• Amniocentesis involves the examination of cells in the fluid from around the fetus (amniotic fluid).
• The cells in the amniotic fluid originate from the baby and so the chromosomes present in these cells are the same as those of the baby.

How is amniocentesis done?

• Amniocentesis involves passing a thin needle into the uterus in order to remove a small volume of amniotic fluid. The needle is carefully observed using ultrasound scan.
• The fluid is fetal urine and the amount removed by amniocentesis reaccumulates within a few hours.
• The procedure lasts 1 minute and afterwards we check that the fetal heart beat is normal.

What should I expect after amniocentesis?

• For the first couple of days you may experience some abdominal discomfort or period-like pain. You may find it helpful to take simple painkillers like paracetamol.
• If there is a lot of pain, bleeding, loss of fluid from your vagina or if you develop a temperature please seek medical advice.

When can I expect to get the results?

• The results for Down's syndrome and other major chromosomal defects are usually available within 3 days. The results for rare defects take 2 weeks. As soon as we get the results, we will call you to let you know.

What are the risks associated with amniocentesis?

• The risk of miscarriage due to amniocentesis is about 1% and this is the same as the risk from chorion villus sampling. If you were to miscarry due to the test, this would happen within the next five days.
• Some studies have shown that when amniocentesis is performed before 16 weeks there is a small risk of the baby developing club feet. To avoid this risk we never perform amniocentesis before 16 weeks.

• Chorion villus sampling (CVS) involves the examination of chorionic villi (placental tissue). Both the baby and placenta (afterbirth) originate from the same cell and so the chromosomes present in the cells of the placenta are the same as those of the baby.

How is CVS done?

• Local anaesthetic is given. A fine needle is then passed through the mother's abdomen and a sample of villi is taken. The needle is carefully observed using ultrasound scan.
• The procedure lasts 1 minute and afterwards we check that the fetal heart beat is normal.

What should I expect after the CVS?

• For the first couple of days you may experience some abdominal discomfort, period-like pain or a little bleeding. These are relatively common and in the vast majority of cases the pregnancy continues without any problems. You may find it helpful to take simple painkillers like paracetamol.
• If there is a lot of pain or bleeding or if you develop a temperature please seek medical advice.

When can I expect to get the results?

• The results for Down's syndrome and other major chromosomal defects are usually available within 3 days. The results for rare defects take 2 weeks. As soon as we get the results, we will call you to let you know.

Will the procedure need to be repeated?

• In approximately 1% of cases the invasive test will need to be repeated because the results are inconclusive.

What are the risks associated with the test?

• The risk of miscarriage due to CVS is about 1% and this is the same as the risk from amniocentesis at 16 weeks. If you were to miscarry due to the test, this would happen within the next five days.
• Some studies have shown that when CVS is performed before 10 weeks there is a small risk of abnormality in the baby's fingers and/or toes. To avoid this risk we never perform CVS before 11 weeks.

Some obstetricians advise that this scan is offered to all women. Others reserve such scans for those women who have had previous complications of pregnancy such as pre-eclampsia, growth restriction, diabetes, stillbirth, and for those women who develop a problem during the course of their current pregnancy.

This scan aims to determine the growth and health of the fetus by:

• Measurement of the size of the fetal head, abdomen and thigh bone and calculation of an estimate of fetal weight
• Examination of the movements of the fetus
• Evaluation of the placental position and appearance
• Measurement of the amount of amniotic fluid
• Assessment of blood flow to the placenta and fetus by colour Doppler ultrasound

This scan is especially recommended for women with a family history of heart abnormalities, or where increased nuchal translucency had been found at the 12 week scan. It is also an important scan in assessing the risk for Down's syndrome because many of these babies have heart abnormalities.

During the scan we examine each part of the fetal body, determine the position of the placenta, assess the amount of amniotic fluid, and measure fetal growth. Special attention is paid to the brain, face, spine, heart, stomach, bowel, kidneys and limbs.

In women at high risk for preterm delivery (multiple pregnancies, previous preterm birth, abnormalities of the uterus or previous cervical surgery) we also carry out a transvaginal scan to measure the length of the cervix.

If any abnormalities are detected the significance of the findings will be discussed and the couple will be given the opportunity to have further counselling with Professor Nicolaides.

Aims of the 11-13 weeks scan

• To date the pregnancy accurately. This is particularly relevant for women who cannot recall the date of their last period, have an irregular menstrual cycle, or who have conceived whilst breastfeeding or soon after stopping the pill. We measure the size of the fetus and from this we calculate the expected date of delivery.
• To assess the risks of Down's syndrome and other chromosomal abnormalities.
  Each woman will be given an estimate of her individual risk for this pregnancy. This is calculated by taking into account the age of the mother, measurement of two hormones in the mothers blood and the scan findings of nuchal translucency thickness, nasal bone, blood flow through the fetal heart and ductus venosus and fetal abnormalitites. Parents will receive full counselling concerning the significance of these risks and the various options for further testing.
• To diagnose multiple pregnancy. Approximately 2% of natural conceptions and 10% of assisted conceptions result in multiple pregnancy. Ultrasound scanning can determine if both babies are developing normally and if the babies share the same placenta which can lead to problems in the pregnancy. In such cases it would be advisable to monitor the pregnancy more closely.
• To diagnose certain major fetal abnormalities. Major abnormalities may be visible at this gestation but a 20 week anomaly scan is essential.
• To diagnose early pregnancy failure. Unfortunately, in 2% of women who attend for a nuchal scan it is found that the fetus has died, often several weeks before and without any warning. Couples will receive full counselling as to the possible causes of this problem and the options for subsequent measures that may be necessary.

Personalised risk for Down's syndrome

The vast majority of babies are normal. However all women, whatever their age, have a small risk of delivering a baby with a physical and/or mental handicap.

In some cases the handicap is due to chromosomal abnormality such as Down's syndrome.

The only way to know for sure whether or not the fetus has a chromosomal abnormality is by having an invasive test such as chorion villus sampling (CVS) or amniocentesis (amnio). However, these tests carry a risk of miscarriage of about 1%.

It is up to you and your partner to decide whether or not the risk of the fetus having a chromosomal abnormality is high enough to warrant having an invasive test. As a guideline, an invasive test is usually offered if the risk of Down's Syndrome is 1 in 300 or above.

The most accurate way of estimating the risk of the fetus having Down's Syndrome is carried out at 11-13 weeks and depends on the:

• Age of the mother
• Amount of fluid behind the neck of the fetus (nuchal translucency)
• Presence or absence of the fetal nasal bone
• Fetal heart rate
• Blood flow through the tricuspid valve of the fetal heart
• Blood flow through the ductus venosus in the fetal liver
• Presence or absence of any physical abnormalities
• Level of two hormones (free ß-hCG and PAPP-A) in the mother's blood

After the scan, on the basis of all the above factors, the estimated risk for Down's Syndrome will be discussed with you. Only you can then decide if you wish to have an invasive diagnostic test.

Irrespective of whether or not you decide to have an invasive test, it is recommended that you have a scan at 20 weeks to check for physical abnormalities.

This internet based course covers all the important aspects of the 11-13 weeks scan. These include first-trimester screening for chromosomal abnormalities, the diagnosis of major fetal defects and screening for preeclampsia. The course is useful for patients wishing to be better informed about this scan.

• Lasts for about one hour
• Available in 13 languages
• Free of charge
• To start the course please click here

Video lecture

This video lecture by Professor Kypros Nicolaides on first-trimester screening for chromosomal abnormalities lasts for 45 minutes and is available in English, French and Spanish. Please select your preferred language:

• English
• French
• Spanish

Nuchal translucency and nasal bone

Blood flow through the ductus venosus

Blood flow across the tricuspid valve

The aims of this scan are to determine the number of fetuses present and whether the pregnancy is progressing normally inside the uterus.

This scan is useful for women who are experiencing pain or bleeding in the pregnancy and those who have had previous miscarriages or ectopic pregnancies.

The figure on the top right shows a normal pregnancy at 7 weeks of gestation. The figure on the bottom right shows the empty san of an anembryonic pregnancy at 7 weeks.