This test is used to identify pregnancies that may be at higher risk for Down syndrome, spina bifida and Trisomy 18. The spine problem (spina bifida) occurs when the fetus (baby in your womb) doesn’t form a complete covering around the major parts of the nervous system (brain and spinal cord). It may lead to various physical problems ranging from needing braces to walk, to severe handicaps including not being able to walk, as well as mental problems and even death.
Down syndrome means the baby has an extra chromosome 21. Down syndrome causes mental retardation, heart abnormalities and other birth defects.Trisomy 18 is due to an extra 18 chromosome and causes mental retardation and other abnormalities more severe than Down syndrome.
The decision to have the test done is left up to you. In this country, the overall chance of having a child born with the spine defect is about 1 to 2 out of every 1000 babies born. However, if you, or the baby’s father, or any relatives have had a child with spina bifida, the chance goes up. Even though there is an increased risk of having a spine defect because of a family history, most of the children with spine defects are born to couples without anyone in the family having had it. If you have ever had a child with anencephaly (where the brain and scalp do not develop normally), this is considered a type of spinal defect and should be reported to your doctor. The chances of having a child with Down Syndrome and Trisomy 18 are about 1 in 800 for all women, but chances are higher for women who are over 35 years of age. In general, as you get older, your chances of having a child with a chromosome problem increases.
If you begin your care before you reach 14 weeks of pregnancy, you will be offered other tests that are explained in the instruction sheet B1 1st Trimester Screening.
The test is most accurate between 16 and 18 weeks of pregnancy. This allows us to give you counseling about the choices open to you if a problem is found.
An abnormal screen does not necessarily mean that the fetus has a problem, but it means your risk is higher. An abnormal risk may mean there is incorrect dating of your pregnancy or you may be carrying more then one fetus. Your doctor may suggest a more detailed ultrasound test to look at the fetus or more testing may be offered to make sure the fetus doesn’t have Down syndrome, spina bifida or other chromosome problems. After you have read this material, you should discuss any questions with your doctor or medical staff.
Your doctor will explain the possible meanings of the abnormal test and order some further tests, which may include ultrasonography and/or an amniocentesis, to help discover the cause of the abnormal test. The decision of having these other tests done will be left up to you. If you decide to have further testing done, your doctor may do the testing or send you to a specialist.