Every parent-to-be hopes for a healthy baby, but it can be hard not to worry: What if the baby has a serious or untreatable health problem? What would I do? Is there anything I can do to prevent problems?
Concerns like these are completely natural. Fortunately, though, a wide array of tests for pregnant women can help to reassure them and keep them informed throughout their pregnancies.
Prenatal tests can help identify health problems that could endanger both you and your unborn child, some of which are treatable. However, these tests do have limitations. As an expectant parent, it’s important to educate yourself about them and to think about what you would do if a health problem is detected in either you or your baby.
Why Are Prenatal Tests Performed?
Prenatal tests can identify several different things:
- treatable health problems in the mother that can affect the baby’s health
- characteristics of the baby, including size, sex, age, and placement in the uterus
- the chance that a baby has certain congenital, genetic, or chromosomal problems
- certain types of fetal abnormalities, including some heart problems
The last two items on this list may seem the same, but there’s a key difference. Some prenatal tests are screening tests and only reveal the possibility of a problem. Other prenatal tests are diagnostic, which means they can determine — with a fair degree of certainty — whether a fetus has a specific problem. In the interest of making the more specific determination, the screening test may be followed by a diagnostic test.
Prenatal testing is further complicated by the fact that more abnormalities can be diagnosed in a fetus than can be treated or cured.
What Do Prenatal Tests Find?
Among other things, routine prenatal tests can determine key things about the mother’s health, including:
- her blood type
- whether she has gestational diabetes
- her immunity to certain diseases
- whether she has a sexually transmitted disease (STD) or cervical cancer
All of these conditions can affect the health of the fetus.
Prenatal tests also can determine things about the fetus’ health, including whether it’s one of the 2% to 3% of babies in the United States that the American College of Obstetricians and Gynecologists (ACOG) says have major congenital birth defects.
Tests for Disorders
Categories of defects which can be picked up by prenatal tests include the following disorders:
Dominant Gene Disorders
In dominant gene disorders when one parent is affected, there’s a 50–50 chance a child will inherit the gene from the affected parent and have the disorder.
Dominant gene disorders include:
- Achondroplasia, a rare abnormality of the skeleton that causes a form of dwarfism, can be inherited from a parent who has it, but most cases occur without a family history.
- Huntington disease, a disease of the nervous system that causes a combination of mental deterioration and a movement disorder.
Recessive Gene Disorders
Because there are so many genes in each cell, everyone carries some abnormal genes, but most people don’t have a defect because the normal gene overrules the abnormal recessive one. But if a fetus has a pair of abnormal recessive genes (one from each parent), the child will have the disorder. It can be more likely for this to happen in children born to certain ethnic groups.
Recessive gene disorders include:
- Cystic fibrosis, most common among people of northern European descent, this disease is life threatening and causes severe lung damage and nutritional deficiencies.
- Sickle cell disease, most common among people of African descent, is a disease in which red blood cells form a “sickle” shape (rather than the typical donut shape) that can get caught in blood vessels and damage organs and tissues.
- Tay-Sachs disease, most common among people of eastern European (Ashkenazi) Jewish descent, can cause mental retardation, blindness, seizures, and death.
- Beta-thalassemia, most common among people of Mediterranean descent, this disorder can cause anemia.
X-Linked Disorders
These disorders are determined by genes on the X chromosome. The X and Y chromosomes are the chromosomes that determine sex. These disorders are much more common in boys because the pair of sex chromosomes in males contains only one X chromosome (the other is a Y chromosome). If the disease gene is present on the one X chromosome, the X-linked disease shows up because there’s no other paired gene to “overrule” the disease gene. One such X-linked disorder is hemophilia, which prevents the blood from clotting properly.
Chromosomal Disorders
Chromosomal disorders occur when there is an abnormality in the number or structure of chromosomes, which contain the genetic material. Some chromosomal disorders are inherited but most are caused by a random error in the genetics of the egg or sperm. The chance of a child having these disorders increases with the age of the mother. For example, according to ACOG, 1 in 1,667 live babies born to 20-year-olds have Down syndrome, which causes mental retardation and physical defects. That number changes to 1 in 378 for 35-year-olds and 1 in 106 for 40-year-olds.
Multifactorial Disorders
This final category includes disorders that are caused by a mix of genetic and environmental factors. Their frequency varies from location to location, and some can be detected during pregnancy.
Multifactorial disorders include neural tube defects, which occur when the tube enclosing the spinal cord doesn’t form properly. Neural tube defects, which often can be prevented by taking folic acid (which is in prenatal vitamins) around the time of conception and during pregnancy, include:
- Spina bifida. Also called “open spine,” this defect happens when the lower part of the neural tube doesn’t close during embryo development. The spinal cord and nerves may be covered only by skin, or may be open to the environment, leaving them unprotected.
- Anencephaly. This defect occurs when the brain and head don’t develop properly, and parts of the brain are completely absent or malformed.
Other multifactorial disorders include:
- congenital heart defects
- obesity
- diabetes
- cancer
Who Has Prenatal Tests?
Certain prenatal tests are considered routine — that is, almost all pregnant women receiving prenatal care get them. Other nonroutine tests are recommended only for certain women, especially those with high-risk pregnancies. These may include women who:
- are age 35 or older
- are adolescents
- have had a premature baby
- have had a baby with a birth defect — especially heart or genetic problems
- are carrying more than one baby
- have high blood pressure, diabetes, lupus, heart disease, kidney problems, cancer, a sexually transmitted disease, asthma, or a seizure disorder
- have an ethnic background in which genetic disorders are common (or a partner who does)
- have a family history of mental retardation (or a partner who does)
Although your health care provider (which may be your OB-GYN, family doctor, or a certified nurse-midwife) may recommend these tests, it’s ultimately up to you to decide whether to have them.
Also, if you or your partner have a family history of genetic problems, you may want to consult with a genetic counselor to help you look at the history of problems in your family, and to determine the risk to your children.
To decide which tests are right for you, it’s important to carefully discuss with your health care provider:
- what these tests are supposed to measure
- how reliable they are
- the potential risks
- your options and plans if the results indicate a disorder or defect
Prenatal Tests During the First Visit
During your first visit to your health care provider for prenatal care, you can expect to have a full physical, which may include a pelvic and rectal examination, and you’ll undergo certain tests regardless of your age or genetic background.
You may have a urine test to check for protein, sugar, or signs of infection.
Blood tests check for:
- your blood type and Rh factor. If your blood is Rh negative and your partner’s is Rh positive, you may develop antibodies that prove dangerous to your fetus. This can be prevented through a course of injections given to you.
- anemia (a low red blood cell count)
- hepatitis B, syphilis, and HIV
- immunity to German measles (rubella) and chickenpox (varicella)
- cystic fibrosis. Health care providers now routinely offer this screening even when there’s no family history of the disorder.
Cervical tests (also called Pap smears) check for:
- STDs such as chlamydia and gonorrhea
- changes that could lead to cervical cancer
To do a Pap smear, your health care provider uses what looks like a very long mascara wand or cotton swab to gently scrape the inside of your cervix (the opening to the uterus that’s located at the very top of the vagina). This may be a little uncomfortable, but it is over quickly.
Prenatal Tests Performed Throughout or Later in Pregnancy
After the initial visit, your health care provider will order other tests based on, among other things, your personal medical history and risk factors, as well as the current recommendations. These tests may include:
- Urine tests for sugar, protein, and signs of infection. The sugar in urine may indicate gestational diabetes — diabetes that occurs during pregnancy; the protein can indicate preeclampsia — a condition that develops in late pregnancy and is characterized by a rise in blood pressure, with fluid retention and protein in the urine.
- Group B streptococcus (GBS) infection. GBS bacteria are found naturally in the vaginas of many women but can cause serious infections in newborns. This test involves swabbing the vagina and rectum, usually between the 35th and 37th weeks of pregnancy. If the test comes back positive, it is important to go to the hospital as soon as your labor begins so that intravenous antibiotics can be started in order to reduce the chance of the baby being infected.
- Sickle cell trait tests for women of African or Mediterranean descent, who are at higher risk for having sickle cell anemia — a chronic blood disease — or carrying the trait, which can be passed on to their children.
Other Tests
Here are some other tests that might be performed during pregnancy:
Ultrasound
Why Is This Test Performed?
In this test, sound waves are bounced off the baby’s bones and tissues to construct an image showing the baby’s shape and position in the uterus. Ultrasounds were once used only in high-risk pregnancies but have become so common that they’re often part of routine prenatal care.
Also called a sonogram, sonograph, echogram, or ultrasonogram, an ultrasound is used:
- to determine whether the fetus is growing at a normal rate
- to verify the expected date of delivery
- to record fetal heartbeat or breathing movements
- to see whether there might be more than one fetus
- to identify a variety of abnormalities that might affect the remainder of the pregnancy or delivery
- to make sure the amount of amniotic fluid in the uterus is adequate
- to indicate the position of the placenta in late pregnancy (which may be blocking the baby’s way out of the uterus)
- to detect pregnancies outside the uterus
- as a guide during other tests such as amniocentesis
Ultrasounds also are used to detect:
- structural defects such as spina bifida and anencephaly
- congenital heart defects
- gastrointestinal and kidney malformations
- cleft lip or palate
Should I Have This Test?
Most women have at least one ultrasound. The test is considered to be safe. Some women will have multiple ultrasounds during the pregnancy, others do not have any. Ask your health care provider if he or she thinks you will have ultrasounds during your pregnancy.
When Should I Have This Test?
An ultrasound is usually performed at 18 to 20 weeks to look at your baby’s anatomy. If you want to know your baby’s gender, you may be able to find out during this time — that is, if the genitals are in a visible position.
Ultrasounds also can be done sooner or later and sometimes more than once, depending on the health care provider and the pregnancy. For example, some providers will order an ultrasound to date the pregnancy, usually during the first 3 months. And others may want to order one during late pregnancy to make sure the baby’s turned the right way before delivery.
Women with high-risk pregnancies may need to have multiple ultrasounds using more sophisticated equipment. Results can be confirmed when needed using special three-dimensional (3-D) equipment that allows the technician to get a more detailed look at the baby.
How Is This Test Performed?
Women need to have a full bladder for a transabdominal ultrasound (an ultrasound of the belly) to be performed in the early months — you may be asked to drink a lot of water and not urinate. You’ll lie on an examining table and your abdomen will be coated with a special ultrasound gel. A technician will pass a wand-like instrument called a transducer back and forth over your abdomen. You may feel some pressure as the technician presses on the bladder. High-frequency sound waves “echo” off your body (and the fetus) and create a picture of the fetus inside on a computer screen.
You may want to ask to have the picture interpreted for you, even in late pregnancy — it often doesn’t look like a baby to the untrained eye.
Sometimes, if the technician isn’t able to see a good enough image from the ultrasound, he or she will determine that a transvaginal ultrasound is necessary. This is especially common in early pregnancy. For this procedure, your bladder should be empty. Instead of a transducer being moved over your abdomen, a slender probe called an endovaginal transducer is placed inside your vagina. This technique often provides improved images of the uterus and ovaries.
Some health care providers may have the equipment and trained personnel necessary to provide in-office ultrasounds, whereas others may have you go to a local hospital or radiology center. Depending on where you have the ultrasound done, you may be able to get a printed picture (or multiple pictures) of your baby and/or a disc of images you can view on your computer and even send to friends and family.
When Are the Results Available?
Although the technician can see the images immediately, a full evaluation by a physician may take up to 1 week.
Depending on where you have the ultrasound done, the technician may be able to tell you that day whether everything looks OK. However, most radiology centers or health care providers prefer that technicians not comment until a specialist has taken a look — even when everything is OK.
Glucose Screening
Why Is This Test Performed?
Glucose screening checks for gestational diabetes, a short-term form of diabetes that develops in some women during pregnancy. Gestational diabetes is increasing in frequency in the United States, and may occur in 3 to 8% of pregnancies. Gestational diabetes can cause health problems for the baby, especially if it is not diagnoses or treated.
Should I Have This Test?
Most women have this test in order to diagnose and treat gestational diabetes, reducing the risk to the baby.
When Should I Have This Test?
Screening for gestational diabetes usually takes place at 24 to 28 weeks. Testing may be done earlier for women who are at higher risk of having gestation diabetes, such as those who:
- have previously had a baby that weighs more than 9 pounds (4.1 kilograms)
- have a family history of diabetes
- are obese
- are older than age 25
- have sugar in the urine on routine testing
- have high blood pressure
- have polycystic ovary syndrome
How Is the Test Performed?
This test involves drinking a sugary liquid and then having your blood drawn after an hour. If the sugar level in the blood is high, you’ll have a glucose-tolerance test, which means you’ll drink a glucose solution on an empty stomach and have your blood drawn once every hour for 3 hours.
When Are the Results Available?
The results are usually available within 1 to 2 days. Ask if your health care provider will call you with the results if they are normal or only if the reading is high and you need to come in for another test.
Chorionic Villus Sampling (CVS)
Why Is This Test Performed?
Chorionic villi are tiny finger-like units that make up the placenta (a disk-like structure that sticks to the inner lining of the uterus and provides nutrients from the mother to the fetus through the umbilical cord). They have the same chromosomes and genetic makeup as the fetus.
This alternative to an amniocentesis removes some of the chorionic villi and tests them for chromosomal abnormalities, such as Down syndrome. Its advantage over an amniocentesis is that it can be performed earlier, allowing more time for expectant parents to receive counseling and make decisions. The risks of CVS are higher than with amniocentesis so the risks and benefits of the test must be weighed.
Should I Have This Test?
Your health care provider may recommend this test if you:
- are older than age 35
- have a family history of genetic disorders (or a partner who does)
- have a previous child with a genetic disorder or had a previous pregnancy with a chromosomal abnormality
- have had an earlier screening test that indicates that there may be a concern
Possible risks of this test include:
- approximately 1% risk of miscarriage (the risk is higher with the transcervical method than with the transabdominal method)
- infection
- spotting or bleeding (this is more common with the transcervical method — see below)
- birth defects when the test is done too early in pregnancy
When Should I Have This Test?
At 10 to 12 weeks.
How Is This Test Performed?
This test is done in one of two ways:
- Transcervical. Using ultrasound as a guide, a thin tube is passed from the vagina into the cervix. Gentle suction removes a sample of tissue from the chorionic villi. Some women experience cramping with the removal.
- Transabdominal. A needle is inserted through the abdominal wall with ultrasound guidance, and a sample of the chorionic villi is removed. Cramping may be felt with this approach as well.
After the sample is taken, the doctor may check the fetus’ heart rate. You should rest for several hours afterward.
When Are the Results Available?
Usually 1 to 2 weeks depending on what the test is being used to look for.
source: http://kidshealth.org/parent/pregnancy/pregnancy/prenatal_tests.html#