A Guide To Second Trimester Tests

If this is your first pregnancy, you may find the array of tests available a daunting prospect. It's difficult to judge which tests are indicated and which tests it might be better to do without. If you're in your second trimester, read on to get a general overview of the available tests so you can make an informed choice.

Second Trimester

*Amniocentesis-Amniocentesis is a diagnostic test that may be recommended by your health care provider if you have received an abnormal result on a first trimester screen or triple screen test. This test can identify certain inherited or genetic disorders as well as establish paternity. The test is invasive and involves the insertion of a needle into the sac of amniotic fluid so that a sample of this fetal cell-containing fluid may be removed and analyzed. Results are obtained within a two week span.

The test is most often performed between weeks 14 and 20 of the pregnancy, though some facilities may perform amniocentesis as early as 11 weeks. Sometimes amniocentesis is performed in the third trimester to evaluate the baby's lung maturity, to assess the mother for uterine infections, and in the case of a baby with RH disease, to assess the baby's anemia. The risk of miscarriage is between 1 in 400 and 1 in 200.

Invasive Test

*Cordocentesis: Percutaneous Umbilical Blood Sampling (PUBS)-Cordocentesis, also known as Percutaneous Umbilical Cord Blood Sampling (PUBS), can be used to diagnose fetal abnormalities from fetal blood. The test is performed much like amniocentesis and is invasive, but instead of amniotic fluid, a sample of the baby's blood is withdrawn and analyzed through the umbilical cord. Results are available within 72 hours.

This test is performed after week 17 of the pregnancy. The test is an alternative to amniocentesis and chorionic villus sampling (CVS) where these cannot be performed. The rate of miscarriage for this test is 1 or 2 out of every 100 procedures.

Noninvasive Test

*Maternal Serum Alpha-Fetoprotein Screening (MSAFP) or Alpha-Fetoprotein Test (AFP)-This screening test doesn't diagnose but can help identify when further testing is indicated. MSAFP is a maternal blood test which is considered noninvasive. The test is performed during weeks 14 and 22 of the pregnancy, but the optimum time to have the test is between weeks 16 and 18 for the most accurate results. All women should be offered this screening test. The test can predict the possibility of various abnormalities which require further testing to confirm or disprove. An abnormal result does not indicate that anything is wrong with your baby. Only further testing can diagnose abnormalities of the fetus.

*Quad Screen- The quad screen test is another maternal blood test that screens for four substances: AFP, hCG, Estriol, and Inhibin-A. The test is performed between weeks 16 and 18 of the pregnancy. The test screens for potential genetic abnormalities, is noninvasive, and recommended for all expectant mothers.

*Triple Screen test: Multiple Marker Screen- Also called Triple Test, Multiple Marker Screening and AFP Plus-This noninvasive maternal blood screening test looks for three substances: AFP, hCG, and Estriol and is performed between weeks 15 and 20 of the pregnancy. The most accurate results are obtained between weeks 16 and 18. The only difference between this test and the quad test is that only three out of four substances are sought. All women can and should be offered this test.


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