First trimester screening is a prenatal test that helps predict how likely it is that your baby could have a chromosomal abnormality such as Trisomy 21 (Down syndrome), Trisomy 13 or Trisomy 18. It is recommended that all pregnant patients be offered prenatal screening for chromosomal abnormalities, but it is not required that a patient have screening, and many patients opt not to have any such screening. The reason that all patients are offered screening is that most newborns with the above chromosomal abnormalities are born to women who have no obvious risk factors for those chromosomal abnormalities. The screening tests can give a more accurate prediction of the likelihood of a chromosomal abnormality and, if there is a higher than expected risk, additional, definitive testing can be offered by techniques such as chorionic villous sampling or amniocentesis.
First trimester screening includes first doing an ultrasound measurement of the baby; there is a “clear” are beneath the skin on the back of the baby’s neck (the “nuchal translucency”), that tends to be wider when a baby has Down syndrome. Maternal blood is then drawn by a "finger stick" (like checking a blood sugar level). The maternal blood is evaluated for levels of pregnancy proteins and hormones which tend to be either higher or lower when a baby has a chromosomal abnormality. The ultrasound and blood measurements are then combined to give an estimate of risk.
To avoid inaccurate ultrasound measurements, rigorous training is required before an ultrasound unit is certified to do the nuchal translucency measurement. Currently, Rocky Mountain Perinatal Associates is the only ultrasound unit in Missoula that is certified in performing this test. The test is performed between 11 and 14 weeks gestation. The results usually require 2 to 4 days and the staff of Rocky Mountain Perinatal Associates will notify you immediately when the results return. If the test predicts a higher than expected risk of chromosomal abnormalities, you may be referred by your obstetrical caregiver to Rocky Mountain Perinatal Associates for further counseling to decide whether or not you would like definitive testing by techniques such as amniocentesis or chorionic villous sampling.
Of all patients who opt to have first trimester screening, approximately 5% will have a result that suggests further testing should be considered (the “screen positive rate”). About 80% to 90% of babies with Down syndrome can be detected using this screening test.
First trimester screening includes first doing an ultrasound measurement of the baby; there is a “clear” are beneath the skin on the back of the baby’s neck (the “nuchal translucency”), that tends to be wider when a baby has Down syndrome. Maternal blood is then drawn by a "finger stick" (like checking a blood sugar level). The maternal blood is evaluated for levels of pregnancy proteins and hormones which tend to be either higher or lower when a baby has a chromosomal abnormality. The ultrasound and blood measurements are then combined to give an estimate of risk.
To avoid inaccurate ultrasound measurements, rigorous training is required before an ultrasound unit is certified to do the nuchal translucency measurement. Currently, Rocky Mountain Perinatal Associates is the only ultrasound unit in Missoula that is certified in performing this test. The test is performed between 11 and 14 weeks gestation. The results usually require 2 to 4 days and the staff of Rocky Mountain Perinatal Associates will notify you immediately when the results return. If the test predicts a higher than expected risk of chromosomal abnormalities, you may be referred by your obstetrical caregiver to Rocky Mountain Perinatal Associates for further counseling to decide whether or not you would like definitive testing by techniques such as amniocentesis or chorionic villous sampling.
Of all patients who opt to have first trimester screening, approximately 5% will have a result that suggests further testing should be considered (the “screen positive rate”). About 80% to 90% of babies with Down syndrome can be detected using this screening test.
