First-Trimester Screening: Frequently Asked Questions

First-trimester risk assessment is available to all women whose pregnancies are between 11 and 14 weeks' gestation.

Since any baby--even the child of younger parents--has a small risk of being born with Down syndrome, it is suggested that all mothers-to-be consider evaluation. As a woman becomes older, it may help her decide whether to proceed with diagnostic testing later in pregnancy, such as amniocentesis or chorionic villus sampling (CVS).


We use a safe, non-invasive method involving blood analysis and ultrasound. Using a highly accurate computer algorithm, we combine the results of these tests to determine the statistical likelihood of your baby having chromosomal abnormalities.


The screening helps identify babies who may have Down syndrome or trisomy 18, a very serious genetic disorder.


Between weeks 11 and 14 after your last menstrual period. It is important to speak with your obstetrician or call us as soon as you learn you are pregnant to schedule an appointment during this very specific timeframe. In order to receive immediate results at the time of your risk assessment, you must have your blood drawn at least one week before your scheduled appointment.


You may have your blood drawn at either Yale Lab Medicine or Quest Diagnostic Laboratories. Please visit these websites to find the location nearest you. Please ask your obstetrician or Yale Maternal-Fetal Medicine to complete a blood request form before you go.


Alternatively, you could have your blood drawn at the time of your risk assessment appointment. However, this requires waiting approximately one week after your appointment to receive your baby's risk assessment from your obstetrician's office.


Yale Maternal-Fetal Medicine is comprised of 10 perinatologists at the cutting edge of clinical management and research in high-risk obstetrics.

  • Yale MFM physicians were co-authors of the first USA study for First Risk Assessment.
  • In 2000, Yale Maternal-Fetal Medicine and the Yale Genetics offered New England's first comprehensive First-Trimester Risk Assessment program.
  • Accurate measurements require standardized ultrasound scanning. The risk prediction is very dependent on careful measurement of this space. Therefore, the most accurate results are obtained when individuals who have special training and certification in this particular technique perform the ultrasound.

We are not only leaders in our field, but are also pioneers. Yale Ob/Gyn:

  • has the first comprehensive First-Trimester Risk Assessment program in New England
  • co-authored the first U.S. study for first-trimester risk assessment
  • developed first fetal monitoring
  • invented first fetal echocardioriaphy
  • pioneered first obstetrical ultrasound
  • developed first fetal blood sampling and first fetal transfusion
  • offered first chorionic villus sampling (CVS) in New England
  • invented fetal monitoring and many prenatal diagnostic and treatment techniques

A specially certified sonographer conducts an ultrasound examination to measure a characteristic called nuchal translucency (NT) at the back of the baby's neck. This procedure takes about 20 minutes.

Simple blood tests are used to detect the presence of certain proteins and hormones in your blood. The results of the ultrasound and blood tests are combined to provide a personalized estimate of your risk of having a baby with Down syndrome or trisomy 18.

When you have your blood drawn before your screening appointment, you will receive your baby's risk assessment immediately after the ultrasound exam. If you choose to have your blood drawn at the time of your screening appointment, you will have to wait approximately one week for the results. They will come to you through your obstetrician's office.


A baby with Down syndrome or another chromosome abnormality can be born to any couple. Almost always, the egg or sperm that started the baby's life is abnormal, although it is not known why this happens to some couples and not others. The chances of having a baby with chromosomal abnormalities increase with the mother's age.

About Down syndrome: this genetic disorder results in varying degrees of physical and mental retardation. Developmental problems range from mild to severe. The most common chromosomal disorder, Down syndrome affects about 1 in 800 infants.

About trisomy 18: this is a more severe chromosomal disorder. Trisomy 18 babies are typically born with multiple birth defects and profound retardation. Most do not live beyond one year.

Maternal age at due date

Risk of having a live-born with Down Syndrome

Risk of having a live-born with any chromosome abnormality*








































* including Down syndrome


No. Currently only Down syndrome and trisomy 18 can be detected by screening through measurements of proteins in the mother's blood and nuchal translucency. If the fetus's NT measurement is greater than 3 mm, which occurs in fewer than 1-in-20 women (5%) there may be an increased risk of some types of birth defects. If this is the case, we will discuss the implications with you in detail. First-trimester risk assessment is not a substitute for a careful examination of your baby with ultrasound later in pregnancy to check for structural problems.


The procedure is non-invasive and therefore very safe. Because the assessment can be done without the risks of a needle puncture to remove amniotic fluid with amniocentesis, and because the results can be obtained weeks before amniocentesis (16-17 weeks), many of the fears associated with prenatal genetic testing can be alleviated.


First-trimester risk assessment can detect approximately 90% of babies with Down syndrome. This means that if a baby has Down syndrome, there is a 10% chance that the abnormality will not be detected by first-trimester risk assessment. Of all the women who have first-trimester risk assessment, 5% will have a positive first-trimester risk assessment result. This does not mean that the baby has Down syndrome. Most women with a screen positive result have healthy babies. Only further tests (CVS or amniocentesis) can diagnostically detect Down syndrome.


First-trimester risk assessment risks that are less than 1 in 270 are considered 'low risk' and do not require further evaluation and testing. Approximately 95% of pregnant women tested will have a 'low risk' result. Since this is a screening test, there is still a small chance that the fetus may be affected, even when the screening test is negative.

Pregnancies in which the risk of Down syndrome is higher than 1 in 270 (0.5%) are considered 'high risk'. In some circumstances there may also be an increased risk of a heart defect or other birth defects. Approximately 5% of all pregnancies tested will have results equal to or greater than 1 in 270; in those cases, prenatal diagnostic testing, such as chorionic villi sampling (CVS) or amniocentesis may be considered.

Please remember, this is a screening test utilized only to estimate the risk of Down syndrome. It is not a diagnostic test. A 'high-risk' result does not mean that the fetus has Down syndrome just as a 'low risk' result does not guarantee the fetus will not be affected. However, the risk assessment resulting from the screening test is the most accurate non-invasive procedure currently available.


Your obstetrician will provide routine, standard care. First-trimester risk assessment is a screening test to identify the risk for Down syndrome; this test does not assess the risk of open fetal spinal defect (neural tube defect or spina bifida). Therefore, a second blood test measuring serum alpha-fetoprotein (AFP), done between 15 and 19 weeks of pregnancy, is recommended to evaluate this risk.


No. A 'high risk' test does not mean that the fetus has Down syndrome or any other problem. Rather, a 'high risk' test results mean that further evaluation of the pregnancy will be offered to rule out such problems. Most women with 'high risk' results have normal follow-up tests and healthy babies.


If the calculated risk of Down syndrome is greater than or equal to 1 in 270, the following options are available:

  1. Diagnostic testing by chorionic villus sampling (if your pregnancy is between 11 and 13 weeks' gestation); or
  2. Diagnostic testing by routine amniocentesis (if your pregnancy has passed the 15 week mark); or
  3. No further testing or evaluation may be desired.

A Yale genetic counselor will be available to answer all questions to help in making decisions about further testing.


Information comparing results from first- and second-trimester screening tests is still being collected. Although first-trimester screening has been shown to be a more accurate assessment of risk for Down syndrome, some doctors believe that having both first and second trimester testing provides a more thorough screening in pregnancy. Until further information is available, it is recommended that you discuss second-trimester multiple-marker screening with your primary care ObGyn.


If you have your blood drawn one week prior to your scheduled appointments, results are immediate. If you choose to have your blood drawn at the time of your risk assessment appointment, your obstetrician's office will call you within a week with results.


Unlike these procedures, first-trimester risk assessment is non-invasive and completely safe. This is reassuring for you if you are worried about the risks associated with other prenatal genetic testing. Also, first-trimester risk assessment can be performed early, between 11-14 weeks' gestation (i.e., between 11-14 weeks after your last menstrual period). Although they are invasive procedures, amniocentesis and CVS are useful in offering precise detection of Down syndrome, trisomy 18 and other birth defects.


Our screening methodology has been extensively studied and is proven to detect about 90% of babies with Down syndrome or trisomy 18.

However, a normal risk assessment does not eliminate the possibility that your baby may have Down syndrome, trisomy 18 or other abnormalities. In most cases, a low risk is found and parents feel an increased sense of reassurance.


If you are pregnant and in your first trimester, ask your obstetrician how you can get your immediate first-trimester risk assessment at Yale, or call us today at (203) 785-5682 to schedule an appointment.