Services

Prenatal genetic screening & nuchal translucency ultrasound

Prenatal Genetic Screening is a test that evaluates a woman’s chance of having a child that may be at “high risk” for having a chromosomal abnormality such as Down syndrome, trisomy 18, or an open neural tube defect. Maternal blood tests & nuchal translucency ultrasound are two available screening tools that can be used independently, or in combination to provide a numerical risk estimate of your pregnancy being affected by one of these conditions. Which tests are available as public funded service or a private pay option depends on your age, how far along you are in your pregnancy, whether you are having twins or triplets, and your previous pregnancy history. All women have a small chance of having an affected child. Prenatal screening can provide further clarification of what your independent risk is.

Tell me more about the available prenatal blood tests or serum screening.

The blood tests are performed on the mother, and therefore pose no risk to the pregnancy. They measure the levels of specific proteins in the mother’s blood that are made by the baby and/or the placenta. The normal pattern of these proteins is known. In pregnancies affected by Down syndrome, trisomy 18 and neural tube defects, the levels of these proteins can be different. These protein levels are taken into account when calculating your risk estimate of having an affected child in this pregnancy. A number of blood tests are available and are done in the first and second trimester.

What is a nuchal translucency?

A nuchal translucency (NT) is an ultrasound measurement of the fluid at the back of a baby’s neck between 11 and 13+6 weeks of pregnancy. It is a screening test to determine if your baby is at an increased or decreased risk of certain abnormalities. All babies have some fluid collection behind the neck, but babies with Down syndrome & trisomy 18, tend to have an unusually high amount. An increased nuchal translucency and an absent nasal bone in the first trimester is seen in 70% of babies with Down syndrome. Therefore, an NT can provide valuable insight early in pregnancy. In addition, the results from your serum screening can be factored in with your nuchal translucency when calculating your overall risk assessment. Adding an NT to blood tests reduces the chances of making an error called a “false positive” where the tests indicate a positive screen when in fact everything is normal. This early ultrasound can also confirm the gestational age and provide some reassurance as to how your baby is developing. It is important to note that this ultrasound does not replace the recommended ultrasound at 18-20 weeks because many organ systems are not fully developed at this early gestational period.

Within British Columbia’s public healthcare system, all women can have prenatal genetic screening to assess their risk of having a baby affected by Down syndrome, trisomy 18, and open neural tube defects if they wish to pay privately. The province will funds NT ultrasounds for:

• women over 36 years of age
• women with a previous child/pregnancy with down syndrome, trisomy 18, or trisomy 13
• women over 35 who have had 3 previous miscarriages
• women carrying twins or triplets at any maternal age
• HIV positive women.

Who performs nuchal translucency at The Kelowna Regional Fertility Centre?

NT’s are performed by a Fetal Medicine Foundation (FMF) certified ultrasonographer under the supervision of Dr. Kathy Wise, M.D., F.R.C.S. Dr. Wise is an Obstetrician/Gynecologist who has successful completed the Nuchal Translucency Theory Course and Quality Assurance Program and oversees our FMF certified ultrasonographer.

What options are available at The Kelowna Regional Fertility Centre for prenatal genetic screening?

There are two options available at our clinic for women who wish to have a nuchal translucency ultrasound as part of their prenatal genetic screening. Screening tests combine the measurements from the ultrasound with results from at least one blood test.

1. First Trimester Screening (nuchal translucency with private pay blood work)
2. Nuchal translucency with provincially funded blood work

First Trimester Screening (FTS)

FTS consists of a nuchal translucency ultrasound measurement combined with a blood test (PAPP-A and free beta-hCG) both of which are performed between 11 and 13 + 6 weeks gestation. The results will provide a numerical risk estimate of the chance of Down syndrome and trisomy 18.

Advantages

The main advantage of FTS is related to the speed of the results. Because testing is done in the first trimester, FTS can provide women with reassurance regarding their baby’s health much earlier in the pregnancy (as early as 12 weeks gestation). In the event of worrisome results, FTS allows for earlier diagnostic testing and decision making. FTS has the ability to detect 85-90 % of babies with Down syndrome or Trisomy 18.

Disadvantages

The main disadvantage is that FTS is slightly less accurate than an NT with provincially funded blood work as the chance of a false positive is slightly higher. This means that with FTS, approximately 2% more babies will be detected as abnormal who are actually normal.

How do I get my results?

Your test results will be available within 5-7 days of your scan and a letter will be sent to your referring physician. You will also be contacted by our staff directly to notify you of the results. Results are categorized as either screen positive or screen negative. If you are “screen positive”, you will be offered a follow up in person to discuss what the results mean and what your options are for further testing.

Nuchal translucency with provincially funded blood work

This screening test combines measurements from a nuchal translucency ultrasound with two separate provincially funded blood tests to estimate the chances of a developing baby having Down syndrome, trisomy 18 or an open neural tube defect. The first blood test is done between 10 and 13+6 weeks, the NT ultrasound between 11 and 13+6 weeks and the second blood test between 15 and 20+6 weeks gestation. The bloodwork is arranged by your primary obstetrical caregiver and is done at a provincially funded external lab.

Advantages

Results offer a slightly higher detection rate (up to 95%), and slightly lower false positive rate (<5%) than a FTS assessment, meaning that fewer women will be offered an unnecessary amniocentesis which carries a 1 in 200 (1:200) risk of miscarriage. To further clarify, for every 200 women that have an amniocentesis, one will miscarry as a direct result of the test. In addition, the blood work also includes a screen for open neural tube defect as part of the second blood test.

Disadvantages

The main disadvantage is related to the delay in obtaining results. Results are not available until 10 days after the second blood test. The earliest that results may be available is 16 ½ weeks if the second blood test is done right at 15 weeks. This can delay decision making about further testing options and thus diagnosis.

How do I get results?

Your results will be available within 10 days of having your second blood test. These results will be sent to the family physician, midwife, or obstetrician that will be following you through your pregnancy. As with FTS, the results are categorized as either screen positive or screen negative.

What will my visit to the Kelowna Regional Fertility Centre be like?

When you arrive at the clinic, you will be asked to fill out a short history form about your medical and pregnancy history. In addition, you will have an orientation session with one of our nurses where you will have opportunity to ask any questions that you may have. If you are having a FTS, your blood test will be done at the clinic. Please try to arrive with a comfortably full bladder in preparation for the NT ultrasound.

What is the cost?

Please refer to The Kelowna Regional Fertility Centre’s current fee schedule.

For further information about the BC Prenatal Genetic Screening Program visit www.bcprenatalscreening.ca