Down's syndrome is a condition caused by the presence of an extra chromosome in a baby's cells. It occurs by chance at conception and is irreversible, it is not caused by anything either parent has done. There is no such thing as a typical person with Down's syndrome, they vary a lot in appearance and ability, but are at an increased risk of health problems such as learning difficulties and heart and bowel problems. It is not possible to tell how much a baby will be affected when they grow up. All pregnant women should be offered screening for Down's syndrome.
These tests can show if there is an 'increased chance' or 'higher risk' of your baby having Down's syndrome. Agreeing to a screening test does not mean you have decided what to do if a problem is found. Some couples simply prefer to know in order to be prepared, whilst others choose to end their pregnancy. More @ How is my baby going to be screened for Down's syndrome and fetal anomalies?
The tests: the National Screening Committee (NSC ) of UK recommends screening is available early in pregnancy. The test offered does depend on how early we see you in your pregnancy. A combination of blood tests and an ultrasound scan are available. Your doctor will give you more information about the tests available locally.
- Blood Test: a sample is taken from the mother and sent to the laboratory to measure the levels of chemicals or substances naturally found in your blood and those passed from the baby.
- Nuchal Translucency (NT ) scan: this is a special ultrasound scan done between 11 and 13 weeks. The amount of fluid lying under the skin at the back of the baby's neck is measured and the result added to the measurement from the blood test.
- The combined test: a combination of the result of the NT scan and a blood test, offered early in pregnancy - Between 11 to13+6 weeks is offered in Hong Kong.
- The triple or quad test: a combination of a number of chemicals found in the blood, available after 15 weeks and before 20 weeks.
The result: Your risk or chance of having a baby with Down's syndrome is calculated as above or below NSC recommended cut-off limit. Your result should be available within one week and your doctor will tell you how you will get your results.
High result: it is most likely that your baby does not have Down's syndrome. You will be offered an additional test to make an accurate diagnosis, such as CVS or Amniocentesis. More information about these tests are in "Diagnostic Tests for Chromosomal Abnormalities" section.
Low result: it is important to be aware that none of the tests are 100% accurate, they detect between 70-90% of all cases.
You will be offered one or two routine ultrasound scans in the first half of pregnancy (i.e. usually by 20 weeks ). As with blood tests, it is up to you to decide whether you want any scans to be performed in your pregnancy. The scientific evidence is that ultrasound scanning during pregnancy is safe for mother and baby.
It is important to be aware of what the scans are intended for.
Most scans fall into one of three categories:
- Early scans to check the number of babies and to date the pregnancy
- Anomaly scans, recommended to be done at about 20 weeks
- Scans later in pregnancy, not done routinely but when there are doubts
about the baby's growth and wellbeing, or about the position of the placenta
Reasons for Scans
Dating pregnancies. It is important to know the age of the baby in the womb so that we know how mature the fetus is. Scan dates are more accurate than menstrual dates if done before 22 wks. This is because they look at the actual age of the fetus, whereas menstrual dates are based on the first day of the last menstrual period and assume that fertilization has occurred 14 days later, which is not always the case. Please note also that most babies are NOT born on their actual due date, but during a 4 week period around it. Usually babies come when they are ready.
Early pregnancy ultrasound scan. It is standard to offer you an early scan between 10 weeks and 13 weeks and 6 days to confirm the pregnancy and the number of babies in the womb, and to calculate the date of delivery. Some units check for nuchal translucency at this time, as one method to screen for Down's syndrome.
Anomaly scan. A detailed scan is usually offered at 18-21 weeks gestation. This is a good time to check for abnormalities (anomaly ) of the head, spine, limbs, abdomen and heart of the baby. However, it is important to understand that ultrasound will not identify all problems. Detection rates will vary depending on the type of anomaly, the position the baby is lying in, previous surgery to your abdomen and maternal size. If a problem is suspected you will be referred to a specialist to discuss the options available to you. Sometimes problems are suspected in normally developing babies. List of the most common anomalies and the chance of it being identified on ultrasound is
Anencephaly 97 - 100
Spina bifida 61 - 92
Major cardiac anomalies
(Hypoplastic ventricle )14 - 61
Diaphragmatic hernia 30 - 62
Gastroschisis 86 - 100
Exomphalos 45 - 92
Major renal tract problems
(Renal agenesis ) 76 - 85
Scans to check the baby's well-being later in pregnancy. An ultrasound scan can check what size the baby has reached at a particular point in pregnancy. The main measurement for this is the abdominal circumference, which includes the size of the liver (the main nutritional store of the growing baby ) and the abdominal wall thickness (related to fat reserves ). Scans to measure fetal size are usually not done routinely, but if there is a suspicion that the baby may not be moving or growing well. An assessment of the amount of amniotic fluid (liquor ) around the baby is also important, as low liquor is linked to fetal growth restriction and can cause fetal distress. If the scan suggests that the baby may be small, Doppler flow studies can establish whether the baby is receiving sufficient blood flow with oxygen and nutrients through the placenta (afterbirth ). Scans are sometimes also done to examine and identify the position of the placenta, which may have been low in the womb at an earlier scan. A low placenta increases the risk of heavy bleeding later in pregnancy.
Sex of the Baby. Although the scan can sometimes tell whether the baby is a boy or girl, this is not always accurate. Please note, scans are NOT done to find out what the sex of the baby is, unless requested by the parents.
Diagnostic tests (Amniocentesis or CVS )are usually offered to detect whether or not a baby has a chromosomal condition such as Down's syndrome. They are not offered on a routine basis, but when the result of a screening test is reported as 'high chance', to anyone with a family history of an inherited problem, or as a result of scan findings. It is important to remember that you have a choice of whether or not to undergo this procedure. Your doctor will discuss with you the options available.
Amniocentesis: is a diagnostic test which involves removing a small amount of the fluid from around the baby using a needle. It is normally performed after 15 weeks. The risk of miscarriage from amniocentesis is approximately 1 in 100.
CVS (Chorionic Villus Sampling ): is a diagnostic test which involves removing tiny amounts of the placenta (afterbirth ), using a needle. This can be done from 10 weeks, but usually is only performed from 11 weeks. The chance of miscarriage is similar or slightly higher than with amniocentesis. Occasionally results from CVS are not clear and you will then be offered an amniocentesis.
There are two types of laboratory test which can be used to look at the baby's chromosomes - a full karyotype and a rapid test (PCR ). A full karyotype, checks all of the baby's chromosomes and takes 2 to 3 weeks. PCR checks for specific chromosomes, and results take up to 4 working days. Sometimes a test to detect Down's syndrome will find another chromosomal problem, e.g. Edward's or Turner's syndrome
All pregnant women are offered regular antenatal appointments to monitor their and their baby's health, provide support and give adequate information to help make informed choices. The frequency of these appointments will vary from woman to woman, and may need to be adjusted according to circumstances as the pregnancy progresses. Part of the assessment at each antenatal contact is to identify any additional need you may have, e.g medical, personal or family problems. It is also important to ensure that after each of your antenatal contacts you know when your next appointment is, where it will take place and with whom.
Up to 20 weeks:
The aim of early visits is to record details about you and your pregnancy which are relevant for your care, provide information about your choices for antenatal screening, discuss healthy lifestyles and asses which additional services you might need to be offered.
From 20 weeks:
Visits in the second half of pregnancy aim to monitor your health and to check that your baby is well and growing as expected. Also they provide continuing opportunities to discuss expectations and options for childbirth, and to prepare for motherhood.
Most pregnancy symptoms are normal. However it is important to be aware that certain symptoms might suggest possibility of serious pregnancy complications. Contact your doctor or midwife or maternity unit IMMEDIATELY if any of these occur:
Severe headache ; Blurred vision ; Persistent itching ; Changed or reduced fetal movements.
To deal with special issues during pregnancy, a management plan will outline specific treatment and care agreed between you and your care providers. The aim is to ensure that everyone involved in your care is aware of your individual circumstances. This plan will be updated and amended as the pregnancy progresses, to reflect your changing needs.
Your midwives and doctors would like to make your birth experience special, while also making sure that it is safe. A birth plan is a record of what you would like to happen. It allows the professional caring for you to know your wishes and understand your individual needs. It is good to make plans but please remember that every birth is different as the course of labor is unpredictable. Lack of flexibility can lead to disappointment when things do not happen exactly as planned- the most important thing is to keep an open mind.