What is nuchal translucency?

This is a collection of fluid under the skin at the back of a baby's neck at 10-14 weeks that can be measured using ultrasound. All babies have some fluid, but in many babies with Down's syndrome, the nuchal translucency (NT) is increased.

An NT scan is a method of assessing whether your baby is likely to have Down's syndrome. It's a screening test. A screening test can only estimate the risk of your baby having Down's, as opposed to a diagnostic test, such as CVS or amniocentesis, which will give you a definite diagnosis (but also carries a small risk of miscarriage).

The NT scan can't tell for certain whether your baby is affected. However, it can help you decide whether or not to have a diagnostic test.

When can I have the test?

NT scans are usually performed from 11 to 13 weeks + 6 days of pregnancy. Before 11 weeks the scan is technically difficult because the baby is so tiny and, after 14 weeks, excess fluid may be absorbed by the baby's developing lymphatic system.

How is it done?

The main part of the test involves an ultrasound scan. The scan is usually done through your tummy, but depending on the position of your baby and your womb, sometimes it's necessary to perform a vaginal scan, which will give better views. There is no risk to you or your baby and it should not be too uncomfortable.

To accurately date your pregnancy, the sonographer will measure your baby from the top of its head to the bottom of the spine. She will then measure the width of the NT. The skin will appear as a white line, and the fluid under the skin will look black. Your baby fits nicely on the screen at this stage, and you will be able to see the head and spine, limbs, hands and feet. Some major abnormalities may be excluded at this scan, but it's recommended you also have a detailed scan at 20 weeks.

It's a good idea to take your partner or a friend with you, to share the experience and be with you when you get the result.

What is a normal measurement?

An NT measurement of up to 2.0mm is normal at about 11 weeks, and up to about 2.8mm by 13 weeks and 6 days. This is because the NT normally grows in proportion to the growth of the baby. Image 1 shows a baby with a normal NT of 1.3mm; this baby will be low risk.

1. Normal nuchal translucency 

If the NT is increased, it does not mean there is definitely a problem. Some normal babies have increased fluid, too. Image 2 shows a baby with an NT of 2.9mm, which is at the upper limit of the normal range. Though the risk will be higher than the baby's in the first image, nine out of 10 babies with a measurement between 2.5mm and 3.5mm will be completely normal.

2. Borderline nuchal translucency

As the NT increases, so does the risk. The baby in image 3 has an NT of 6mm and will be very high risk for Down's, as well as other chromosomal and genetic syndromes and heart problems. Fortunately, not many babies have as much fluid as this.

3. Increased nuchal translucency

How is the risk calculated?

Every woman has a risk of giving birth to a baby with Down's syndrome, and this risk increases with age. First the database will show you the risk that applies to all women of your age, known as the background risk. Then, using the measurements from the scan, a new risk will be generated which is your own individual risk for this pregnancy. This may be higher or lower than your background risk.

When will I get the results?

The results should be available immediately.

What do the results mean?

The results will express the probability of your baby having Down's syndrome.

Low risk is a result where the risk is less than one in 300. On your results print-out this will be expressed as a ratio, for example, 1:800. This means that out of 800 women who have this risk, one will have a baby with Down's syndrome.

High risk is a result where the risk is greater than one in 300, for example, 1:150. This means that out of every 150 women who have this risk, one will have a baby with Down's syndrome.

Make sure that you thoroughly understand the information that the specialist gives you. Ask her to go through things again if you don't understand. If you would like to know more about Down's syndrome, contact the Down's Syndrome Association.

What should I do if I am high-risk?

About one in 20 women will be given a high risk, and the vast majority go on to have a normal baby. Even with a risk as high as 1:5, the baby has four out of five chances that he does NOT have Down's. Nevertheless, once your pregnancy has been labelled high-risk, you will probably feel anxious and perhaps unsure of what to do.

The only way to know for certain if your baby has Down's or another chromosomal abnormality is to have a diagnostic test such as CVS or amniocentesis. This decision can be very difficult, but you do not have to decide in a hurry. One advantage of the NT scan is that it is done early in your pregnancy, and it is possible to have a CVS and get the result while you are still in the first trimester. If you are unsure what to do, you can wait until 16 weeks and have an amniocentesis then if you wish. Your midwife or doctor will provide more information if you need it.

How reliable is a nuchal translucency scan?

A large research study involving over 100,000 pregnancies found that about 75 per cent of babies with Down's syndrome were correctly identified using this method. When combined with a blood test, the detection rate improves to about 90 per cent. However, to achieve these detection rates, it is important that the NT is measured accurately. For this reason, strict standards have been devised so that every sonographer measures in exactly the same way. To use the database to calculate the risk, sonographers must first undergo training by the Fetal Medicine Foundation and, once they are considered competent, their technique and results are reviewed every year.

At Woman And Fetal Imaging WAFI, we look forward to sharing this unforgettable experience with you. We know that your visit with us will be a memory that lasts a lifetime and you'll love the family bonding experience!

What is 3D/4D Ultrasound?

your baby in three-dimensional view. You can actually see your baby’s facial expressions. Maybe he/she is sucking his/her thumb or clasping his/her tiny hands. Who is the baby starting to look like … you or your husband or maybe even the grandparents? Seeing this “realistic” image before birth allows you a unique privilege to connect with your unborn child. 3D/4D ultrasound is to 2D ultrasound what video and DVD are to a still photograph.

We purchased the new GE 3D/4D ultrasound technology. The 4D technology provides us with the ability to view 3D images in real-time. The baby can be seen moving in three dimensions. You will be impressed! This sophisticated system is the only one on the market with this capability.

In addition to the 4D images of the fetus, we will also have a detailed look at the internal anatomy of the baby with advanced 2D scanning to check for abnormalities and assess fetal growth and well-being. The same probe that takes 4D images can be used to provide advanced 2D images and blood flow measurement (Doppler). Additional important information that will be
provided at the various stages of pregnancy is summarised below.

11-14 weeks

Measuring the fetus from 'top to bottom' (crown-rump length (CRL)) will provide an accurate assessment of the gestational age and will provide an estimated date of delivery.

In addition we will carry out a screening for Down syndrome by:

Combining the nuchal scan and the blood test, we will give an individual risk assessment (likelihood ratio) for your risk of having a Down Syndrome baby. We can compare your 'starting' risk, based on your age, with the 'new' risk, which will help you decide whether you want an invasive test such as CVS or Amniocentesis. If the risk of Down's is 1:250 or greater, an invasive test is advised.

The combination of these should give an 85% detection rate for Down Syndrome. Other recent markers for Down Syndrome, such as nasal bone identification and blood flow in the Ductus Venosus, may also be performed depending on the particular clinical circumstances.

18-22 weeks

As this stage, a detailed scan is performed which will detect the large majority of serious fetal anatomical abnormalities. Detailed scanning of the baby's brain, spine, heart, diaphragm, kidneys, bladder, genitalia, limbs, fingers & toes can be seen in some detail with ultrasound.

Also at this time, blood flow in the uterine arteries is measured using Doppler ultrasound. This can predict whether the placenta will function normally or (if blood flow is impaired) whether the baby's growth will be affected or high blood pressure will develop in the mother (pre-eclampsia).

In women at risk of premature labour, the length of the cervix can be measured using transvaginal ultrasound (an internal scan): a short cervix indicates an increased risk of early delivery.

Scan 26 weeks onwards

An assessment of baby's growth and anatomy will be performed at the time of the 4D scan. Measurements of the fetal head, body and upper leg (femur) will be plotted on a graph to show the rate of growth of the baby. Blood flow in the baby's Umbilical Cord and mother's Uterine Arteries will indicate if the placenta is functioning normally. If placental blood flow is normal then an estimated prediction of the likely birth weight can be given.

What is Doppler?

Doppler is a form of ultrasound which measures the speed of red blood cells moving along blood vessels. It takes two principal forms, one, where a colour map of the blood vessels is shown on the conventional ultrasound image (colour Doppler); another where a tracing of the flow is shown on a graph so that the speed of flow can be measured (spectral Doppler). You do not need a separate examination for Doppler; it is done at the same time as the usual ultrasound examination.

Why is Doppler useful?

Blood flow is important because it is the method by which oxygen is transported to body organs and therefore improves the function of these organs. We can measure blood flow to the uterus and to the ovaries. During a women's fertile years there is a fluctuation of blood flow during the menstrual cycle with more blood flow to the uterus in the second half of the cycle to aid implantation of the embryo. An increase in blood flow is also found before ovulation around healthy follicles which gives an indication of the health of the oocytes (eggs).

After the menopause blood flow to the uterus decreases due to the fall of oestrogen and when this occurs the effectiveness of hormone replacement therapy can be monitored by measuring the increase in blood flow.

Are there abnormalities in blood flow with specific conditions?

Yes, in polycystic ovary syndrome there is usually an increase in blood flow in the central part of the ovary (stroma) which reflects the local disturbance in growth hormones. Also the blood flow to the uterus is frequently poor which may explain the high miscarriage rate with this condition. With uterine fibroids there is usually an increase in blood flow and the higher the flow the greater the chance of fibroids growing. With ovarian cysts, a high internal flow indicates an increased risk of malignancy.

1. Amniocentesis

Inside the uterus, amniotic fluid surrounds and protects your baby. The main source of amniotic fluid is fetal urine. By analyzing a small sample of amniotic fluid, we can learn many things. For example, amniotic fluid studies can detect conditions such as Down syndrome, trisomy 18, trisomy 13 and other genetic abnormalities. Your doctor and genetic counselor will explain the conditions that can and cannot be detected using amniotic fluid.

Amniotic fluid is removed from the uterus by a procedure called amniocentesis. Your doctor will use ultrasound to identify an appropriate pocket of amniotic fluid inside the uterus. Then, under sterile conditions, a very fine needle will be inserted into the amniotic fluid and about 20 ml (4 teaspoons) of amniotic fluid will be removed with a syringe. The needle is then removed. The procedure usually lasts about 30 seconds and your doctor will use ultrasound throughout the procedure to ensure safety. The amniotic fluid is then sent to the lab for testing. In most cases, you will be able to resume your normal activities the next day. The 20 ml of amniotic fluid that are removed account for no more than 2-4% of the total fluid in the uterus and your baby will replenish it within a day. If your blood type is Rh negative, we will recommend that you have a RhoGam injection before leaving the office.

Bleeding, infection and miscarriage are uncommon after amniocentesis. The rate of miscarriage is less than 1%.

2. Chorionic Villus Sampling

Chorionic villus sampling (CVS) is a prenatal test that involves taking a small sample of tissue from the placenta, a structure in the uterus that provides blood and nutrients from the mother to the fetus, to test for chromosome abnormalities, such as Down syndrome and many others, and certain other genetic problems. Before having the test done, your genetic counselor and doctor will explain the conditions that can and cannot be detected using CVS tissue.

The chorionic villi are tiny projections of placental tissue that look like fingers and contain the same genetic material as the fetus. Testing may be available for other genetic disorders, depending on the family history and availability of lab testing at the time of the procedure.

CVS is usually performed at about 11 weeks of pregnancy. Unlike amniocentesis (another type of prenatal test), CVS does not provide information on neural tube defects, such as spina bifida. For this reason, women who undergo CVS also need a follow-up blood test called a maternal serum alpha-fetoprotein (AFP) level between 16 to 18 weeks of their pregnancy to screen for neural tube defects. It is also a good idea for them to have a detailed ultrasound at about 18 weeks to look at the spine of the fetus in particular for the same reason.

In our center, transcervical CVS is performed. This is a procedure in which a catheter is inserted through the cervix into the placenta to obtain the tissue sample. Removing the small amount of tissue does not affect the fetus’s ability to get the blood supply it needs from the placenta.

Bleeding, infection and miscarriage are uncommon after CVS. The rate of miscarriage is less than two percent.

3. Percutaneous Umbilical Blood Sampling (PUBS)

For certain tests, it may be necessary to obtain a small sample of blood from your baby’s umbilical cord. In other conditions, such as severe anemia, your baby might actually need a blood transfusion while still inside the uterus. When these things are necessary, they are done by a procedure called Percutaneous Umbilical Blood Sampling (PUBS). Before the procedure, the indications, risks, benefits and alternatives will be explained to you in detail. The procedure is performed in the hospital under sterile conditions. Your doctor will use ultrasound to identify the umbilical vein within the umbilical cord. Under ultrasound guidance, a thin needle will be inserted into the umbilical vein. Blood will be drawn and/or transfused as needed. In some cases, medications may be administered into the umbilical vein.

4. Intrauterine fetal blood transfusion

Treatment Overview

An intrauterine transfusion provides blood to an Rh-positive fetus when fetal red blood cells are being destroyed by Rh antibodies.

A blood transfusion is given to replace fetal red blood cells that are being destroyed by the Rh-sensitized mother's immune system. This treatment is meant to keep the fetus healthy until he or she is mature enough to be delivered.

Transfusions can be given through the fetal abdomen or, more commonly, by delivering the blood into the umbilical vein. Umbilical cord vessel transfusion is the preferred method because it permits better absorption of blood and has a higher survival rate than does transfusion through the abdomen.¹

An intrauterine fetal blood transfusion is done in the hospital. The mother may have to stay overnight after the procedure.

• The mother is sedated, and an ultrasound image is obtained to determine the position of the fetus and placenta.
• After the mother's abdomen is cleaned with an antiseptic solution, she is given a local anesthetic injection to numb the abdominal area where the transfusion needle will be inserted.
• Medication may be given to the fetus to temporarily stop fetal movement.
• Ultrasound is used to guide the needle through the mother's abdomen into the fetus's abdomen or an umbilical cord vein.
• A compatible blood type (usually type O, Rh-negative) is delivered into the fetus's abdominal cavity or into an umbilical cord blood vessel.
• The mother is usually given antibiotics to prevent infection. She may also be given tocolytic medication to prevent labor from beginning, though this is unusual.

What To Expect After Treatment

A short recovery period (approximately 1 to 3 hours) is necessary to allow the mother's sedatives to wear off. If the fetus was given medication to prevent movement, it may be several hours until the mother can feel the fetus moving again.

Why It Is Done

A sensitized mother's immune system can destroy a large proportion of fetal red blood cells, causing severe anemia. Intrauterine blood transfusions are done when:

• Doppler ultrasound of the middle cerebral artery suggests anemia.
• The bilirubin result from amniocentesis testing shows that the fetus is moderately to severely affected by Rh sensitization.
• Ultrasound shows evidence of fetal hydrops, such as swollen tissues and organs.
• Fetal blood sampling (FBS) shows that the fetus has severe anemia. The transfusion may be done immediately.

In a severely affected fetus, transfusions are done every 1 to 4 weeks until the fetus is mature enough to be delivered safely. Amniocentesis may be done to determine the maturity of the fetus's lungs before delivery is scheduled.

How Well It Works

Fetal survival after transfusion depends upon the severity of the fetus's illness, the method of transfusion, and the skill of the doctor who does the procedure. Overall, after intravascular transfusion:²

• More than 90% of fetuses that do not have hydrops survive.
• About 75% of fetuses that have hydrops survive.

Risks

Intrauterine transfusions may cause:

• Uterine infection.
• Fetal infection.
• Preterm labor.
• Excessive bleeding and mixing of fetal and maternal blood.
• Amniotic fluid leakage from the uterus.
• Fetal death.