Prenatal Screening Tests
What Are Prenatal Screening Tests?
Prenatal screening tests are a set of procedures that are performed during pregnancy on expectant mothers to determine whether a baby is likely to have specific birth defects. Most of these tests are noninvasive. They’re usually performed during the first and second trimesters, although some are performed during the third.
A screening test can only provide your risk, or probability, that a particular condition exists. When the results of a screening test are positive, diagnostic tests can provide a definitive answer.
Some prenatal screening tests are routine procedures, such as glucose tolerance tests, which check for gestational diabetes. Women who have a higher risk of having a child with certain conditions are usually offered additional screening tests. For example, pregnant women who’ve lived in regions where tuberculosis is common should have a tuberculin skin test.
When Are Prenatal Screening Tests Done?
First trimester screening tests can begin as early as 10 weeks. These usually involve blood tests and an ultrasound. They test your baby’s overall development and check to see if your baby is at risk for genetic conditions, such as Down syndrome. They also check your baby for heart defects, cystic fibrosis, and other developmental problems.
Second trimester screening tests occur between 14 and 18 weeks. They can involve a blood test, which tests whether a mother is at risk for having a child with Down syndrome or neural tube defects, as well as an ultrasound.
First Trimester Screening Tests
Ultrasound
An ultrasound uses sound waves to create an image of the baby in the uterus. The test is used to determine the size and position of your baby, confirm how far along you are in your pregnancy, and find any potential abnormalities in the structure of your baby’s growing bones and organs.
A special ultrasound called a nuchal translucency ultrasound is performed between the 11th and 14th weeks of pregnancy. This ultrasound checks the accumulation of fluid at the back of your baby’s neck. When there’s more fluid than normal, this means there’s a higher risk of Down syndrome.
During the second trimester, a more detailed ultrasound, which is often called a fetal anatomy survey, is used to evaluate the baby carefully from head to toe for any birth defects. However, not all birth defects are visible by ultrasound.
Early Blood Tests
During the first trimester, two types of blood tests called a sequential integrated screening test and a serum integrated screening are conducted. They’re used to measure the levels of certain substances in your blood, namely, pregnancy-associated plasma protein-A and a hormone called human chorionic gonadotropin. Abnormal levels of either mean there’s a higher risk of a chromosome abnormality.
At your first prenatal visit, your blood may also be tested to see if you’re immunized against rubella and to screen for syphilis, hepatitis B, and HIV.
A blood test will also be used to determine your blood type and Rh factor, which determines your Rh compatibility with your growing fetus. You can be either Rh-positive or Rh-negative. Most people are Rh-positive, but if a mother is found to be Rh-negative, her body will produce antibodies that will affect any subsequent pregnancies.
When there’s an Rh incompatibility, most women will be given a shot of Rh-immune globulin at 28 weeks and again a few days after delivery. Incompatibility occurs if a woman is Rh-negative and her baby is Rh-positive. If the woman is Rh-negative and her baby’s positive, she’ll need the shot. If her baby is Rh-negative, she won’t.
Chorionic Villus Sampling
Chorionic villus sampling is an invasive screening test that involves taking a small piece of tissue from the placenta. It’s usually performed between the 10th and 12th weeks and is used to test for genetic abnormalities, like Down syndrome, and birth defects. There are two types. One type tests through the belly, which is called a transabdominal test, and one type tests through the cervix, which is called a transcervical test.
Testing has some side effects, like cramps or spotting. There’s also a small risk of miscarriage.
Second Trimester Screening Tests
Blood Tests
A quad marker screening test is a blood test conducted during the second trimester. It’s done to test your blood for indications of birth defects, such as Down syndrome. It measures four of the fetal proteins.
A quad marker screening is typically offered if you start prenatal care too late to receive either the serum integrated screening or the sequential integrated screening. It has a lower detection rate for Down syndrome and other birth defects than a sequential integrated screening test or serum integrated screening test.
Glucose Screening
A glucose screening test checks for gestational diabetes. This is usually a condition that can develop during pregnancy. It’s usually temporary. Gestational diabetes can increase your potential need for a caesarean delivery because babies of mothers with gestational diabetes are usually born larger. Your child may also have low blood sugar in the days following delivery.
The test is usually performed during the second trimester. It involves drinking a sugary solution, having your blood drawn, and then checking your blood sugar levels. If you do test positive for gestational diabetes, you have a higher risk of developing diabetes within the following 10 years, and you should get the test again after the pregnancy.
Amniocentesis
During amniocentesis, amniotic fluid is removed from the uterus for testing. Amniotic fluid surrounds the baby during pregnancy. It contains fetal cells with the same genetic makeup as the baby, as well as various chemicals produced by the baby’s body. There are several types of amniocentesis.
A genetic amniocentesis tests for genetic abnormalities, such as Down syndrome and spina bifida. A genetic amniocentesis is usually performed after week 15 of the pregnancy. It may be considered if:
a prenatal screening test showed abnormal results
you had a chromosomal abnormality during a previous pregnancy
you’re 35 or older
you have a family history of a specific genetic disorder
you or your partner is a known carrier of a genetic disorder
A maturity amniocentesis is performed later, during the third trimester, to determine whether or not your baby’s lungs are ready for birth. This diagnostic test is only done if a planned early delivery through either induction of labor or a cesarean delivery is being considered for medical reasons. It’s usually done between weeks 32 and 39.
Prenatal Screening Tests
Types of Tests
First Trimester
Second Trimester
Third Trimester
Prenatal Diagnostic Tests
Takeaway
What Are Prenatal Screening Tests?
Prenatal screening tests are a set of procedures that are performed during pregnancy on expectant mothers to determine whether a baby is likely to have specific birth defects. Most of these tests are noninvasive. They’re usually performed during the first and second trimesters, although some are performed during the third.
A screening test can only provide your risk, or probability, that a particular condition exists. When the results of a screening test are positive, diagnostic tests can provide a definitive answer.
Some prenatal screening tests are routine procedures, such as glucose tolerance tests, which check for gestational diabetes. Women who have a higher risk of having a child with certain conditions are usually offered additional screening tests. For example, pregnant women who’ve lived in regions where tuberculosis is common should have a tuberculin skin test.
When Are Prenatal Screening Tests Done?
First trimester screening tests can begin as early as 10 weeks. These usually involve blood tests and an ultrasound. They test your baby’s overall development and check to see if your baby is at risk for genetic conditions, such as Down syndrome. They also check your baby for heart defects, cystic fibrosis, and other developmental problems.
Second trimester screening tests occur between 14 and 18 weeks. They can involve a blood test, which tests whether a mother is at risk for having a child with Down syndrome or neural tube defects, as well as an ultrasound.
First Trimester Screening Tests
Ultrasound
An ultrasound uses sound waves to create an image of the baby in the uterus. The test is used to determine the size and position of your baby, confirm how far along you are in your pregnancy, and find any potential abnormalities in the structure of your baby’s growing bones and organs.
A special ultrasound called a nuchal translucency ultrasound is performed between the 11th and 14th weeks of pregnancy. This ultrasound checks the accumulation of fluid at the back of your baby’s neck. When there’s more fluid than normal, this means there’s a higher risk of Down syndrome.
During the second trimester, a more detailed ultrasound, which is often called a fetal anatomy survey, is used to evaluate the baby carefully from head to toe for any birth defects. However, not all birth defects are visible by ultrasound.
Early Blood Tests
During the first trimester, two types of blood tests called a sequential integrated screening test and a serum integrated screening are conducted. They’re used to measure the levels of certain substances in your blood, namely, pregnancy-associated plasma protein-A and a hormone called human chorionic gonadotropin. Abnormal levels of either mean there’s a higher risk of a chromosome abnormality.
At your first prenatal visit, your blood may also be tested to see if you’re immunized against rubella and to screen for syphilis, hepatitis B, and HIV.
A blood test will also be used to determine your blood type and Rh factor, which determines your Rh compatibility with your growing fetus. You can be either Rh-positive or Rh-negative. Most people are Rh-positive, but if a mother is found to be Rh-negative, her body will produce antibodies that will affect any subsequent pregnancies.
When there’s an Rh incompatibility, most women will be given a shot of Rh-immune globulin at 28 weeks and again a few days after delivery. Incompatibility occurs if a woman is Rh-negative and her baby is Rh-positive. If the woman is Rh-negative and her baby’s positive, she’ll need the shot. If her baby is Rh-negative, she won’t.
Chorionic Villus Sampling
Chorionic villus sampling is an invasive screening test that involves taking a small piece of tissue from the placenta. It’s usually performed between the 10th and 12th weeks and is used to test for genetic abnormalities, like Down syndrome, and birth defects. There are two types. One type tests through the belly, which is called a transabdominal test, and one type tests through the cervix, which is called a transcervical test.
Testing has some side effects, like cramps or spotting. There’s also a small risk of miscarriage.
Second Trimester Screening Tests
Blood Tests
A quad marker screening test is a blood test conducted during the second trimester. It’s done to test your blood for indications of birth defects, such as Down syndrome. It measures four of the fetal proteins.
A quad marker screening is typically offered if you start prenatal care too late to receive either the serum integrated screening or the sequential integrated screening. It has a lower detection rate for Down syndrome and other birth defects than a sequential integrated screening test or serum integrated screening test.
Glucose Screening
A glucose screening test checks for gestational diabetes. This is usually a condition that can develop during pregnancy. It’s usually temporary. Gestational diabetes can increase your potential need for a caesarean delivery because babies of mothers with gestational diabetes are usually born larger.
What are pathology tests?
A pathology test is a test that examines your blood, urine, faeces or samples obtained by biopsy. Doctors use this information for diagnosis and treatment of diseases and other conditions.
Why are pathology tests important?
Pathology tests help doctors and nurses prevent, diagnose, manage and monitor many conditions, including allergies, infections, chronic diseases and cancer.
Before your test
Follow any instructions given to you about the test. For some tests, you need special preparation such as fasting. Let collection centre staff know if you have not followed the instructions for any reason.
Let your doctor know about any medications you are taking, including herbal or over-the-counter (non-prescription) medications.
If you have other questions about the tests, or are not sure of what you need to do, it is best to check with your doctor or call the pathology collection centre.
Reading the test results
The best person to help you understand your results is the doctor who ordered the test.
Even if the laboratory labels a result as being abnormal, this does not necessarily mean that there is a problem. If you have enough tests done, something will eventually show up as abnormal.
Your doctor will take into account many factors then talk to you about whether an abnormal test result is a sign of a problem, or is just one of those things.
Key points to discuss with your doctor
You might want talk to your doctor about:
which tests are best for you and why,
what you need to do before, during, or after the test,
what the results might mean for your health, such as whether you need any treatment,
whether any abnormal results are important,
whether you will need any follow up tests
More information
The Lab Tests Online website has a number of resources and services available if you need help or more information on pathology testing.
What's a Pap test?
Pap tests find abnormal cell changes in your cervix. How often you get a Pap test depends on your age, medical history, and the results of your last Pap or HPV tests.
What happens during a Pap test?
Pap tests, sometimes called Pap smears, are very important tests for finding abnormal cells on your cervix that could lead to cervical cancer. Pap tests find cell changes caused by HPV, but they don't detect HPV itself.
Pap tests may be part of your regular check up, pelvic exam or well-woman exam. During a Pap test, your doctor or nurse puts a metal or plastic speculum into your vagina. The speculum opens up to separate the walls of your vagina so that they can get to your cervix. Then they use a small sampler — a tiny spatula or brush — to gently collect cells from your cervix. The cells are sent to a lab to be tested.
Pap tests only take a few minutes. They shouldn't hurt, but you might feel some discomfort or pressure when your doctor or nurse opens the speculum inside you. You might also feel a light scratching when they take cells from your cervix.
Do I need a Pap test?
You should start getting regular Pap tests age 21. How often you get tested after that depends on your age, medical history, and the results of your last Pap or HPV tests. In general:
If you’re 21–29 years old, get a Pap test once every 3 years (starting at age 25, your doctor may switch to an HPV test - either one is fine).
If you’re 30–65 years old, get a Pap test and HPV test (co-testing) once every 5 years, or just a Pap test or HPV test every 3 years.
If you’re older than 65, you may not need Pap tests anymore.
You may need to get tested more often if you’ve had problems with your cervix before, have a weak immune system, or if your mother took a medicine called DES while she was pregnant with you. Your doctor or nurse will tell you which tests you need and how often you should get them.
What if I have an abnormal Pap test?
If your Pap test results are abnormal, don’t panic. It's pretty common to have unclear or abnormal Pap test results. Most of the time, it doesn’t mean that you have cervical cancer.
An unclear test result means that your cervical cells look like they could be abnormal. But it isn’t clear if it’s related to HPV or something else. Unclear results are also called equivocal, inconclusive, or ASC-US.
An abnormal Pap test result means that there are abnormal cell changes on your cervix. This doesn’t mean that you definitely have cervical cancer. The changes may be minor (low-grade) or serious (high-grade). The more serious changes are often called precancerous because they aren’t cancer yet but can turn into it over time.
If you have an unclear or abnormal Pap test result, you made need further tests and/or treatment including:
Another Pap test
An HPV test: a test that looks for high-risk types of the virus that can cause precancerous cells
A colposcopy: a special exam to look more closely at your cervix to see if there are precancerous cells.
If your doctor finds abnormal cells during your colposcopy, you’ll probably need treatment. Common treatments include cryotherapy and LEEP.
Where can I go for a Pap test?
You can get a Pap test at your doctor or nurse’s office, a community health clinic, the health department, or your local Planned Parenthood health center.
LDL Cholesterol Test:
What is a Cholesterol Test?
Cholesterol is a waxy, fat-like substance that's found in your blood and every cell of your body. You need some cholesterol to keep your cells and organs healthy. Your liver makes all the cholesterol your body needs. But you can also get cholesterol from the foods you eat, especially meat, eggs, poultry, and dairy products. Foods that are high in dietary fat can also make your liver produce more cholesterol.
There are two main types of cholesterol: low-density lipoprotein (LDL), or "bad" cholesterol, and high-density lipoprotein (HDL), or "good" cholesterol. A cholesterol test is a blood test that measures the amount of each type of cholesterol and certain fats in your blood.Too much LDL cholesterol in your blood may put you at risk for heart disease and other serious conditions. High LDL levels can cause the build-up of plaque, a fatty substance that narrows the arteries and blocks blood from flowing normally. When blood flow to the heart is blocked, it can cause a heart attack. When blood flow to the brain is blocked, it can lead to stroke and peripheral artery disease.
Other names for a cholesterol test: Lipid profile, Lipid panel
What is it used for?
If you have high cholesterol, you may not experience any symptoms at all, but you could be at significant risk for heart disease. A cholesterol test can give your health care provider important information about the cholesterol levels in your blood. The test measures:
-LDL levels. Also known as the "bad" cholesterol, LDL is the main source of blockages in the arteries.
-HDL levels. Considered the "good" cholesterol, HDL helps get rid of "bad" LDL cholesterol.
-Total cholesterol. The combined amount of low-density lipoprotein (LDL) cholesterol and high-density lipoprotein (HDL) cholesterol in your blood.
-Triglycerides A type of fat found in your blood. According to some studies, high levels of triglycerides may increase the risk of heart disease, especially in women.
-VLDL levels. Very low-density lipoprotein (VLDL) is another type of "bad" cholesterol. Development of plaque on the arteries has been linked to high VLDL levels. It's not easy to measure VLDL, so most of the time these levels are estimated based on triglyceride measurements.
Why do I need a cholesterol test?
Your doctor may order a cholesterol test as part of a routine exam, or if you have a family history of heart disease or one or more of the following risk factors:
-High blood pressure
-Type 2 diabetes
-Smoking
-Excess weight or obesity
-Lack of physical activity
-A diet high in saturated fat
Your age may also be a factor, because your risk for heart disease increases as you get older.
What happens during a cholesterol test?
A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.
Cholesterol tests are usually done in the morning, as you may be asked to refrain from eating for several hours prior to the test.
Will I need to do anything to prepare for the test?
You may need to fast--no food or drink--for 9 to 12 hours before your blood is drawn. Your health care provider will let you know if you need to fast and if there are any special instructions to follow.
Are there any risks to the test?
There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
What do the results mean?
Cholesterol is usually measured in milligrams (mg) of cholesterol per deciliter (dL) of blood. The information below shows how the different types of cholesterol measurements are categorized.
A healthy cholesterol range for you may depend on your age, family history, lifestyle, and other risk factors. In general, low LDL levels and high HDL cholesterol levels are good for heart health. High levels of triglycerides may also put you at risk for heart disease.
The LDL on your results may say "calculated" which means it includes a calculation of total cholesterol, HDL, and triglycerides. Your LDL level may also be measured "directly," without using other measurements. Regardless, you want your LDL number to be low.
Is there anything else I need to know about my cholesterol levels?
High cholesterol can lead to heart disease, the number one cause of death in the United States. While some risk factors for cholesterol, such as age and heredity, are beyond your control, there are actions you can take to lower your LDL levels and reduce your risk, including:
-Eating a healthy diet. Reducing or avoiding foods high in saturated fat and cholesterol can help reduce the cholesterol levels in your blood.
-Losing weight. Being overweight can increase your cholesterol and risk for heart disease.
-Staying active. Regular exercise may help lower your LDL (bad) cholesterol levels and raise your HDL (good) cholesterol levels. It may also help you lose weight.
Talk to your health care provider before making any major change in your diet or exercise routine.
LASIK Pretests Before Eye Surgery
While LASIK is generally a safe and effective treatment for several common vision problems, it's not for everyone. If you are considering LASIK, you should undergo a thorough examination by an eye care professional to determine if you are a good candidate for the procedure. The examination should include a thorough discussion of your medical history as well as your lifestyle.
Prequalification Tests Before LASIK Surgery
Besides this detailed examination, the following tests should be performed before determining if you should go forth with surgery.
Comprehensive Vision Analysis: During a comprehensive eye examination, the doctor measures many things about your eyes and vision. However, before a refractive procedure such as LASIK, your doctor should measure your prescription after they use "cycloplegic" eye drops. Besides dilating your eyes, these eye drops temporally paralyze the focusing muscle inside your eye. This allows the doctor to measure your total prescription without allowing you to focus too hard. Basically, it lets the doctor collect the raw data of your true vision.
Binocular Vision Assessment: Although fairly rare, some people have minor eye muscle alignment problems or binocular vision deficits that may interfere with some LASIK results. Patients who may remember being told they had a lazy eye when they were younger may fall into this category. A patient could possibly have one of these ailments and be unaware of it, as their eye muscles tend to hide it well. Also, LASIK is sometimes performed with a monovision method to correct not only distance vision but also close vision. However, this method can sometimes cause double vision or increase eyestrain after having LASIK.
Qualitative and Quantitative Tear Film Tests: Both the quality and quantity of your tears is important when determining if you are a good LASIK candidate. If either of these is not optimal, the doctor may choose to delay LASIK until your tears can be corrected by mechanical or therapeutic measures.
Corneal Topography: Corneal topography is a computerized method of determining the exact topographical shape and power of the cornea. Measurements are computed and placed into color maps. Hotter colors, such as red, show steeper areas, while cooler colors show areas that are flatter. Some patients have a corneal shape that does not bring about problems before LASIK, but it may put them at risk for developing the thcorneal disease, such as keratoconus, after having LASIK.
Wavefront Analysis: Wavefront analysis is a relatively new development in eye care and can be very important to measure higher-order aberrations of the human optical system. Higher order aberrations are types of vision deficits similar to lower order aberrations, such as nearsightedness, farsightedness, and astigmatism, but represent different distortions. They seem to be more apparent in some patients and often cause symptoms such as decreased night vision, glare, and halos around lights.
Corneal Thickness Measurements: Pachymetry is known as the measurement of the thickness of the cornea. This is important for LASIK patients because the procedure changes the power of the eye by reshaping and removing corneal tissue. Patients with extremely thin corneas may not make good LASIK candidates. While today’s methods of performing LASIK make this less of a problem, pachymetry is still vital to the success of any refractive procedure
Accurate Pupil Size Measurements: Nighttime and daytime pupil size is important for quality of vision after LASIK. Patients with naturally large pupils or pupils that dilate heavily in dim light may have more glare, halos, and contrast problems after having LASIK. However, with today's laser systems, this tends to be less of a problem. The size of the zone that is made with lasers today is significantly larger than those made with the first lasers. Also, it was discovered that a de-centered laser ablation zone was to blame for many of these symptoms rather than having too large of a pupil. Nonetheless, pupil size is measured with special devices, such as an infrared pupillometer, so that a better surgical plan can be devised.