Prenatal TestsPrenatal testing holds a significant place nowadays for every pregnant woman, as they are provide both you and your doctor with a wealth of knowledge about that health of your developing child.
Why are They so Important?
All prenatal tests are very specific in nature and are used to draw particular conclusions about the child and mother. Some are routine prenatal tests given to all expectant mothers while others are carried out to discern whether a mother is affected by a certain ailment. Numerous tests are also available that can detect infections or abnormalities, which can allow for early treatment if necessary
Mother’s that are older than 35, have had a premature delivery, previously delivered a child with a birth defect, suffer from high blood pressure or a chronic disease, or have a family history of genetic abnormalities may require additional tests to ensure both their health and the health of their baby.
Types of Prenatal Tests
One of the very first tests you will receive from your doctor is a pregnancy test to confirm your pregnancy. The pregnancy tests performed at the doctor are blood tests that look for the presence of a protein called human chorionic gonadotropin (hCG), which is produced only during pregnancy. In addition to the pregnancy test, you may also receive a pelvic exam on your first visit.
However, there are a number of other tests routinely given during pregnancy. Some you will receive at every visit, others only at certain times.
Non Invasive Prenatal Testing (NIPT)
Prenatal diagnostic tests can be divided in two: invasive fetal DNA sampling methods such as chorionic villus sampling or percutaneous umbilical cord sampling and non invasive prenatal tests. Non invasive prenatal tests differ mainly in the fact that they are 100% risk free and pose no risk of miscarriage. Non invasive prenatal testing is done via a medical blood draw from the arm – at most, the expectant mother from whom the blood has been drawn may suffer from minor soreness at the point where the needles has pierced the vein. Companies offering this test send out a special kit which contains vacutainer blood collection tubes – the tubes include a special anticoagulant which preserves the baby’s DNA in the blood sample ensure better chances of successful fetal DNA extraction.
Non invasive prenatal paternity testing: Non invasive prenatal testing can be used to confirm the paternity of an unborn baby. The results are 99.9% accurate and a number of laboratories are offering this test, including International Biosciences. The test can be carried out at around 10 weeks. Laboratories require a minimum volume of fetal DNA in the blood sample to be able to complete the extraction process. In some cases, the blood sample provided might not contain enough fetal DNA which can lead to the laboratory not being able to produce a result. This may happen if the blood is collected too early in the pregnancy as the volume of fetal DNA increases as pregnancy progresses, meaning that in the earlier weeks of pregnancy, the volume of fetal DNA is typically very low.
Fetal sex determination: The NIPT test has multiple uses –another of these is fetal sex determination. In this case, due to the fact the test can be carried out at just 10 weeks, couples do not need to wait till their 18th prenatal testing for fetal sex determination are also much higher than ultrasonography. Generally, using non invasive or NIPT testing for fetal sex determination is used if there is a suspected risk of sex linked diseases. By knowing the sex of the unborn baby, couples can decide whether to keep the baby or terminate the pregnancy or opt for further tests if the sex of their baby is linked to a particular disease such as Duchenne Muscular Dystrophy – a disease which is found predominately in males.
Down’s syndrome: For Down syndrome detection, an NIPT test reaches near 100% accuracy but a prenatal care specialist or gynaecologist will still suggest invasive prenatal testing should the results of the NIPT test show a high chance of the fetus having Down syndrome. An invasive test will be especially recommended if the couple is considering a termination of pregnancy. Significantly, the detection rate will differ depending on how the test is carried out and the technology used; some laboratories actually separate the cell-free fetal DNA from the maternal DNA in the blood sample whilst other laboratories lack such sophisticated capabilities and simply work by counting the total number of chromosomes. The NIPT Down syndrome test has been endorsed by American College of Obstetricians and Gynecologists (ACOG1) and the Society of Obstetricians and Gynaecologists of Canada (SOGC). However, all professionals suggest consulting a genetic counselor or a specialist about the results of the test.
This is done for the following reasons:
- To know your blood type
- To determine your Rh factor. If you are not compatible with your baby, you may be given some injections to avoid the antibodies formed in the body that might harm the baby.
- Check that you are not anaemic
- Check for HIV, hepatitis B and syphilis
- Immunity to chickenpox and German measles
These tests are mainly carried out to determine the amount of sugar and protein in your system as well as look for the presence of any infection.
The presence of glucose in the urine may be a sign of gestational diabetes that can develop after the 20th week of pregnancy. Those who develop gestational diabetes can monitor glucose using devices from Dexcom. This kind of diabetes may cause some complications in the child such as giving birth a baby that is large for gestational age, respiratory problems or your baby may develop hypoglycaemia, a conditions where the baby’s blood glucose falls very low after delivery. Gestational diabetes can eb treated through dietary changes and insulin treatment when necessary.
The presence of protein in the urine along with high blood pressure is a sign that a mother may have pre-eclampsia. This is a pregnancy related condition, which, if left untreated, may result in poor growth of the baby as well as chances of premature delivery. In rare cases, maternal death may occur.
The mother’s blood pressure is measured at every prenatal visit to ensure that she does not have high blood pressure or pregnancy induced hypertension, which may lead to premature delivery, retarded growth or low blood flow to the baby.
Nowadays doctors continuously monitor the foetal heartbeat with the help of a Doppler machine. This gives a fair idea of the baby’s well being and growth in the womb.
This test is done to again check for gestational diabetes. Women at high risk of developing this type of diabetes will be tested at 12 weeks; other women are routinely tested between 24 and 28 weeks. In this test you may be asked to drink a sugary liquid and a blood sample will be drawn. If the glucose level is high, you may undergo a glucose tolerance test, which will again require you to drink a sweet liquid on an empty stomach. Blood samples will be drawn every hour to 3 hours, to confirm gestational diabetes.
These are done at various stages of pregnancy when the doctor takes cell samples from the cervix, vagina or rectum to find out the presence of any infection or disease. A Pap smear is done usually during the first trimester to see if you may have cervical cancer. At a later stage, approximately 35 weeks of pregnancy, a swab is taken from the vagina or rectum to check for the presence of streptococcus bacteria, which may cause problems to the baby.
The prenatal ultrasound, done at various stages of pregnancy, allows you and your doctor to see your developing baby and evaluate its growth. The different information inferred from a pregnancy ultrasound are:
- The due date
- Growth of the baby at a normal rate
- Record foetal heartbeat and movement
- Verify a multiple pregnancy
- Identify abnormalities if any
- See that the amniotic fluid surrounding the child is adequate
- Position of the placenta
- Check that pregnancy is not ectopic
- As an aid with other tests, like CVS
- Structural defects like spina bifida or heart defects
- Other birth defects
The number of ultrasounds you might have depends on your health care provider and if you have a high-risk pregnancy.
Testing for Diseases, Disorders, and Defects
Aside from the routine tests, there are a number of other tests that can be done upon request.
Combined First Trimester Screening
This is a rather uncommon test at the moment, though it is increasingly getting recognition as a means of detecting baby’s risk for Down’s syndrome or other genetic disorders. During the first trimester, a test called nuchal translucency screening might be performed, which is an ultrasound check up of the clear space at the back of the baby’s neck. The presence of any fluid at this place may be a sign of abnormalities.
The combined screening adds one or two blood tests with the nuchal translucency measurements to make the test results more accurate. This is performed between 11 and 14 weeks of pregnancy. While the test can indicate that your child may have an increase risk of Down's Syndrome, it does not guarantee that your child will have Down’s Syndrome. Further testing may be necessary to fully evaluate your child’s risk.
Triple Screen Test
This test is done in the second trimester to measure three things, the alpha fetoprotien, hCG and estriol. Alpha fetoprotien is usually produced by the baby and is present in the mother’s blood in low quantities. If the level of the protein is high, it may indicate the presence of neural tube defects. On the other hand, a high level of hCG with a low level of AFP may suggest chromosomal abnormalities.
Estriol is a hormone produced by the baby’s adrenal glands and if this level is low it can suggest that the baby is not developing properly or it may indicate a birth defect.
This test is also known as the multiple marker test and is usually performed between 15 and 20 weeks when a blood sample is analysed for the various hormones and proteins. Again, a positive test does not necessarily mean that your baby will definitely have a birth defect.
A test especially beneficial for those at risk of having a baby with birth defects or where the mother is over 35 years, amniocentesis helps analyse the presence of chromosomal abnormalities, structural defects or metabolic disorders.
For this test, the doctor injects a needle through the abdomen into the uterus to get a sample of the amniotic fluid, which is then examined for possible defects. An ultrasound helps identify the best place to insert the needle without harming the baby. However, there is still a small risk of miscarriage associated with this test.
Chorionic Villus Sampling (CVS)
The mother’s placenta is made up of tiny finger like units, which are called chorionic villi. Taking a sample of these units can help detect birth defects like chromosomal abnormalities. As this test can be performed at an early stage of pregnancy (between 10 and 12 weeks), it is preferred over amniocentesis as it gives a better chance of diagnosis and treatment.
The test can either be performed by removing the sample vaginally or through the abdomen with an injection and guide from ultrasound. Again, though, there is a risk of miscarriage associated with the procedure.
This test is generally performed during high-risk pregnancies or when a pregnancy has gone beyond its due date. It is a way of measuring the baby’s response to stimuli and done by tracking its movements through an ultrasound and observing the accelerating or decelerating heart beat. This test give s the doctor an idea of whether the baby is getting enough oxygen and if her nervous system is functioning normally.
Contraction Stress Test
If a non-stress test indicates a problem, this test is performed to check the baby’s heart beat during contractions. An artificial hormone, called pitocin similar to oxytocin secreted during childbirth, is given to the mother to ensure that a baby’s heart rate will remain stable during contractions.
Percutaneous Umbilical Blood Sampling
If the child may have a risk of birth defect or genetic disorder, this test is carried out to obtain a sample of the umbilical blood and analyse this for any chromosomal anomaly. This test may also be used for transfusion of blood or required fluid in the baby’s system.