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First Trimester, Fetal genetic Ultrasound and Aneuploidy Screen

Early detection of fetal abnormalities

Before you take any serious measures regarding your healthcare in planning for your pregnancy, make sure to consult with your Obstetrician, your Internist, and with our office. You will be surprised at the relevant available information.

Though the standard in the U.S.A for many years recommended a pregnancy ultrasound at 18 to 20 weeks only for women at high-risk for genetic, obstetrical, or medical complications, this standard is finally changing because of the overwhelming evidence of the value of first trimester evaluations. The discovery of first trimester aneuploidy screen and first trimester genetic ultrasound, has paved the way to earlier detection of fetal syndromes and abnormalities, less invasive testing, earlier parental counseling, and the option for early intervention in both low-risk and high-risk women.

First trimester aneuploidy screen allows for the calculation of risk for the three most common chromosomal abnormalities noted at any maternal age, namely Down syndrome (Trisomy 21 or T21), Trisomy 18 (T18), and Trisomy 13 (T13). This screen requires the combination of some ultrasound derived fetal variables and maternal serum testing for two hormones produced by the placenta, PAPP-A and free Beta hCG. The current ultrasound fetal variables used include the crown-rump length, nuchal translucency (fluid compartment behind the neck), nasal bone, and the presence of tricuspid regurgitation (leaky right heart valve).

The screen is reported as a ratio, for example: Down syndrome risk of 1 in 500, and T18/T13 risk of 1 in 20,000. The screening test does not tell you if a fetus (baby) has or does not have a specific syndrome, but it guides us in determining when to recommend to you an invasive procedure, such as amniocentesis or chorionic villus sampling (CVS), which will then provide a definitive diagnosis of such chromosomal syndromes. A screen is considered “positive” if the calculated risk for Down syndrome exceeds around 1 in 254 (for example it is 1 in 50) or if the risk for T18/13 exceeds around 1 in 150. If all women with “positive” first trimester screen for Down syndrome undergo invasive testing, then 90% of babies with Down syndrome will be diagnosed during pregnancy. It is important to understand that 5 % of all women 35 or older who take the first trimester aneuploidy screen will have a FALSE “Positive” screen therefore this group of women will be subjected to unnecessary emotional upheaval and unnecessary invasive testing.

Once the risks for T21 and T18/T13 are known, the pregnant woman and her partner can make an informed decision regarding invasive testing. Invasive tests, Chorionic Villus Sampling ? (CVS: biopsy of the placenta) or amniocentesis ? are discussed elsewhere.

Only offices certified by the Fetal Medicine Foundation may perform the NT test, and we are proud to be of the few such certified offices in Los Angeles, California.

First trimester genetic ultrasound came about with the advent of high-resolution ultrasound machines, and constitutes the ability to evaluate fetal anatomy around 11 to 13 weeks of the pregnancy. This potential for diagnosing many serious fetal abnormalities in early pregnancy can alleviate the emotional and medical aspects associated with the standard 18 to 20 weeks’ gestation ultrasound. It is important to understand that many genetic and chromosomal conditions are associated with fetal abnormalities therefore if a fetus appears normal on ultrasound, the risks of having any of these conditions is markedly decreased. The key to evaluating the fetus in the first trimester is experience.

Our office has been performing detailed early pregnancy ultrasounds for years and we pride ourselves on being comprehensive in our evaluations. We use a combination of abdominal and vaginal sonography with 2-D and 3-D imaging, and we assess the fetus, the placenta, the umbilical cord, the maternal uterus and ovaries. The evaluation requires an average of 20 to 30 minutes. It is important to note that though many serious fetal abnormalities can be detected in early pregnancy, there are certain abnormalities that cannot be detected until near 18 to 20 weeks of the pregnancy, and others not until after 28 weeks.

How to prepare for, and what to expect during, First Trimester genetic Fetal Ultrasound & Aneuploidy Screen in our office:

  1. You will require 15-20 minutes to fill out paper work in our office prior to your evaluation unless you have filled out the forms on our website including your insurance information
  2. The test is performed between 11 weeks 3 days and 13 weeks 6 days of pregnancy (weeks form first day of last period)
  3. A combination of abdominal and vaginal probe ultrasound is used
  4. Expect mild discomfort during vaginal probe ultrasound
  5. Evaluation does not require a full bladder
  6. The visit averages 45 minutes for one fetus, 1.5 hours for two, and 2 hours for three
  7. A maternal finger stick for blood draw to measure PAPP-A and free Beta hCG which then requires 4-6 days to be processed
  8. CVS or amniocentesis will be recommended if the fetus displays abnormalities or certain findings that suggest an increased risk for chromosomal abnormalities
  9. The absence of fetal abnormalities on ultrasound, a “negative” Aneuploidy Screen, and normal chromosomes, do not delete all possible fetal abnormalities or genetic conditions, and do not guarantee normal organ functioning after birth