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Dr. John Stevens, MD | Consultant Sonologist | Prenatal Diagnosis
Three pictures of sonograms of fetuses.
Services - FASA - Ultra-Screen

FASA sm (Fetal Anatomic Sex Assignment)

Accurate fetal sex determination can be performed by visualization of the external genitalia of the fetus. Fetal Sex Determination by Ultrasound is performed routinely as part of a comprehensive assessment of the fetus and placenta. All of the information usually included in a report for an obstetrician is immediately available to you at the time of your visit. Details of the health and sex of your unborn baby are demonstrated to you during the ultrasound exam. A VHS videotape with the doctor's voice narration can be made at the time of the exam at no extra charge. The VHS video tape is yours to keep as an electronic souvenir.

Seeing the developing fetus may enhance your bond. Knowledge of the sex of the fetus also may further enhance bonding.

Please let us know if you do not want to know the sex of the fetus.

What is FASA sm?
FASA sm stands for Fetal Anatomical Sex Assignment, a procedure developed by Dr. John D. Stephens, M.D., F.A.C.O.G. He has over 26 years experience doing obstetric ultrasound scanning. By using the method he has patented in the U.S., he is able with 100% guaranteed accuracy to tell you the sex (gender) of your unborn fetus from the third month onwards in pregnancy. We currently have obstetrics and sonography offices in Palo Alto, CA and Blaine, WA.

This painless and safe method of ultrasound scanning, which has been over the years approved by both the medical authorities in the U.K. and the United States as totally safe, can help you as the parents of the unborn fetus to bond with your baby. As well as finding out the sex of the baby for you, we do a full health check on the baby to put at rest any fears you might have.


Accuracy of the technique of fetal sex determination by ultrasound (100%) was first established in 1983, when sex predicted by ultrasound was compared to subsequently obtained sex of the chromosomes obtained from genetic amniocentesis ("essentially 100% accuracy" New England Journal of Medicine, October 20, 1983).

  • A new technique, FASA sm permits accurate fetal sex determination of a male and female at 12 weeks at gestation age (GA) (from the first day of the last day of the last menstrual period).
  • 100% accurate.

No harmful effects of real time ultrasound have been shown in ongoing studies in United States, Canada and Europe. Your doctor can explain why an ultrasound examination is recommended.

It is routine recommendation to have an ultrasound examination throughout pregnancy to study the fetus for reassurance. In early pregnancy, ultrasound is used to accurately date the pregnancy, to check for twins and also check the early development for reassurance. At Koala Labs in Palo Alto, CA and Blaine, WA, we perform this examination during 12-14 weeks of GA. There are good reasons for having ultrasound in the first and also second and third trimester.

The external genitalia of the fetus appears to be identical at 10 weeks from the first day of the L.M.P. occurs over the following two weeks. It becomes possible to accurately (100%) determine male and female in the 12th week GA. If the pregnancy is less than 12 weeks from the L.M.P., a repeat FASA sm sonogram may be needed to provide the 100% accuracy.

Those couples that wish to have a FASA sm should have had their appointment based upon having had a prior dating ultrasound study. There are many reasons for having an ultrasound in the first trimester. A prior ultrasound study is highly necessary for those people traveling long distances. This will ensure that your FASA sm study will be performed in the 12-14 weeks G.A. from the L.M.P. (or 10-12 weeks of fetal age development). In this way, Koala Labs can provide you with the assurance of "essentially 100% accuracy" of the fetal sex determination.

Patent Information

  • United States Patent
  • Patent Number: 4,986,274
  • Date of Patent: January 22, 1991
  • Fetal Anatomic Sex Assignment by Ultrasonography During Early Pregnancy
  • Inventor: John D. Stephens
  • Certificate of Grant of Patent UK
  • In accordance with Section 24(2) of the Patents Act, 1977, it is hereby certified that a patent having the specification no. 2166240 has been granted to John D. Stephens, in respect of an invention disclosed in an application for that patent having a date of filing of 16 October 1985 being an invention for "Fetal anatomic sex assignment by ultrasonography during early pregnancy."
  • Dated this Twenty-first day of June 1989 (Mewburn Ellis & Company patent law firm London, UK)

Form for Early Pregnancy Fetal Anatomic Sex Assignment by Ultrasound (F.A.S.A)

Poster for Internation Symposium on First Trimester Fetal Diagnosis


Is Ultra-Screen® a screening test?
Yes. In the field of prenatal testing, screening is especially applicable since the diagnostic tests for Down syndrome and trisomy 18 (Chorionic Villus Sampling or Amniocentesis) can cause pregnancy complications or, in rare cases, a miscarriage. Therefore, it is not practical to provide diagnostic testing to all pregnant women. Instead, the screening test is performed first. The screening test provides the patient with a risk that their pregnancy may be associated with Down syndrome or trisomy 18. If the risk is high, the patient may then decide that they are interested in a more definitive result by undergoing the diagnostic test. It is important to remember, however, that patients with an elevated risk have not been diagnosed as having a pregnancy associated with Down syndrome or trisomy 18. The vast majority of such patients give birth to a healthy child. Patients with a low risk for Down syndrome and trisomy 18 can be reassured about the health of the baby.

What is Ultra-Screen®?
Ultra-Screen® is a first-trimester prenatal screening protocol designed to provide patient specific risk for Down syndrome, trisomy 18 and other chromosomal abnormalities. Ultra-Screen® combines ultrasound measurement of the fluid accumulation behind the neck of the fetus (nuchal translucency) with maternal serum markers and is the earliest and most effective Down syndrome screen available.

How is Ultra-Screen® performed?
Ultra-Screen® consists of a combination of ultrasound exam and a blood test performed between 11 weeks 1 day and 13 weeks 6 days gestational age. The ultrasound demonstrates a fetal heartbeat and determines gestational age, measurement of the length of and by the early fetus called Crown Rump Length (LRL) 45-84. Then, the amount of fluid accumulation behind the neck of the baby, called nuchal translucency (NT), is measured. The blood sample is analyzed for two chemicals called free Beta human chorionic gonadotropin and pregnancy-associated plasma protein-A(PAPP-A), which are normally found in the blood of all pregnant women. The results of the ultrasound exam will be combined with the results of the blood test to estimate a specific risk for Down syndrome and trisomy 18.

Why is Ultra-Screen® so significant?

  • Ultra-Screen® offers 91% detection in the first trimester.
  • Provides you with answers much earlier in pregnancy than all other Down syndrome screening tests.
  • Ultra-Screen® offers earlier reassurance for most patients.
  • Patients who are shown to be at increased risk will have added time to consider if they want to have a diagnostic procedure done, such as amniocentesis or CVS.

What does Ultra-Screen® tell me and my doctor?
Ultra-Screen® can provide helpful information about your pregnancy. In most cases, the test can reassure you that your baby is not likely to be at increased risk for certain chromosomal disorders. In some cases, however, the test can alert you and your doctor that your baby may have one of these disorders. Please remember that if your test result does not fall within normal range, it only means that further testing may be indicated.

How is Ultra-Screen® different from amniocentesis or CVS?
Ultra-Screen® is a non-invasive screening test to determine how likely it is that your baby has Down syndrome or trisomy 18. Amniocentesis and CVS are invasive procedures that determine definitely the presence or absence of Down syndrome, trisomy 18 and other less common birth defects. However, since these procedures are invasive and there is a slight chance they could harm your baby, they are not routinely offered.

How accurate is Ultra-Screen®?
Ultra-Screen® has been extensively studied and is shown to detect about 90% of Down syndrome pregnancies at a 5% false positive rate and 98% of trisomy 18 pregnancies with a 1% false positive rate. In addition, patients carrying babies with other chromosomal disorders or birth defects may have a positive Ultra-Screen®. However, a normal Ultra-Screen® does not eliminate the possibility that the baby may have Down syndrome, trisomy 18 or other chromosomal abnormalities, nor does the test eliminate the possibilities of birth defects, mental retardation and other disorders not detectable by Ultra-Screen®. In the majority of cases, no increased risk is found and patients can be reassured that it is unlikely that their baby has Down syndrome or trisomy 18.

What is Down syndrome?
Down syndrome is a chromosomal disorder that causes physical and mental retardation and birth defects, which may involve the heart and/or digestive tract. The degree of physical and mental retardation for individuals affected by Down syndrome varies greatly. For some, it is minimal; for others, it is substantial. Down syndrome affects approximately one in every 800 babies. Women age 35 and over and those with a previous child with Down syndrome are more likely to have a baby affected with Down syndrome. However, most cases of Down syndrome occur in women under age 35 because they have more babies overall.

What is trisomy 18?
Trisomy 18 is a more severe chromosomal disorder that causes profound mental retardation and multiple birth defects. Few trisomy 18 babies live longer than one year, though some do survive into childhood. Like Down syndrome, the chance to have a pregnancy with trisomy 18 increases with increased maternal age.

What happens if Ultra-Screen® shows that I am at increased risk?
If the Ultra-Screen® test indicates an increased risk for chromosomal abnormalities, you will receive genetic counseling to explain the test results and your options for further testing. These options may include CVS (a test in which a small amount of placental tissue is collected) or amniocentesis (a test in which a small amount of fluid from around the baby is collected) for chromosomal analysis.

Who should be tested?
Screening is recommended for patients under 35 years of age. Women age 35 and over and those with a previous child with Down syndrome are more likely to have a baby affected with Down syndrome; therefore, many physicians offer their patients the opportunity to undergo a diagnostic test (CVS or amniocentesis). However, since these diagnostic tests are associated with a small risk of pregnancy complications or miscarriage, many patients prefer to wait and learn their risk of Down syndrome and trisomy 18 through the Ultra-Screen® test prior to deciding whether to undergo diagnostic testing.

When should the test be done?
The test should be performed between 11 weeks 1 day and 13 weeks 6 days of pregnancy. In some cases, the patient may elect to have the blood test performed at a different time than the ultrasound exam. The blood test can be performed at anytime between 9 weeks 0 days and 13 weeks 6 days.

Early Screening Patient Pamphlet (For California Residents Only)

Visit this site for more information on Determining the Sex of your Baby.

This procedure is the ultrasound exam, which is performed by sonologist Dr. John Stephens in our offices in Palo Alto, CA or Blaine, WA. He will routinely look for the fetal number, the fetal position, any abnormalities of the head, body, spine, limbs, stomach, bladder, for spina bifida and Down syndrome and check the four chambers of the heart. Our sonologist Dr. Stephens will also assess the volume of the amniotic fluid, the location of the placenta, screen the mother’s gallbladder and do any other additional studies, such as external genitalia, that you or your obstetrician may request.


220 California Avenue, Suite 106, Palo Alto, CA 94306
949 3rd Street, Blaine, WA 98230
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