PRENATAL SCREENING: WHO IS AT RISK? -

Fortunately, most babies are born healthy. However, as all prospective parents are "at risk," it is natural to want to clarify any unique concerns. The real questions for most couples are: do we face a higher than expected or higher than baseline risk? If so for what? Do we have options to deal with these risks? Prenatal screens are used to make this determination. Those identified as facing an increased risk are offered follow-up testing and/or genetic counseling to clarify, diagnose, or exclude the concern. Having this knowledge helps some couples plan, prepare or make management decisions for their baby.

BASELINE RISK: Of all babies born, 3-4% have some type of birth defect and 2-3% are described as mentally retarded. This is a minimum risk faced by all regardless of health, family history and exposures. No prenatal blood test, no ultrasound, no amniocentesis can diagnose or exclude all such problems but your doctor will use several screening techniques to determine if your baby faces a higher than expected risk for any particular problem and to see if you would benefit from genetic counseling and/or should be offered further testing.

**IT IS IMPORTANT TO REMEMBER SCREENS ARE NOT DIAGNOSTIC TESTS, THEY JUST ASSESS RISK. A POSITIVE SCREEN IS ONE THAT INDICATES YOU ARE IN A ìHIGHî RISK CATEGORY AND A NORMAL OR NEGATIVE SCREEN IS ONE THAT INDICATES NO HIGH RISK IS FOUND. A POSITIVE SCREEN DOES NOT DIAGNOSE A PROBLEM AND A NEGATIVE SCREEN DOES NOT RULE OUT THE PROBLEM.

WHEN A SCREEN IS ABNORMAL OR POSITIVE IT CAN RAISE ANXIETY UNTIL FURTHER DIAGNOSTIC TESTING RESOLVES THE CONCERN. IT MAY ALSO RESULT IN THE NEED TO MAKE CHOICES ABOUT ADDITIONAL TESTS, SUCH AS AMNIOCENTESIS OR OTHERS. THESE ADDITIONAL TESTS ARE DIAGNOSTIC TESTS, NOT SCREENS AND MAY BE HELPFUL FOR YOUR OWN PEACE OF MIND, FOR PREPARATION TIME AND/OR FOR PREGNANCY CARE AND MANAGEMENT DECISIONS. AT EVERY STEP, COUNSELING IS AVAILABLE TO CLARIFY RISK AND OPTIONS. (An example of a screen is a breast self exam. A positive screen is finding a lump. This can make you nervous but most likely you do not have cancer. Your may, however, need a breast exam by your doctor, or a mammogram but a biopsy would be the diagnostic test to be sure.)

EXAMPLES OF PRENATAL SCREENS:

1. Family history and ethnicity: A family history of certain birth defects, medical illnesses, genetic disorders, mental retardation or other problems may suggest an increased risk to you/your spouse/other relatives or your baby. Genetic counseling will help you determine if there is an increased risk and what tests are available to provide reassurance. In every ethnic group there are certain problems, disorders or diseases that occur more commonly. Therefore, depending on your ethnic background, you may be offered the option of additional testing. (For example, all couples should be offered carrier testing for cystic fibrosis because the frequency of carriers is high. Most couples do not know they are carriers until they have an affected child. You can get more information about this disease, the test, your options or other carrier tests that you should be offered from your doctor).
2. Parental age: Most birth defects and retardation do not increase in frequency with age, but a special type of chromosome problem does occur more frequently in the offspring of women as they get older. Down syndrome is the most common example but not the only one. If you are 35 or older at delivery, you have a positive age screen and you will be offered the option of diagnostic testing to know for sure. A different category of genetic problems (new gene mutations) occurs more often with increasing paternal age, but there is no diagnostic testing to address this category of risk.
3. Exposures: Most birth defects and retardation are not due to anything mom does or does not do, but your doctor will ask you if you have been exposed to any medication (prescription or non-prescription), chemicals: in the work place, alcohol, or other drugs, infections or illnesses or other factors that may increase the chance of problems in your baby. The chance of harm depends on the exposure, the timing, and the does and varies between people. There may be some testing that is appropriate to offer if a risk is identified.
4. SERUM SCREENS: A serum screen is a blood test offered to a pregnant women in an attempt to do three things: a) to try to identify most babies with spina bifida as this may influence where and the baby is delivered. Most babies with spina bifida (98%) are born to unsuspecting parents with no previously identified high risk factors. A serum screen can identify most babies affected with spina bifida. A positive screen means a follow-up ultrasound or amniocentesis will be offered to clarify the concern, it does not mean the baby has a problem (remember, just like a breast lump!); b) The serum screen can also provide a more precise assessment of the chance your baby has Down syndrome and some other chromosome problems. A positive screen is merely one that suggests the risk is higher than that faced by someone who is 35, and a negative screen suggests the risk is less than that faced by a 35-year-old. The older you are the greater the chance of a positive screen. The blood screen is not intended to diagnose or exclude chromosome problem. Those with positive screens are offered follow-up diagnostic testing such as amniocentesis. (If you are already identified as high risk based on age or history these screens are NOT intended for you and are usually not adequate to address the concern); c) The screen can also help identify some women who may be in need of increased surveillance in the third trimester because of fetal placental problems. A positive screen would warrant further assessment.
5. ULTRASOUND: While ultrasound can be used as a diagnostic test for some physical malformations, it is often used as a screen to determine if further testing is necessary. Sometimes subtle differences between babies, like their fluid volume, their growth and so forth are just individual variation but sometimes these differences may be due to an underlying genetic disorder and further testing will be offered to clarify. (Keep in mind that ultrasound cannot diagnose genetic or chromosome problems, nor exclude them. For example, half of babies with Down syndrome will have a normal ultrasound scan, and most babies with ultrasound findings do not have Down syndrome or other more serious underlying problems). Even when a physical defect is identified, further testing such as amniocentesis will be offered to try to determine the cause, as this may help in assessing prognosis.

WITH ADVANCES IN MEDICINE AND GENETICS WE MAY SOON HAVE BETTER SCREENING AND DIAGNOSTIC TESTING. HOWEVER, MOST SCREENS ARE DESIGNED TO BEST DETERMINE WHO WOULD BENEFIT FROM DIAGNOSTIC TESTING SO WE CAN OFFER THESE TESTS MORE INTELLIGENTLY. (MOST PARENTS WHO HAVE CHILDREN WITH PROBLEMS HAD NO OBVIOUS RISK FACTORS TO WARN THEM: SPECIFICALLY NO FAMILY HISTORY, AGE, OR EXPOSURE RISK FACTORS, SO SCREENS SUCH AS SERUM SCREENS AND ULTRASOUNDS MAY HELP ALERT SUCH UNSUSPECTING PARENTS. BEFORE BEING TESTED FOR ANY CONDITION YOU SHOULD UNDERSTAND WHAT THE DISORDER IS AND WHAT MIGHT BE INCLUDED IN THE CLINICAL SYMPTOMS, WHAT THE RELIABILITY OF THE TEST IS, WHAT OPTIONS, INCLUDING TREATMENT ARE AVAILABLE IF THE DISORDER IS FOUND??

IF YOU HAVE ANY QUESTIONS ABOUT YOUR OWN PERSONAL RISKS, THE GOALS-BENEFITS-LIMITS OF SCREENS, ASK YOUR DOCTOR OR GENETIC COUNSELOR. MANY OF THESE SCREENS ARE OPTIONAL.