Common Tests During Pregnancy
You will find throughout this section some information on tests routinely referred for in pregnancy. Remember however there is no such thing as a ‘routine’ or ‘standard’ pregnancy. Depending on your personal medical history, and how your pregnancy is progressing, you may be referred for other tests, procedures and ultrasounds. These will be discussed with you as required.
Early pregnancy blood and urine tests
Blood group and antibodies screen
It is important to know your blood group during pregnancy, as there can be an incompatibility between yours and baby’s blood. Everyone has this checked, even if it has been tested previously, as it is an important thing to be sure of. Please see the anti-D paragraph below for more information.
Full Blood Count
This looks at many components of your blood, and in pregnancy the levels of Haemoglobin (related to iron and being anaemic) and Platelets (related to blood clotting, which controls bleeding) are most important.
This test checks your iron level, which is called your Ferritin. Low Ferritin levels can cause anaemia, and in rare cases some people have too much Ferritin.
There are a group of infections that are known to cause problems for unborn babies. Most of these infections are uncommon in this day and age, however most of these are treatable. We test every expecting mother for these potential infections; Hepatitis B & C, HIV, Syphilis, Rubella (German Measles), Varicella (Chickenpox), Chlamydia and Gonorrhoea.
Pregnancy can (temporarily) cause your thyroid function to be abnormal. In most cases this is easily treated, and treatment is beneficial for mother and baby. Some women also already have a thyroid disorder, and this needs to be monitored and managed in pregnancy.
It is very common for people to have vitamin D deficiency, as Australians have become very good at slip, slop and slapping! Unborn babies need vitamin D to help develop strong healthy bones.
Midsteam Urine (MSU)
Urine infections are very common in pregnancy, and everyone has this test at their first appointment. A MSU also checks for the presence of Bacteriuria, which has been shown to cause low birth weight and preterm labour.
Screening for generic abnormalities
At your first appointment you will be offered tests to screen for genetic abnormalities of your unborn child. These are optional tests and Dr O’Neill will help you decide which test is the most appropriate for you.
First trimester screening (FTS)
This test uses a combination of blood test and ultrasound measurement to calculates your risk of a baby with Trisomy 21 (Down syndrome), Trisomy 18 (Edwards syndrome) and Trisomy 13 (Patau syndrome). This test has a detection rate of 90% for Down syndrome, and has a false positive rate of 5%. It involves a blood test performed at 10 weeks gestation, and an ultrasound performed at 12 weeks gestation. These two results are combined with your maternal age, and any relevant history, to give you an estimated risk of your baby being affected.
It is important to remember that a screening test is not diagnostic (a definite diagnosis). If this result comes back high risk you will be offered further testing, such as Non Invasive Prenatal Testing or amniocentesis. Dr O’Neill recommends the ultrasound for this screening test is performed by a specialised obstetric ultrasound practice, such as;
Non Invasive Prenatal Testing (NIPT)
Non Invasive Prenatal Testing (NIPT) is a newer option for prenatal screening. It is a blood test that analyses fetal DNA extracted from a maternal blood sample. This screening test detects the risk of your baby having Trisomy 21 (Down syndrome), 18 (Edwards syndrome) and 13 (Patau syndrome). NIPT has a detection rate of >99%, false positive and false negative rates of <1%.
NIPT usually takes 5-8 business days and currently in Perth costs approximately $425, with no Medicare rebate applicable. It is an alternative to FTS although should still be done in conjunction with a 13 week scan. Dr O’Neill will ensure you have plenty of time to discuss the right test for your circumstances. It is important to remember that a screening test is not diagnostic (a definite diagnosis). If this result come back high risk you will be offered further testing, such as an amniocentesis, and genetic counselling as required. For more information regarding NIPT please click on the following link: Harmony Prenatal Test.
A carrier is a person who has a genetic change, or mutation, in their DNA, but in most cases does not have any associated health problems. Carriers are, however, able to pass that mutation on to their children, who may then develop a genetic disorder.
Currently carrier screening tests for Cystic Fibrosis (CF), Spinal Muscular Atrophy (SMA) and Fragile X syndrome (FXS). These are the three most commonly inherited conditions with implications for childhood. The blood test is approximately $400.
CF and SMA are recessive disorders, which means both parents must pass on a mutation for their children to be affected. A couple who are both carriers for the same disorder have a 25% risk of having a child that will be affected by that disorder. The female partner is tested first and, if she is found to be a carrier, the male partner will then be tested to see if they are a carrier of the same disorder.
FXS is an X-linked disorder, which means that the mutation is found on the X chromosome (female). Female carriers of FXS have a 50% risk of passing on the mutation to their children, who in turn may develop FXS.
If you come back a carrier for CF, SMA, or FXS you will be referred to a Genetic Counsellor to discuss the result further.
ULTRASOUND IN PREGNANCY
Early Fetal Anatomy
This is the first check of a baby’s anatomy and is important in the early detection of potential abnormalities. The scan is either performed as a part of First Trimester Screening, or in parallel to NIPT. If you have decided not to have either of these blood tests, the scan is still recommended as a screen for anatomical abnormalities.
Anatomy Ultrasound (18-20 weeks gestation)
The Anatomy Ultrasound, or sometimes called the Morphology Ultrasound, is performed between 18-20 weeks gestation. Its major role is to detect structural abnormalities in the fetus, such as heart, limbs, abdomen, bones, brain, spine and kidney. At that time the position of your placenta, amniotic fluid and baby’s growth will also be assessed. This is also a good time to find out the sex of your baby if you wish.
Dr O’Neill recommends this ultrasound is performed by a specialised obstetric ultrasound practice, such as:
In some circumstances, additional testing for your pregnancy may be recommended. These are arranged with a specialist Obstetric ultrasound service.
Chorionic Villus Sampling (CVS)
Chorionic Villus Sampling (CVS) is a diagnostic test performed at 11 to 14 weeks gestation. It is performed by taking a sample of chorionic villus cells from the placenta with an ultrasound guided needle. The risk of miscarriage is 1-2%. That means there are between one and two chances of miscarriage for every 100 sampling tests performed.
This procedure is usually recommended if you have a high risk for chromosomal abnormalities on NIPT, or have a family history of a genetic condition. It requires referral to an obstetric ultrasound specialist to be performed.
Amniocentesis (Amnio) is a diagnostic test performed at 15-18 weeks gestation. It is performed by taking a small sample of amniotic fluid from around the baby with an ultrasound guided needle. The risk of fetal loss is 0.5-1% as a result of amniocentesis under ultrasound guidance. That means there are between one and two chances of miscarriage for every 200 Amnio performed.
This procedure is usually recommended if you have a high risk NIPT, or have a family history of a genetic condition. It requires a referral to an obstetric ultrasound specialists to be performed.
TESTS IN LATER PREGNANCY
Gestational Diabetes (26-28 weeks gestation)
Current Australian guidelines recommend all pregnant women have a Glucose Tolerance Test (GTT) at 26-28 weeks gestation. At that time you will have a recheck of your full blood count, antibodies screening, iron studies and thyroid function. Your vitamin D will also be rechecked if this was low at the beginning of your pregnancy. You may be referred for a Diabetes test earlier if you are at risk of early onset Gestational Diabetes.
The GTT is a blood test that measures how quickly your body responds to a glucose load. Women whose bodies are slower to respond to the glucose are considered to have Gestational Diabetes.
If you are found to have Gestational Diabetes you will be referred to a Gestational Diabetes Educator for advice.
If you would like more information regarding Gestational Diabetes please click the following link: Gestational Diabetes
Group B Streptococcus Screening
If you are planning to have a vaginal birth Dr O’Neill will advise you to have a vaginal swab at 35-37 weeks gestation. This is to check if you have the bacteria Group B Streptococcus. This is a normal bacteria that many women carry without being aware of it, however, in rare cases it can be harmful to the baby during vaginal delivery.
If you are known to have Group B Streptococcus you will be prescribed antibiotic treatment during labour.
If you would like some more information regarding Group B Streptococcus click on the following link: Group B Streptococcus.