What can the quadruple screen test tell me?
The quadruple screen can tell you if your baby is at an increased risk of having certain birth defects and genetic abnormalities. If you choose to have this test, it's important to understand that a "positive" or abnormal result doesn't necessarily mean that your baby has a problem. In fact, only about one or two percent of women with abnormal results have babies with birth defects. In general, an abnormal result means only that you may need further testing, such as ultrasound or amniocentesis, to know for sure.
On the other hand, a negative or normal result is not a guarantee that your baby is healthy — but it does mean that your baby's chances of having certain birth defects are much lower. And that's why a lot of women decide to take it. Current research indicates that this test will detect 75 to 85 percent of neural tube defects (defects in the spine or head) and 60 percent of Down syndrome in babies of women younger than 35, and 75 percent of neural tube defects and Down syndrome in babies of women 35 and older.
A high AFP can mean several things. Your baby produces AFP throughout your pregnancy, and a certain amount of it should cross the placenta into your bloodstream at each stage. If there's more than expected, it often means that you're carrying more than one baby or that your baby is older than we thought. But in some cases, it's a sign of an abnormal opening in the baby's spine (spina bifida), head, or abdominal wall that's allowing more AFP to leak out. In rare cases, it can also signify a problem with the baby's kidneys. And in some cases, it doesn't mean any of those things.
A low AFP, low estriol, and high hCG are associated with a higher risk for Down syndrome (trisomy 21). Low levels of all three mean your baby has an increased risk for trisomy 18, a more severe and less common chromosomal anomaly.
If you have a high AFP, a level II ultrasound will confirm your baby's age and show whether you're carrying twins, and will allow your doctor to check your baby's spine and other parts for defects. If your baby is found to have spina bifida and you decide to continue the pregnancy, we will be able to monitor your baby's condition during your pregnancy and prepare to do surgery once your baby's born.
If you have a low AFP, the ultrasound can allow your doctor to check for several so-called "soft markers" that may suggest Down syndrome and other chromosomal disorders. These soft markers include cysts in a particular area of the brain (choroid plexus cysts), extra calcium in certain muscles of the heart (hyperechogenic intracardiac foci), a kidney problem (mild pyelectasis), a thickened nuchal fold (also called the nuchal translucency, a clear area between the back of the baby's neck and the overlying skin), an abnormally short thigh bone, and a bright-appearing (hyperechogenic) bowel.
When two or more of these markers are found, the chance that your baby has a chromosomal abnormality may be significantly higher, depending on your age and how far along you are. Also, a baby with a major structural abnormality, such as a defect in the heart or abdominal wall, has a greater chance of having a chromosomal defect.
If everything looks normal on the ultrasound, it's not a guarantee that everything is okay, but it does mean that your baby has a lower risk of chromosomal defects than average for a woman your age. You may decide that this small risk is acceptable or you may decide that you'd also like to have amniocentesis to know for sure.
If the ultrasound suggests your baby may have a chromosomal problem, your practitioner will probable offer amniocentesis to determine for sure what's going on. And if the ultrasound detects certain structural defects, you may want amniocentesis to find out whether your baby has a chromosomal problem as well, which is often the case. Amniocentesis can diagnose 99 percent of chromosomal abnormalities, but it does carry a slight risk of miscarriage (one in 200 on average). This test is usually done between 15 and 20 weeks so that the parents will have the option of terminating the pregnancy before 24 weeks if they choose to. You will probably have to wait ten to 14 days to get the results.
Still, if you're uncomfortable with this risk, you may choose to have the multiple marker with a detailed ultrasound instead. If the results of these are both normal, you may not want to go through with the amnio because the small chance that the baby will have a defect may now be less than the chance that an amnio would cause a miscarriage, just as it would be if you were younger than 35.
If you know that you would never terminate a pregnancy for any reason, you would want to think very hard about doing amniocentesis. How would you feel if you had a miscarriage from the test, keeping in mind that the baby is likely to be normal in spite of the test results. On the other hand, knowing in advance that your baby may have special needs allows you to prepare for the challenges you'll face. Knowing what's going on with your baby will allow your medical team to monitor your pregnancy as needed and to bring a neonatologist or pediatric surgeon on board to prepare to help your baby after birth.
Cons: A false positive result can worry you needlessly (this is the most common complaint about the test) and may lead you decide to undergo amniocentesis for no reason. A false negative result could make you decide to avoid further tests that would have revealed a birth defect.
Before making a decision, you'll want to discuss all of these issues with your partner, your doctor, and possibly a genetic counselor.