GROUP B STREPTOCOCCAL – GBS
At around the 36th week of your pregnancy, you will have a vaginal swab taken, actually you do this yourself and take it back to the pathology service. The swab is to see if you are positive or negative to Group B Streptococcal Infection.
Group B Streptococcal or GBS as it is commonly called, is a bacteria that can cause a wid range of illnesses in susceptible people including newborn babies. Out of every 1,000 babies about 1-4 will contract GBS from their mothers during birth, although the rate is decreasing in Australia. This reduction is due to preventative screening.
In most cases, the pregnant woman will show no symptoms and will not even be aware that she is carrying the bacteria. Of the babies infected, 10-20% will become ill. Some of the complications of GBS infection in newborns include septicaemia, a bacterial infection of the bloodstream, pneumonia and meningitis ( an infection of the meninges which is the lining of the brain).
Some people are carriers of GBS without showing any symptoms of the infection. Common sites of where GBS may colonise include the vagina, bladder, the rectum and the throat. Infection is usually very short term. Around 12 -15% of pregnant women in Australia carry GBS in their vagina.
For GBS positive women in labour, intravenous antibiotics of at least two doses will be required. If less than two doses is given, the baby may require one or two blood tests, and will have a full set of observations (temperature, respiratory rate and heart rate) taken before each feed. This will of course depend upon the hospital’s protocol.
Research indicates that screening taken in late pregnancy is more reliable. Some hospitals will screen the entire pregnant population and others will only screen at risk women.
MATERNAL SERUM SCREENING TEST
The Maternal Serum Screening Test is a blood test for pregnant women to find if they may be at an increased risk of having a baby with Down Syndrome or neural tube defects. The test by itself cannot diagnose these conditions, but will identify women whou should be offered further testing.
HOW ACCURATE IS THE BLOOD TEST?
This test will help to identify pregnancies with anencephaly (abscence of a brain), four out of five neural tube defects and two out of three cases of Down Syndrome. A low risk result does not guarentee that a baby is free of other possible birth defects.
WHEN IS THE TEST DONE?
A blood test is taken between 14 and 20 weeks of pregnancy. If the blood is collected during the 14th week, no neural tube defect risk will be given. Results are usually available within one week. The results will either state low risk or increased risk.
There are two different types of maternal serum screening tests available. You can only have one or the other, not both. They are either first trimester screening or second trimester screening.
First Trimester Screening
This is a blood test done between 9 – 13 weeks of pregnancy (most reliable during the 10th week), when combined with a nuchal translucency ultrasound scan done between 11 -13 weeks of pregnancy. This test will indicate the risk of having a baby with Down syndrome and another chromosome condition called Trisomy 18. As this is a combined test, a risk cannot be calculated using the blood sample alone. If this test indicates an increased risk, the woman will be offered a diagnostic test, either CVS or amniocentesis (see further down the page).
Second Trimester Screening
Maternal serum screening, also called the quadruple test, is a blood test done between 14 – 20 weeks of pregnancy (best results are during the 15th week). This test will indicate the risk of having a baby with Down syndrome, Trisomy 18 or neural tube defects (such as spina bifida or anencephaly).
If this test indicates an increased risk for Down syndrome or Trisomy 18, the woman will be offered amniocentesis. If this test indicates an increased risk for spina bifida or anencephaly, the woman will be offered an ultrasound examination to look for neural tube defects.
Ultrasound scans involve the use of sound waves to create a picture of the baby, which is viewed on a television screen. Current knowledge suggests that there is no harmful effect on the mother or the developing baby. Ultrasound does not invlve x-ray. Ultrasound scanning can take place at any time during pregnancy.
For testing purposes, there are two ideal times for doing an ultrasound scan.
FIRST TRIMESTER ULTRASOUND
This is also called nuchal translucency ultrasound and is done between the 11th – 13th week of pregnancy. This scan measures the skin thickness at the back of the baby’s neck (nuchal translucency). When this measurement is increased, it can indicate an increased risk of having a baby with Down Syndrome or another problem. When an ultrasound is performed at an accredited centre, the result can be combined with the first trimester blood test. If this test indicates an increased risk, the woman will be offered diagnostic testing, either a chorionic villus sampling (CVS) OR amniocentesis (see further down the page for an explanation for both of these tests).
SECOND TRIMESTER ULTRASOUND
Second trimester ultrasound is sometimes called the fetal anomaly scan and is performed between the 18th – 20th weeks or pregnancy. This scan is used to identify structural problems such as limb or heart defects in the developing baby. It does not detect all abnormalities. If problems are detected, the woman will be offered further testing.
DIAGNOSTIC INVASIVE TESTS
Diagnostic tests are for the daiagnosis of specific conditions. They are called invasive because they carry a risk of miscarriage from the procedure. This risk is in addition to the natural risk of miscarriage at the time of testing. Diagnostic tests are offered when:
* There is a family history of a particular condition
* Screening tests have indicated an increased risk of a particular condition
* The fetal anomaly scan has indicated an increased risk of a particular condition
* A woman is 37 years old or more and does not choose to have screening
The most common two tests would be ultrasound and amniocentesis.
Source: Victorian Clinical Genetics Services.
ROUTINE ANTE NATAL BLOODS