First Trimester Tests

Most women book with us for antenatal care during the first trimester. At your booking visit we will arrange a number of blood and other tests. We will also discuss second trimester tests that are available to screen for Down syndrome. We have an ultrasound scanner in our clinic and can confirm that your due date is correct, check for baby's heart beat and confirm whether you are pregnant with one baby or with twins.

Your booking blood tests include:

A full blood count - This is to check for anaemia

Blood group and antibody screen - This is to check your blood group (A, B, O or AB) and rhesus group (positive or negative). Blood group antibodies that might interfere with cross matching blood for a transfusion or cause anaemia in a developing baby are also checked for.

Rubella serology - This is to check that you are immune to rubella (german measles). Most women have been vaccinated against rubella in their early teens but a few women will have little or no immunity.

Hepatitis B - This checks for infection or immunity to hepatitis B. Hepatitis B carriers can pass hepatitis onto their children and the babies of carriers are usually immunised shortly after birth.

VDRL - This screens for syphilis. This is now a rare disease but if detected treatment in pregnancy can prevent baby being infected.

HIV screening - HIV (the virus that causes AIDS) is still rare in pregnant women but carriers can infect their unborn child. Treatments are very effective in reducing this risk in women found to be carriers for HIV.

MSU (mid-stream urine) - A urine sample can check for unexpected urine infection or the presence of bacteria in your urine that increases your risk of kidney infections later in pregnancy.

Second Trimester Tests

Vaginal swabs - Infections such as Chlamydia, which often cause few or no symptoms, can be checked for in pregnancy though we usually wait until between 12 and 18 weeks to screen for this.

Anatomy scan - At 18 to 20 weeks of pregnancy most women have an anatomy scan. This is a detailed scan to check baby's brain, heart, spine and other important organs. The great majority of babies will be normal and couples find an anatomy scan very reassuring. Occasionally, an abnormality is detected and this can have important implications for your baby's care. For example, it may be necessary to arrange for baby to have a surgical procedure soon after birth. Some couples are very anxious that a severe abnormality will be found and a termination suggested. This is a very rare event and in most cases finding an abnormality can help paediatricians plan any treatment baby might need after it's born. It is also important to realize that not all problems and abnormalities will be detected.

It is often possible to tell if baby is a boy or girl but this is not the primary purpose of the scan. At best, the sonographer can only give you a strong idea about baby's gender. You may be offered a 4D ultrasound which produces very detailed pictures of baby but there is no particular medical reason to have a 4D scan.

Polycose test - this is done at about 26 to 28 weeks of pregnancy to check if you are at an increased risk of developing gestational diabetes. You will be given a sugary drink and an hour later some blood is taken. If your blood sugar is unexpectedly high you may need a further more detailed test called a Glucose Tolerance Test (GTT). For this test you will need to miss breakfast and then have blood taken before having a glucose drink and have more blood taken at one and then two hours later.

Gestational diabetes is associated with high blood sugars in pregnancy. Exposure to high sugar levels can result in baby becoming excessively large. Women who develop gestational diabetes are also at greater risk of developing diabetes in later life.

Blood group antibody screen, full blood count and ferritin levels - These are also checked at the same time as your polycose test to look for signs of anaemia and the development of antibodies to baby's blood group.

Third Trimester Tests

Ultrasound scans - If there is a concern that your baby is too small or large we will organise an ultrasound scan to check that your baby is growing appropriately. Most women will not need any ultrasound scans after their 18 week anatomy scan. A few women may need several scans to monitor all is well with baby. If you go past your due date then ultrasounds scans will be arranged to check that there is still plenty of fluid around baby.

Cartiotocographs (CTG) - Sometimes in late pregnancy it is important to check all is well with a CTG machine that monitors baby's heart beat and movement. This is particularly helpful if you are still pregnant after your due date or there are worries about baby's movements.

Blood tests - Don't worry - most women don't need any blood tests after their polycose test. Women who are rhesus negative or have blood group antibodies will usually have further tests at 34 weeks. Women with blood pressure problems or medical problems may need regular blood tests especially towards the end of their pregnancy.

Screening for Down Syndrome

Both ultrasound and blood based tests are available to screen for Down syndrome. Ideally, these tests are done before 14 weeks of pregnancy and the results of these two tests are combined to produce a single result which is given as "risk" (for example 1 in 500 or 1 in 2000). For women booking for pregnancy care after 14 weeks it is also possible to have a blood test alone.

Many couples find their screening options confusing. We are here to help you understand the options that are available to you.

What is Down Syndrome? - A normal child has 23 pairs of chromosomes. A child with Down syndrome has an extra twenty first chromosome (the condition is sometimes called Trisomy 21). This is the result of an abnormality arising at the moment of conception. Why it occurs is unknown. It becomes commoner with increasing maternal age. For example at 30 years of age a woman has a one in 350 chance of carrying a baby with Down syndrome when she has screening tests at 11 to 14 weeks. By 40 years of age this rises to one in 100. Down syndrome is equally common in all ethnic groups. Children with Down syndrome have a varying degree of intellectual disability. Some have other serious medical problems but many children with Down syndrome will lead fulfilling lives.
For more information look at the websites listed on our useful websites page.

FIRST TRIMESTER COMBINED SCREENING - Pre-natal screening for Down syndrome consists of a blood test taken at between 9 and 14 weeks of pregnancy (ideally between 10 and 12 weeks) and an ultrasound scan (called a nuchal translucency scan) performed at 11 to 14 weeks of pregnancy. A separate blood test at 14 to 20 weeks of pregnancy can also be offered to women who did not have any screening tests earlier in their pregnancy.

These screening tests start with a risk based on your age. They then calculate your personal risk based on the levels of two substances in your blood and an ultrasound measurement taken from the back of baby's neck. The two substances in your blood (called pregnancy-associated plasma protein (PAPP-A) and beta-human chorionic gonadotrophin (Beta-hCG)) tend to occur at different levels in pregnancies affected by Down syndrome. The thickness of the skin at the back of baby's neck (the nuchal translucency measurement) tends to be increased in babies that have Down syndrome. By putting all these measurements together your personal risk of carrying a baby affected by Down syndrome is calculated. Together these tests are referred to as first trimester combined screening.

Both these tests are completely safe and will provide you with a risk measurement. They are screening tests - they will provide an accurate assessment of your risk but won't give you a definite yes or no answer. This risk is given to you as a number - for example 1 in 100 or 1 in 500.

Used together as a screening test about 80 to 90 per cent of babies affected by Down syndrome will be picked up. It is impossible for all babies affected by Down syndrome to be picked up because even for women at very low risk, an occasional baby will have Down syndrome (for example, for a risk of one in one thousand, every thousandth baby will have Down syndrome).

One purpose of the screening tests is to help many women avoid amniocentesis. The risk of having a baby with Down syndrome increases with age but most older women who might have considered an amniocentesis because of their age will still have a reassuring result from these tests.

Overall about 3% to 5% of women will opt to have an amniocentesis or CVS after the first trimester combined screening test. This proportion will be slightly higher in older women because their initial pre-test risk based on their age alone will be higher.

SECOND TRIMESTER SERUM SCREENING - Women booking for antenatal care after 14 weeks of pregnancy (too late for a nuchal translucency scan) can still have a screening blood test (this is called second trimester serum screening). This can be done at up to 20 weeks of pregnancy (ideally between 14 and 18 weeks). This test also takes your risk based on your age alone and calculates a personal risk based on the levels of the different substances checked in your blood.

This later test is not quite as reliable as the combined first trimester test. There is no need to have this later test done if you have already had the earlier combined test.

AMNIOCENTESIS - This test is usually done at between 15 and 17 weeks of pregnancy. A needle is passed through your abdominal wall into the fluid around baby - an ultrasound scan is used to guide the needle and make it a safe procedure for baby. Local anaesthetic can be used to make it a more comfortable procedure for you. A small amount of fluid is drawn off. Within this fluid are some of baby's skins cells that can be cultured in the laboratory to check the chromosomes.

It can take 10 to 14 days to get a result from this test. A more rapid test (called FISH) is available that can check for Down syndrome within 24 to 48 hours is also available but at an additional cost - the doctor performing your amniocentesis can discuss this option with you.

Amniocentesis is a quick procedure taking about 10 to 15 minutes to set up and only a few minutes to do. You are welcome to bring your partner or a support person along and should plan to have a quiet 24 hours after the test. It does have a small risk of miscarriage. For every 150 women having an amniocentesis one woman will miscarry as a result of the procedure.

CHORIONIC VILLUS SAMPLING - This is similar to amniocentesis but it can be done a couple of weeks earlier in pregnancy. A small piece of tissue is obtained from baby's placenta using a similar needle to the one used for an amniocentesis. Technically it is more difficult to do with possibly a slightly higher rate of miscarriage. It tends to be done in women with a particularly high risk of having a baby with a chromosomal abnormality.

USEFUL SOURCES OF INFORMATION - For many couples, decision making around Down syndrome screening is straightforward and their test results are reassuring. All of us at AOC are aware that for some couples making these decisions is terribly difficult - we are very happy to talk to you by phone between appointments or arrange extra visits to clinic if you need more help in deciding what tests to have.

We can provide you with additional written information to help guide your decision making. You can download our information leaflet on screening tests in early pregnancy here. Useful websites are also listed on our websites and information page.