Elaine Stillerman, LMT
During your pregnancy, your examinations will include many different types of prenatal tests to determine if there are any maternal or fetal complications. Blood is screened at the first visit to rule out conditions that could harm your baby, such as hepatitis B or syphilis. You will also be checked for anemia. Certain genetic tests can also be done with the blood sample if indicated. A test for HIV may be offered and is optional.
You will be asked to give urine samples at each check-up. The technician will look for bacteria in the urine, which could indicate the presence of a urinary tract infection (UTI). Up to 10% of pregnant women will have positive results. If an infection is present, it can be easily treated with antibiotics. The concern is to stem the spread of the infection to the kidneys where the risk is much higher for you and your baby. The presence of protein in the urine is also a risk factor. This could mean a UTI or a very dangerous condition called pre-eclampsia in later pregnancy.
Your blood pressure will be taken at each visit and you will be weighed to monitor a safe and adequate weight gain. One way to confirm the pregnancy is through the use of the Doppler sonogram to listen to the baby's heartbeat. Ultrasound uses sound waves to send back pictures from within the uterus. With ultrasound, you can actually see your baby's heart beat and movements.
The ultrasound can also be used to measure the clear space in the tissue at the back of the neck. This is known as the nuchal translucency screening test. The transducer is positioned so the nuchal fold area is visible on the monitor and the thickness is measured with calipers. This measurement can be used to assess the risk of Down syndrome (DS) and other chromosomal disorders. Babies with abnormalities tend to accumulate more fluid in the back of their neck during the first trimester, enlarging the clear space. This screening is done between 11-14 weeks before a more invasive chorionic villi sampling (CVS) or amniocentesis. The last day is can be done is 13 weeks and 6 days and is 80% effective.
A few advanced medical centers include an additional factor in the risk of DS and examine the fetal nasal bone. If the nasal bone is not formed between weeks 11-14, the fetus has an increased chance of DS. This marker, along with the mother's age, baby's age, nuchal fold measurement and blood tests can bring the accuracy of the diagnosis up to 97%.
You might hear your doctor speak of the 'triple screen'. This test is offered to all pregnant women between 15-18 weeks and is used to identify higher than average risks of certain serious birth defects such as neural tube defects (spina bifida) and DS. It is a simple test where blood is drawn and 3-4 substances are measured.
Chorionic villi sampling (CVS) is performed between 10-12 weeks after a woman's last menstruation. This test is not a routine obstetric procedure and is offered to women who demonstrate an increased risk of chromosomal or genetic birth defects. Some reasons for doing CVS are:
· Maternal age. DS occurs 1 in 1,250 to women in their 20's, 1 in 400 by age 35 and 1 in 100 at 40. Over 45, 1 in 50.
· Previous child or pregnancy with birth defect
· Family history
· Want results early in pregnancy
A small piece of chorionic villi (tissues that attach the amniotic sac to the walls of the uterus) is extracted by a needle inserted through the vagina. The risk of miscarriage is between 1 in 200 to 1 in 100.
The most common prenatal test to diagnose chromosomal and genetic defects is the amniocentesis. This is not a routine obstetric procedure either and is offered when there is an increased risk of chromosomal or genetic birth defects:
· Maternal age (generally over 35)
· Previous child with birth defect
· Suggestive screening results from other genetic tests
· Family history
This test is given between weeks 15-18. A thin, hollow needle is inserted through the abdomen into the uterus. 1-2 tablespoons of amniotic fluid is extracted. An ultrasound is used to make sure the needle doesn't puncture the fetus. There may be some cramping, spotting and possible leakage of amniotic fluid after the procedure. Patients are advised to rest for a few hours afterwards. The risk of miscarriage after the procedure is 1 in 400 to 1 in 200.
More advanced genetic testing can also be done through blood sampling. DNA tests are the newest and most sophisticated may to test for genetic disorders. DNA testing is done to:
· Test for carrier screening to identify unaffected individuals who carry one copy of a gene for a diseases that requires two copies for the disease to be expressed, such as Tay Sachs.
· Pre-implantation genetic diagnosis to test for abnormalities in the embryo that was created in vitro.
· Prenatal diagnostic testing for syndromes such as Fragile X or PKU.
· Newborn screening
In the United States, there are no regulations for evaluating the accuracy of genetic testing. Most genetic tests developed by laboratories are categorized as services the FDA does not regulate. Only a few states have established guidelines.
Every woman receives glucose screening and glucose tolerance test to check for gestational diabetes mellitus between weeks 24-28. The initial screen does not provide a diagnosis, but rather identifies who needs further testing. Women drink a sugar solution that contains 50 grams of glucose After 1 hour, a blood sample is drawn to see how efficiently her body processed the sugar. A high reading, which happens 15-23% of the time, indicates the need for the three-hour glucose tolerance test. Women drink a solution containing a known quantity of glucose. Blood is taken before the women consume the solution and drawn again every 30-60 minutes up to 3 hours.
Some doctors perform the test for toxoplasmosis as a regular part of their obstetric care, while others don't. Toxoplasmosis is a parasite ingested from soiled cat litter or unsanitary food preparation. This is a simple blood test that looks for the antibody to toxo. Serious birth defects may be likely if the fetus was infected between weeks 10-24.
All these tests can produce anxiety for some women. Waiting for tests results can be rather stressful. But knowing that you and your baby are healthy is usually worth the wait. | 
