Fetal Medicine

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Information about Fetal Abnormalities

Normally, all cells in the human body have 46 chromosomes, made up of 23 pairs of chromosomes. 23 chromosomes (one of each pair) are inherited from the father and 23 inherited from the mother. These 23 pairs of chromosomes contain all of the DNA, or building blocks, to determine the health of the baby. If, at the time of conception, one extra chromosome is passed on, the baby will have a trisomy (one extra of a particular chromosome). If that extra chromosome is a number 21 chromosome, the baby will have Trisomy 21, more commonly called Down syndrome.

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Choosing The Right Test

Choosing The Right Test

Fetal Anatomy Scan (FAS)

It is recommended that all women are offered a detailed ultrasound scan at about 20 weeks to see if the baby is developing normally. This is known as Fetal Anomaly Scan (FAS).

Why have a Fetal Anomaly Scan?

The vast majority of babies are normal. However all women, whatever their age, have a small chance of delivering a baby with a physical or a mental problem. Many such abnormalities can be diagnosed and ruled out with the Fetal Anomaly Scan. Reasons to have this scan include:

  • To reassure you that your baby is likely to be normal
  • To confirm the gestational age of your pregnancy
  • To confirm the number of fetuses and, if twins, whether they are identical or not
  • To detect birth defects, such as a spina bifida or heart problems
  • If you are concerned about the chances of chromosome problems like Down syndrome, this scan can search for subtle markers that may suggest a higher risk that your baby may have one of these problems
  • If you want to know your baby’s gender this can usually be seen at this scan

When you attend for this scan we will tell you about everything that we see, unless you advise us that there are certain things that you don’t want to know about, such as your baby’s gender or markers for chromosome problems.

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What Can a Fetal Anatomy Scan Detect?

This ultrasound scan is very accurate but unfortunately it cannot diagnose 100% of congenital abnormalities. If the scan is complete, we would expect to pick up at lease 95% of cases of spina bifida, 80% of cases of cleft lip or palate, and 60% to 70% of cases of congenital heart disease.

This scan can also identify 50% to 70% of cases of Down syndrome, but the NIPT test is better for this. Because 30% to 50% of cases of Down syndrome appear normal on ultrasound, only an amniocentesis can give you this information for certain. It is also important to realise that ultrasound scans in pregnancy do not detect problems like cerebral palsy or autism.

Sometimes babies with chromosomal abnormalities have signs called ultrasound markers. These include thick skin in the neck, excess fluid in the kidneys, short arms or legs, white spots in the baby’s heart or abdomen, or choroid plexus cysts in the brain. While some babies with chromosomal abnormalities have these markers, it is important to remember that many normal babies also have these signs.

The only way to diagnose or exclude a chromosomal problem for certain is to have an invasive test, such as amniocentesis. If you would prefer not to know about these markers please inform us prior to the scan. If the scan suggests a problem, you will be told this immediately. You will be able to discuss the findings immediately with a consultant who specialises in fetal medicine.

A full support service will be available for you should any problems be detected, including a referral to an appropriate paediatrician. A copy of your report will be sent to your referring hospital doctor or midwife to ensure good communication.

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Chorionic Villus Sampling (CVS)

The only way to know for sure whether or not your baby may have a chromosomal problem is by having an invasive test, such as Chorionic Villus Sampling (CVS) or amniocentesis (amnio). However, these tests have a small chance of causing a miscarriage of about 1% (about one chance in 100) for CVS, or about 0.1% (about 1 chance in 1000) for amniocentesis.

Choosing the Right Test

CVS is a test which takes a small sample of tissue, the chorionic villi, from your baby’s placenta. The placenta almost always has the same genetic results as the baby. The placenta sample can be tested directly for chromosomal problems, like Down syndrome, or DNA abnormalities, like cystic fibrosis.

Who may be offered CVS?

A CVS is always voluntary and only you can decide if you should have this test. The information below may help you decide whether or not to have this test.  The most common reason to have CVS is for those worried about the chances that the baby may have a chromosomal problem, like Down syndrome. This might include:

  • Women with a NIPT test suggesting an increased chance of having a baby with a chromosomal problem
  • Women who are anxious about the risk of problems, often because of their age
  • Women who have had a previous pregnancy affected by a serious medical problem with the baby

How is the CVS test performed?

CVS is performed in one of two ways, depending on the position of the placenta. A fine needle is passed through the mother’s abdomen and a sample from the placenta is taken. The needle is carefully directed to the right area using ultrasound. Alternatively, a thin plastic straw is passed through the vagina and cervix into the placenta, similar in approach to a cervical smear. Ultrasound is also used to direct the straw to the right area.

When is the CVS test performed?

Ideally the test is performed between 11 to 12 weeks’ gestation. However it may be performed as early as 10 weeks or as late as 14 weeks’ gestation.

What preparation do I need before the test?

A moderately full bladder is preferable. This brings the pregnancy up into the abdominal cavity and therefore easier accessibility for the needle. A scan is first performed to make sure that the baby is alive and of the correct size, to check if there are twins, and to check the position of the placenta. It is possible that you may be asked to empty or re-fill your bladder in order to make sure that your uterus is in the best position.

It is important to know what your blood group is before the test. If possible please ask you doctor or midwife to provide this information to you, or bring along your blood donor card. If you have a negative blood group you will also need to have a special injection of “anti-D” after the CVS test.

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What should I expect after the CVS procedure?

For the first couple of days after the procedure you may experience some abdominal cramping, like period pains, or a little bleeding from the vagina. These are relatively common and in the vast majority of cases are of no importance. You may find it helpful to take painkillers like paracetamol. If there is a lot of pain or bleeding or if you develop a temperature please seek medical advice immediately from your obstetrician or midwife or from the RCSI Fetal  Centre.

When can I expect my results?

The results for Down syndrome and other major chromosomal problems are usually available within 2 weeks. However, if you wish to get your results sooner than this, you can choose to have a portion of the CVS sample sent to a special laboratory that can provide some results in 2 to 3 days. However this rapid test may not be 100% certain of any final diagnosis. It is generally advised to wait until the final results return in 2 – 3 weeks before making final decisions for your pregnancy. The results for other special genetic conditions may take 2 weeks or longer. We will call you with your results as soon as they are available. We will also send a copy to your obstetrician, GP or midwife.

Will the procedure need to be repeated?

In approximately 1% of cases an invasive test will need to be repeated because the test results are inconclusive, or if not enough placenta sample is obtained through the needle. In this situation you will have the option to undergo an amniocentesis test at about 15 weeks’ gestation.

What are the risks associated with the test?

The risk of miscarriage due to CVS is about 0.5% (1 chance in 200) to 1% (1 chance in 100) and this is similar to the risk from amniocentesis at 16 weeks. If a miscarriage is going to occur, you will usually have symptoms within the first 2 to 3 days after the test.

What is the cost of CVS?

There is no cost for CVS if there is a clear medical indication such as a fetal abnormality.  If you have medical insurance, this should cover the cost in other cases.  If there is no indication for CVS, other that maternal anxiety a cost of €250 to €500 may apply.

What if the results are abnormal?

Arrangements will be made for you to receive your results, either by telephone or appointment in the clinic, depending on your preference. Most women who have a CVS will get normal results. However, if the CVS reveals that your baby has an abnormality, we will provide you with full details about what the abnormality means and all the options available to you. You may also have an opportunity to discuss these details with paediatricians or genetic specialists if you and your partner prefer. It is important to remember that you will be offered support, no matter what you decide to do.

It is important to remember that a normal CVS test does not guarantee a normal baby, as it cannot exclude all genetic or fetal abnormalities. It is recommended that you have a Fetal Anomaly Scan at 20 weeks to check for other abnormalities.

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Amniocentesis

What is Amniocentesis?

Amniocentesis is a test in which a small amount of fluid (amniotic fluid) is collected from the pregnancy sac around the baby in the womb. This fluid contains cells from the baby’s skin and bladder which can be grown in the laboratory to test for chromosomal problems, like Down syndrome, or DNA abnormalities, like cystic fibrosis.

Who may be offered Amniocentesis?

Amniocentesis is always voluntary and only you can decide if you should have this test. The information below may help you decide whether or not to have this test. The most common reason to have an amniocentesis is for those worried about the chances that the baby may have a chromosomal problem, like Down syndrome.

How is the Amniocentesis test performed?

Amniocentesis is performed from 16 weeks onwards. Ultrasound is used to carefully direct a very fine needle through the mother’s abdomen, into the womb and then into the amniotic fluid space around the baby. A small amount of this amniotic fluid is then removed. The needle does not touch the baby. The fetal heart rate is checked both before and after the test. Local anaesthetic is not required as the needle is so thin.

What preparation do I need before the test?

No special preparation is needed before the test. Your bladder does not need to be full. A scan is first performed to confirm the baby’s size and the position of the placenta. It is very important to inform the medical staff if you are taking medication such as “blood thinning” agents (Heparin or Aspirin) that may need to be stopped prior to your procedure. It is important to know what your blood group is before the test. If possible please ask your doctor or midwife to provide this information to you, or bring along your blood donor card. If you have a negative blood group you will also need to have a special injection of “anti-D” after the amniocentesis.

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What should I expect after the Amniocentesis?

For the first couple of days after the procedure you may experience some abdominal cramping, like period pains. This is relatively common and in the vast majority of cases is of no importance. You may find it helpful to take painkillers like paracetemol. If there is a lot of pain or bleeding or if you develop a temperature, please seek medical advice immediately from your obstetrician, midwife, or from the RCSI Fetal Centre.

When can I expect my results?

The results for Down syndrome and other major chromosomal problems are usually available within 2-3 weeks. However, if you wish to get your results sooner than this, you can choose to have some of the amniotic fluid sample sent to a special laboratory that can provide some results in 2-3 days. However, tnis rapid test may not 100% certain of the final diagnosis. The results for other special genetic conditions may take 2 weeks or longer. We will call you with your results as soon as they are available.

What if the results are abnormal?

Arrangements will be made for you to receive your results, either by telephone or appointment in the clinic, depending on your preference. Most women who have an amniocentesis will get normal results. However, if the amniocentesis reveals that your baby has an abnormality, we will provide you with full details about what the abnormality means and all the options available to you. You may also have an opportunity to discuss these details with paediatricians or genetic specialists if you and your partner prefer. It is important to remember that you will be offered support, no matter what you decide to do.

Choosing The Right Test