First Trimester Prenatal Screening Tests
Standard Tests For Pregnant Women
Once a woman discovers she's pregnant, her doctor will run some routine screening tests to ensure everything is fine with both Mother and Baby, and to rule out any possible problems that could occur at the outset of the pregnancy. First trimester screening is a combination of maternal blood testing and fetal ultrasound. These tests may be used alone, or the doctor may wish to include other tests with them.
Fetal Ultrasound-Testing For NT
The fetal ultrasound test is for nuchal translucency (NT). The ultrasound scan is used to examine the back of the baby's neck for thickening or increased fluid, which indicates risk for Down syndrome (DS) and some other chromosomal abnormalities as well as major congenital heart problems. The NT scan measures the clear space in the tissue at the back of the baby's neck. If there is an accumulation of fluid, it is an indication that there are possible abnormalities. Babies with abnormalities tend to accumulate more fluid at the back of their necks during the first 12 weeks of gestation. The test must be done before the end of the first trimester, the latest date being 13 weeks and six days.
Ultrasound scans are also used to determine the dates of the pregnancy and to check for a multiple birth. The placenta is viewed to see its placement and ultrasound is used to rule out an ectopic pregnancy. The pelvic structure is checked and the uterus visually examined to ensure everything is going well.
Blood Tests Reveal Chromosome Abnormalities
The Mother undergoes two blood tests to measure two substances found in the blood of all pregnant women. The first test is a pregnancy-associated plasma protein screening (PAPP-A). The placenta produces this protein early in the pregnancy. If the levels of this protein are abnormal, the indication is increased risk for chromosome abnormality. The second blood test is for the human chorionic gonadotropin (hCG) hormone, also produced by the placenta in early pregnancy. Again, abnormal levels of this hormone may indicate an increased risk for chromosome abnormality.
Chromosome abnormality may manifest ultimately in miscarriage, or in birth defects such as Down syndrome, trisomy 18 or trisomy 13. The chromosomal issues have the potential of shortening the lifespan of the baby and definitely affect mental and physical capabilities as the baby grows.
If the first trimester screening tests offer abnormal results, genetic counseling is usually recommended. Additional testing that would include an amniocentesis, chorionic villus sampling, and more ultrasounds are needed to make a diagnosis.