1st Trimester Tests and Procedures
1st Trimester Tests and Procedures
For special genetic or medical reasons, you may need other lab tests, like blood or urine tests, cultures for infections, or ultrasound exams in the first trimester. Your doctor will discuss them with you during your visits.
The most common tests recommended in the first trimester include:
Nuchal translucency screening (NTS)
This new type of screening can be done between 11 and 14 weeks of pregnancy. It uses an ultrasound and blood test to calculate the risk of some birth defects. Doctors use the ultrasound exam to check the thickness of the back of the fetus’ neck. They also test your blood for levels of a protein called pregnancy-associated plasma protein and a hormone called human chorionic gonadotropin (hCG). Doctors use this information to tell if the fetus has a normal or greater than normal chance of having some birth defects.
In an important recent study, NTS found 87% of cases of Down syndrome when preformed at 11 weeks of pregnancy. When NTS was followed by another blood test in the second trimester ( the maternal serum screening test), 95% of fetuses with Down syndrome were able to be identified.
Like all screening tests, the results can be misleading and return “false positives”. In 5% of women who have NTS, results show that their babies have a high risk of having a birth defect when they are actually healthy. This is called a false positive. To find out for sure if the fetus has a birth defect, NTS should be followed by a diagnostic test like chorionic villus sampling (CVS) or amniocentesis.
NTS is not in widespread use. If you are interested in NTS, talk to your doctor. If she is unable to do the test, she can refer you to someone who can. You should also call your insurance company to find out if they cover the cost of this procedure. NTS allows women to find out early if there are potential health problems with the fetus. This may help them decide whether to have follow-up tests.
Chorionic villus sampling (CVS)
CVS is performed between 10 and 12 weeks of pregnancy. In CVS, the doctor inserts a needle through the abdomen or a catheter through the cervix to reach the placenta. The doctor then takes a sample of cells from the placenta. Experts use this sample to look for problems with the baby’s chromosomes. This test cannot find out whether your baby has open neural tube defects. CVS is not without risk - about 1 in 200 women have a miscarriage as a result of this test.
