a healthy child. The test has about a 5% rate of "false positive results".  This means that the screening may indicate that your child is at high risk for a birth defect when in fact your child is perfectly healthy.  High levels of AFP are also found in some cases of threatened miscarriage and in mothers who are carrying twins. Unfortunately, it also has "false negative results", where a child who does have a neural tube defect or down syndrome is not identified by the test results.

Ultrasounds (Sonograms):

Ultrasounds are a type of diagnostic tool that uses high-frequency sound waves to create pictures, known as sonograms, on a computer screen or TV. monitor. In the most common type of ultrasound, the examiner places a small amount of warm gel on your stomach in order to move a small hand held transducer back and forth in order to send out sound waves that bounce off the fetus and create an image of your baby in motion on the screen.  A transvaginal ultrasound is also used in early pregnancy where the transducer is inserted into the woman's vagina in order to provide a picture of the embryo and to provide important information about very early development.  It may be vaguely uncomfortable but not painful. Many women do not find it uncomfortable at all, or are at least too distracted by seeing a first glimpse of their baby to notice.

Ultrasounds are used for various reasons depending on the stage of pregnancy.  In early pregnancy, it is used to determine the viability and location of the fetus and placenta, and to rule out other conditions such as an ectopic pregnancy (where the fetus attaches outside the uterus.) It can also be used to screen for various birth defects, determine the size of the fetus, to determine if their are multiple fetuses, and to provide or confirm the due date.  Later in pregnancy an ultrasound is commonly performed (about 20 weeks gestation is average) in order to detect  certain structural abnormalities, to make sure the fetus is measuring on schedule with the estimated due date, the sex of the fetus, etc.

A level 11 ultrasound is similar to a general ultrasound described above.  The main difference is that it is performed with much more advanced equipments so that the fetus can be seen in more detail. A level 11 ultrasound is usually the next step for women who have received an abnormal result on the AFP test.  It is also indicated for women who have a questionable general sonogram finding, have a history of birth defects or miscarriage, or if a genetic consultation warrants further investigation. The level 11 ultrasound is able to screen for birth defects with more accuracy than a general ultrasound, and the examiner is usually a fetal-maternal specialist or peritologist who specializes in high risk pregnancies.  The level 11 ultrasound last about 20-30 minutes.  The procedure involves examining the fetus in detail, with special attention being given to the area of concern.  A level 11 ultrasound can usually help to alleviate the concerns the woman or doctor may have, but occasionally some findings are discovered that may prompt the doctor to suggest more invasive diagnostic testing such as amniocentesis or chorionic villus sampling.  Both of these procedures are optional and carry a small risk of miscarriage, so a consultation with a genetic counselor in order to discuss the situation is required before either test can be performed.

Ultrasound has long been considered a safe procedure, and no harmful effects have ever been reported.  There is no data on long term effects of the use of ultrasounds, so it is always wise to avoid unnecessary ultrasounds to be conservative. Do not hesitate to ask your doctor for his reason for scheduling an ultrasound if you are unsure, and ask any questions you may have about the results.

When additional tests are recommended:

Your age is one factor in deciding if additional tests should be performed.  Birth defects, specifically down syndrome, increase with the age of the mother.  Studies have found that the age of the father can also play a role, although to a much smaller extent. A mother who has a baby at age 40 has  much higher chance of having a child with down syndrome than a mother at age 20.  For this reason, women age 35 and over are generally offered a diagnostic test called an amniocentesis.

 Amniocentesis and chorionic villus sampling are more invasive tests that are usually reserved for when there is an indication that something may be wrong and more testing is needed. These tests help to diagnose various problems or complications such as birth defects.

Amniocentesis:

What is amniocentesis? Amniocentesis is a diagnostic procedure that is performed in order to detect certain birth defects.  It is most commonly used between the 13th to 16th week of pregnancy in order to detect the presence of down syndrome in women who are known to be at higher risk.  These women include those who are over the age of 35, those who have family histories of down syndrome, and those whose screening test (AFP or ultrasound) indicate higher risk. Amniocentesis can also test many chromosome abnormalities, neural tube defects and other diseases such as Tay-Sachs and sickle cell anemia. An amniocentesis can also be used in later pregnancy to assess the maturity of the fetus.

How is the procedure performed? The doctor performing the procedure will first use an ultrasound in order to determine the exact location of the fetus.  Once the position of the fetus and placenta are identified, a long needle is inserted through the uterus and amniotic membrane that surrounds the fetus.  A small sample of amniotic fluid is taken out through the needle for lab analysis.  The use of ultrasound during the procedure ensures that the needle is inserted away from the fetus and placenta.  For this reason, fetal injury is very rare.

How long does the procedure last? The entire procedure only takes about 10-20 minutes on average.  Most of this time is spent identifying the fetal position on ultrasound.  The time it takes to insert the needle and extract the fluid is only a minute or two.

Are there circumstances when the amniocentesis can't be performed? Yes.  On rare occasions, the fetus may not be in a position where it is considered safe to insert the needle to obtain the sample of amniotic fluid.  Also, about 105 of the time, the needle is inserted but the amniotic fluid is unable to be drawn.  In this situation, the doctor will either try to insert the needle one more time or he will suggest that you return again for another attempt later in the week.  The doctor will never try more than twice on any one occasion because of the increase risk of miscarriage.

How does having an amniocentesis determine whether my baby has a birth defect? The amniotic fluid that is taken during the procedure contains fetal cells.  These cells are taken to a lab and cultured in order to determine if any abnormalities are present. 

How long does it take to get the results? In most cases, you will have the laboratory results back within 10-14 days.  It takes about 10 days to culture the cells in the lab in order to make the diagnosis, therefore it is best to wait the full 10 days before calling your doctor to find out if the results are back.

Are there any complications/risks of an amniocentesis?   Yes, having an amniocentesis performed does involve some risks.  Risks include infection, trauma or injury to the fetus (very rare with the use of ultrasound), rupture of amniotic membrane and miscarriage.

Complications/side effects may include:

1) fever over 100 degrees (which may indicate an infection)

2) gushing or steady leaking of amniotic fluid (which may indicate rupture of the membrane).  This may also be caused by the temporary leaking of excess amniotic fluid that was released when the needle was inserted. This side effect is more common and occurs in about 1% of women who have an amniocentesis.

3)sever or continuous cramping (more than 2 days), or cramping that gets progressively worse.

Any of these complications warrant an immediate call to your doctor for further advice.

Miscarriage as a result of having an amniocentesis is reported to occur in no more than .5% of cases ( which is about 1 in every 200 women).  It is considered a relatively safe procedure for those who are at higher risk of having a baby with a birth defect.

It is not recommended for women at low-risk of having a child with a birth defect because of the risk of miscarriage.

What women are candidates for an amniocentesis?

1) Women age 35 and older. Certain birth defects, such as down syndrome and other chromosomal abnormalities are known to increase with age.

2) Those who have an abnormal AFP result and whose level 11 ultrasounds warrant further diagnosis.

3) Women who have a history of miscarriage or family members with birth defects. 

4) Women who are known to be at higher risk of having a child with a birth defect based on the information obtained from a session with a genetic counselor.

Remember:  Amniocentesis is an optional procedure.  It can be recommended or suggested but is never required.  This is a personal choice that you and your loved ones must decide on your own.

Chorionic Villus Sampling:

Chorionic Villus Sampling is a diagnostic pre-natal test that is performed during the first trimester, usually between the 8th and 12th week of pregnancy.  The test is used to test for genetic abnormalities (birth defects) by removing a small amount of fetal tissue from the placenta.

How is it performed? An instrument is placed through the abdomen or cervix.

How does having CVS performed determine whether or not my baby has a birth defect? The samples of placental tissue is sent to a lab and cultured to assess whether the fetus has any birth defects.

Are there any risks of having Chorionic Villus Sampling performed? Yes.  The risk of miscarriage is between 1 and 2 percent. 

How long do I have to wait for the results? The complete results are available in about 1-2 weeks, although preliminary results are available in about 2 days for the detection of down syndrome.

What are the advantages and disadvantages between an amniocentesis and CVS? The advantage of CVS is that the test can be performed much earlier in pregnancy, and the preliminary results for down syndrome can be known in only a few days.  This can be an advantage, especially for women who would consider terminating the pregnancy as an option.  Disadvantages include a slightly higher rate of miscarriage following the CVS procedure than an amniocentesis, and the lesser reliability of the CVS procedure in detecting some birth defects as compared to an amniocentesis.

Pre-natal Tests:  Are they an option for you?

Pre-natal testing is optional.  It is a personal decision to be made by the parents. While some types of pre-natal testing are harmless, (the AFP blood test and sonograms are considered to be safe), others carry a risk of miscarriage.  Amniocentesis carries about a 1/2 percent risk, while chorionic villus sampling carries about a 2% risk.  For these types of invasive pre-natal tests, it is important to consider the pros and cons before making a decision. In order to decide if pre-natal testing is the right choice for your family, you may want to consider asking yourself the following questions:

1) How much information do I need to have about the health of my baby? Am I willing to risk having a miscarriage (however slight the chance) in order to gain this information? In this case it is sometimes helpful to look at the statistics and weigh the odds. If your risk of having a miscarriage is less than the risk of having a child with a birth defect, many parents consider the option.  If the risk of having a miscarriage is less than the risk of having a child with a birth defect, many doctors will not suggest having the procedure performed. No matter what the statistics say, the choice is always up to you.

2) How would I use this information once obtained? (for example, I would gather support groups before delivery, become more knowledgeable about my child's specific condition, make sure the choice of birthing hospital had adequate facilities to care for my baby, decide to terminate the pregnancy, consider adoption as an option, etc.)

In other words:  How will this knowledge effect you and your pregnancy?

3) How comfortable would I be with knowing/not knowing the results of the tests? Some women and their partners experience intense anxiety and fear in response to not knowing whether or not their baby is healthy.  These women cannot imagine surviving the rest of their pregnancy without this information. Other women and their partners are able to continue the pregnancy without this information and  prefer uncertainty to the worry that would accompany finding out that something were wrong with their baby.

3 Groups of People:

1) Those who want to know because they would want the option of terminating the pregnancy if a birth defect were found.  They would want to research the condition and consult with others in order to make an informed decision.

2) Those who want to know because the uncertainty, anxiety and fear of the unknown has become overwhelming. They would want to continue the pregnancy and would need time to educate themselves on the condition and secure the proper resources for their child before birth.

3) Those who do not want to know because the knowledge, if something were wrong, would cause undue stress.  These people would prefer to deal with whatever happens at the time of delivery and not before.  This group of people would not consider terminating the pregnancy an option for any reason.

These 3 groups may overlap to a great extent.  Many people do not know what they would do until faced with the reality of a situation.

Ask yourself what the risks are of carrying a child with a birth defect, and then what you may do with that information.  Most doctors only recommend invasive pre-natal testing (such as an amniocentesis or chorionic villus sampling) if the risks of a birth defect outweigh the risks of the procedure itself.

Final thought:  Call your doctor, have a second opinion level II sonogram, or talk to your genetic counselor.  An informed decision is the best decision.