The first ultrasound can verify that your budding baby is alive and well, give you his or her estimated gestational age and identify multiples. From the resulting images, your doctor takes nasal bone measurements and looks for nuchal translucency (fluid behind the neck) as an early sign of Down syndrome. The ultrasound image appears as a result of measured sound waves; there is no risk involved.
Blood tests (for the PAPPA protein and hCG hormone) may be conducted at the same time as the ultrasound. At this point, the blood is tested for Down syndrome (with 91 percent sensitivity and a 5 percent false positive rate) and trisomy 13 & 18—chromosome anomalies that are associated with severe mental retardation and early infant death (with 95-98 percent sensitivity and 5 percent false detection). If the results are borderline, another screening in the second trimester may be desired.
Most women will have a second trimester ultrasound between 18-20 weeks gestation, when the baby actually starts to look like a baby! Organs and skeletal structure are visible, and the gender is often distinguishable at this time. Besides checking the baby’s position, the doctor will look for risk of congenital anomalies, such as heart defects or a cleft lip, and markers for chromosome anomalies.
A blood test for AFP (alpha-fetoprotein) level may be administered. AFP looks for neural tube defects (spina bifida and a brain disorder called anencephaly). An elevated AFP can also be associated with an under-performing placenta which can cause stunted growth. If blood tests were not conducted in the first trimester, or if you choose an integrated first-and-second trimester screening, a blood test called a Quad Screen (for AFP, hCG , estriol, and inhibin A) is recommended. This test is less accurate than the first trimester screening with only 75 percent sensitivity in detecting Down syndrome.
Amniocentesis and CVS are diagnostic tests that are sometimes recommended for older moms or, more often, following abnormal screenings during the standard blood tests. Amniocentesis is an invasive test wherein a needle penetrates the uterus to extract amniotic fluid in order to test the growth of fetal cells. It is performed between 15 and 20 weeks gestation. It identifies chromosome anomalies with 99.9 percent accuracy, but it carries the risk of membrane rupture, infection and injury to the fetus. The risk of miscarriage is 1/300 to 1/400.
CVS (Chorionic Villius Sampling) is also invasive.
It presents a higher risk of miscarriage—about 1/100 to 1/200—but can be performed earlier, between 11 and 13 gestational weeks. This test studies chromosomes taken from the placenta; it is typically just as accurate as amniocentesis, but in 1/100 cases, an amniocentesis will also be required for better accuracy.
Knowing about your baby’s health ahead of time can put your mind at ease; being aware of a disability or condition can help you to prepare psychologically, line up medical care and avoid a shock in the delivery room. Dr. Atlas advises, “Even though nothing can be done [pre-birth] for the majority of problems, it gives the parents time to understand the problems and get prepared for what lies ahead.”