Amniocentesis
Amniocentesis is a test that involves taking a small amount of amniotic fluid from the uterus or womb. This fluid contains some of the baby’s skin cells that have washed off and are floating in the fluid. The laboratory can look at these skin cells under a microscope and learn more about the health of the baby. These cells can be examined to detect chromosomal abnormalities or can be tested for certain genetic conditions through DNA testing. The risk for a baby to have a chromosome disorder increases with the woman’s age.
| Mother's Age at Delivery | Risk for Down Syndrome |
|---|
| 20 | 1/1923 |
| 30 | 1/885 |
| 31 | 1/826 |
| 32 | 1/725 |
| 33 | 1/592 |
| 34 | 1/465 |
| 35 | 1/365 |
| 36 | 1/287 |
| 37 | 1/225 |
| 38 | 1/177 |
| 39 | 1/139 |
| 40 | 1/109 |
| 41 | >1/85 |
| 42 | 1/67 |
| 43 | 1/53 |
| 44 | 1/41 |
| 45 | 1/32 |
Chorionic Villus Sampling or CVS (placental biopsy)
CVS is a test done by putting a small tube or catheter through the vagina and into the uterus to remove some cells from the placenta. It can also be done by putting a needle through the mother’s abdomen into her uterus and then into the placenta. The doctor decides the method and depends on factors such as the location of the placenta. The placenta has the same genetic makeup as the fetus, so testing these cells is a way to indirectly look at the baby’s cells. This test is done between 9 and 12 weeks of pregnancy.
Maternal Serum Screening (triple or quad screen, AFP plus, multiple marker screen)
The maternal serum screen is a prenatal screening test using the blood from the mother to identify women that may be at an increased risk of carrying a baby with specific birth defects, such as spina bifida, anencephaly, Down syndrome, and Trisomy 18. This test is usually done on the mother’s blood between the 15 to 20 weeks of the pregnancy and is recommended for all pregnant women.
Specific proteins or hormones (Alpha-fetoprotein, human chorionic gonadotropin (hCG), unconjugated estriol, and inhibin) are made by the baby or the placenta and are found in the mother’s blood. The levels of these proteins are linked with certain birth defects, such as spina bifida and Down syndrome. The blood test is a screening test, meaning it cannot identify a birth defect in the baby, it only indicates that the risk is higher and further testing is needed. A range of factors can influence the result of the blood test, such as the gestational age of the pregnancy or the presence of twins. It is recommended that women have an ultrasound to confirm the pregnancy dating. If the blood test is abnormal, further testing may be offered, such as amniocentesis or another sonogram.
Some facilities are performing maternal serum screening tests in the first trimester. This screening test looks at different hormones/proteins and is usually combined with ultrasound findings. Still, others use a combination of first and second-trimester screening. This combined testing is often called integrated screening.
Ultrasound or Sonogram
Ultrasound (also called a sonogram) is an imaging test used to look at the fetus. It can detect some major physical birth defects during the pregnancy, depending on the gestational age. The test uses sound waves and poses no risk to the baby. Ultrasound can verify how far along a woman is in her pregnancy. It also looks at fetal growth and can detect certain problems in the baby or pregnancy. It can be done at any time in the pregnancy, but it is usually done around 18 to 20 weeks to look for major physical birth defects.
Nuchal Translucency Screening
A nuchal translucency measurement is a procedure performed in the first trimester with ultrasound. The nuchal translucency is a fluid-filled space at the back of the baby’s neck. A large increase in nuchal translucency can be linked with an increased risk of a baby having certain problems like Down syndrome.
Percutaneous Umbilical Blood Sampling (PUBS, Cordocentesis, Fetal Blood Sampling)
PUBS is a procedure where a needle is inserted through the mother’s abdomen into the uterus and amniotic sac and then into the baby’s umbilical cord. A sample of the baby’s blood is removed from the umbilical cord and sent to a specialized laboratory for analysis. The procedure is usually done when a woman is at least 20 weeks pregnant and is usually reserved for special circumstances.