Pregnancy: First Trimester (Up to 12 weeks)
At the time of the first prenatal visit, which often takes place during the first trimester of pregnancy, a healthcare practitioner may order several or most of the tests described below to check for certain conditions and infections that could harm the unborn baby or affect the mother’s health during the pregnancy.
Pregnancy Test (hCG)
If pregnancy is only suspected, or if the pregnancy test was not performed by a healthcare practitioner (for example, was instead performed with an at-home urine pregnancy test), then a pregnancy test may be done to confirm that a woman is pregnant.
Pregnancy tests measure human chorionic gonadotropin (hCG), a hormone that is produced by the placenta when a woman is pregnant. The amount of hCG produced during pregnancy increases steadily during the first trimester (8-10 weeks) of a normal pregnancy, peaking around the 10th week after the last menstrual cycle.
There are two types of hCG tests: qualitative and quantitative.
- Qualitative tests can be done on either urine or blood; they are usually done after a missed menstrual period to confirm that the woman is indeed pregnant.
- Quantitative tests measure the actual level of hCG and are performed on blood samples. Some laboratories may have targets for what the hCG level should be for each week of gestation during the first trimester, but each woman’s levels may vary (and the exact gestational age may be uncertain). The most important feature of hCG during the first trimester is that the levels should essentially double every two or three days. If there is any concern about the pregnancy, the patient’s healthcare practitioner will often measure quantitative hCG levels several times to make sure that they are increasing at an appropriate rate.
If hCG levels are not rising normally, the cause may be an ectopic pregnancy (in which the pregnancy is occurring within the tube that leads from the ovary to the uterus or, more rarely, in the abdominal cavity) or an abnormal intra-uterine pregnancy. Ectopic pregnancy may become a medical emergency, so practitioners may need to perform vaginal ultrasound in patients whose hCG is not rising appropriately to make sure that there is a gestational sac within the uterus.
Blood Typing and RBC Antibody Screen
Blood typing is usually done during the first trimester or the first prenatal visit. It is used to determine a pregnant woman’s blood group, to establish whether she is A, B, AB, or O, and whether she is Rh-positive or Rh-negative. A pregnant woman should know her blood type. [See Blood Typing for more information on how this is performed.]
Blood typing is especially important during pregnancy because a mother and her fetus could be incompatible. For example, if the mother is Rh-negative but the father is Rh-positive, the fetus may inherit the Rh antigen from the father and be Rh positive. If the blood types of mother and baby are different, as in this example, the mother may produce antibodies (antiglobulins) that react with antigens (proteins or factors) on the fetus’ red blood cells. The antibodies may cross the placenta and cause destruction of the baby’s red blood cells, resulting in a serious condition referred to as hemolytic disease of the newborn (HDN). Although the first Rh-positive baby is unlikely to become ill, the antibodies produced during that first pregnancy may affect subsequent Rh-positive babies.
To greatly reduce the likelihood that an Rh-negative mother will develop this antibody, she may be treated with an injection of Rh immune globulin at approximately 28 weeks’ of pregnancy. The Rh immune globulin binds to and “masks” the fetus’s Rh antigen and prevents the mother from developing antibodies against the Rh antigen. Additional injections may be necessary during the pregnancy if she has an amniocentesis, chorionic villus sampling, or an abdominal injury, and after delivery if the baby is Rh-positive. Before each injection is given, an antibody screen is performed to make sure that the woman has not already developed Rh antibodies.
In addition to Rh-negative women who have had an Rh-positive baby, any woman who has had a blood transfusion or had prior pregnancies may produce an antibody to blood factors other than Rh that can potentially harm an unborn baby. An antibody screen done during the first trimester and repeated during the third trimester (between 28 and 29 weeks of pregnancy) determines if potentially harmful antibodies are present in the mother’s blood. If a harmful antibody is detected, the baby’s father should be tested, if possible, to see if his RBCs have antigens that the mother’s antibody could target. If so, then the fetus’ RBCs may also have antigens that may be targeted. In this case, the healthcare practitioner will likely monitor the mother’s antibody level and the health of the fetus for the duration of the pregnancy. Signs that the fetus is becoming ill may necessitate treatment before birth (such as an intrauterine transfusion) or an early delivery.
Although Rh incompatibility has more severe consequences, one of the most common causes of HDN is actually an incompatibility between the mother’s and baby’s ABO blood groups, not the Rh factor. However, the RBC antibody screen cannot be used to predict whether HDN will occur because antibodies to the ABO blood groups are naturally-occurring.
Pap Test and HPV Testing
A Pap test is used to screen a woman’s cervix (the opening to the uterus) for cancer, pre-cancerous changes, inflammation, and some sexually transmitted diseases. HPV testing detects the high-risk types of the human papillomavirus, which increase a woman’s risk of cervical cancer. Several health professional organizations recommend the following:
- Screening with Pap tests should begin no earlier than age 21.
- Women between the ages of 21 and 30 should have a Pap test every 3 years.
- Women between the ages of 30 and 65 should have both a Pap test and an HPV test every 5 years (preferable); a Pap test alone every 3 years is also acceptable.
In most cases, if a woman has a negative HPV test and/or normal Pap test within the recommended interval, she will not require the tests when she becomes pregnant. If it has been more than the recommended time interval since the last cervical cancer screen, or if there are any questions about the status of the cervix, the healthcare practitioner may suggest screening pre-conception or at the beginning of the pregnancy.
Early detection of high-risk types of HPV, abnormal cervical cells, and infections and early treatment, if necessary, offer the best chance to prevent any problems from progressing and potentially affecting the health of the baby and the success of the pregnancy.
Urine Screen for Glucose and/or Protein
At each prenatal visit through the first, second, and third trimesters, the expectant mother may be asked to give a urine specimen, which will usually be tested in the office using a dipstick to screen for the presence of glucose (sugar) and/or protein. Although small amounts of both glucose and protein are normally present in urine, high levels can indicate a problem and may call for further testing.
A high level of protein in the urine is a warning sign. It may indicate kidney damage or disease or it may be a transient elevation due to, for example, an infection, medication, or emotional or physical stress. Examples of additional tests that may be done to help determine the cause include a 24-hour urine protein test, full urinalysis, or urine culture (to identify any bacteria or yeast present).
Of particular concern during the second and third trimesters is preeclampsia (sometimes called toxemia or pregnancy-induced hypertension), a disorder characterized by high blood pressure and large amounts of protein in the urine that occurs in approximately 8% of all pregnancies. Symptoms include swelling, sudden weight gain, headache, and vision changes. Risk factors include first pregnancy, being pregnant with more than one child, age (teenagers and women over 40 years of age), being African American, and having pre-existing diabetes, hypertension, or kidney disease. It can result in a decrease of air and nutrition getting to the baby through the placenta, causing low birth weight or other complications. If caught early enough, however, through routine checking of blood pressure and urine protein levels, health problems for the mother and baby due to pre-eclampsia can be managed.
High urine glucose levels may be a sign of undiagnosed diabetes that is already present in the mother or gestational diabetes, a form of diabetes that can develop during pregnancy. A positive urine test for glucose will usually be followed by a confirmatory blood glucose test, which is also routinely used to screen for gestational diabetes during the second trimester (between 24 and 28 weeks of pregnancy).
Complete Blood Count (CBC)
The complete blood count (CBC) is a test that evaluates the cells that circulate in blood. Blood consists of three types of cells suspended in fluid called plasma: red blood cells (RBCs), white blood cells (WBCs), and platelets (PLTs). To identify and prevent problems, a CBC may be done before pregnancy, if possible, at the beginning of pregnancy, and one or more times during pregnancy. The first baseline results can be compared to later values to look for changes that could indicate a health issue.
- Red blood cells contain hemoglobin, a protein that gives blood its red color. It binds to oxygen in your lungs, transports it throughout the body, and releases it to the cells and tissues. During pregnancy, a woman’s hemoglobin must transport enough oxygen to meet both her and her fetus’ needs. If a woman has insufficient RBCs and/or hemoglobin, she is said to be anemic.Many pregnant women will experience some degree of anemia. While mild anemia can make you feel tired and weak, more severe anemia in a pregnant woman can cause a fetus to receive too little oxygen to support normal development.
All women lose a small amount of blood during delivery. Although this is usually not a problem, even a small amount of blood loss can be harmful to women with anemia. A healthcare practitioner may want to know the level of hemoglobin in a pregnant woman’s blood before delivery to assess the possible impact of the expected blood loss.
- White blood cells help protect the body from infections and also have other immune functions. Evaluating WBCs during a woman’s pregnancy can help detect infections so that they may be treated and resolved before they cause significant health problems in the mother or her baby.
- Platelets are special cell fragments in the blood that help form clots to stop bleeding. Women with low platelet counts, or who have platelets that don’t function properly to form clots, are at risk of life-threatening bleeding during delivery. Follow-up testing may be needed to help determine treatment options if a platelet problem is detected.
Immunity to Rubella (German Measles)
Rubella is caused by a virus that is passed from person to person by coughs or sneezes. Any contact with the nasal or throat secretions of an infected person can spread the virus. Women who have either had a rubella infection or have received the vaccination will have an antibody in their blood that will usually prevent them from getting the infection a second time. This antibody also protects the unborn baby against the virus; this protection is called immunity.
Rubella infections during childhood usually cause mild symptoms. However, if a woman becomes infected with rubella during the first 3 months of her pregnancy and does not have immunity to the virus, the baby is at risk of having serious birth defects.
All women considering a first-time pregnancy or those who are pregnant for the first time should be tested to see if they have this immunity. A blood specimen is tested to see if a sufficient amount of antibody is present in the blood to protect the pregnant woman and the fetus. If a woman does not have enough antibodies and is not currently pregnant, she may be given a rubella vaccination. She should then wait at least 28 days before becoming pregnant.
The rubella vaccine is a weakened form of a live virus and should not be given to a woman who is currently pregnant. If a pregnant woman does not have sufficient antibody to protect her and her baby, she will be advised by her healthcare practitioner to avoid contact with anyone who has symptoms of rubella throughout the rest of her pregnancy. She should consult with her healthcare provider about the best time to get vaccinated after her baby is born and follow through with getting a rubella vaccination so that her next baby will be protected.
Human Immunodeficiency Virus (HIV)
Testing for human immunodeficiency virus (HIV) infection has become routine prenatal care in the United States. Some states even require that all pregnant women and/or their newborns be tested. Treatment begun during pregnancy can prevent the disease in the child and improve the mother’s health as well. Even so, not all women receive routine prenatal care or are offered the test during pregnancy, acknowledges the U.S. Centers for Disease Control and Prevention (CDC), and some women do not agree to have the test. Ideally, the woman will have the blood test as part of her pre-conception care or early in the pregnancy. This best protects the mother and baby.
- Screening the mother: All pregnant women in the United States should be counseled about HIV early in their pregnancy and receive voluntary HIV testing to protect the child’s health. This is the recommendation of many groups, including the U.S. Public Health Service, American Academy of Pediatrics, American College of Obstetricians and Gynecologists, and U.S. Preventive Services Task Force. Repeating the test in the third trimester is of value to those at high risk for HIV infection.
- Screening the baby: In the United States, if the mother’s HIV status is not determined before or during pregnancy or during labor and delivery, healthcare practitioners recommend that the newborn be given an HIV test within 24 hours of the birth (in a few states, this is a requirement; see Newborn Screening). Treatment begun within 48 hours of birth helps prevent a baby who was exposed to the virus from becoming infected.
HIV is the virus that causes AIDS (acquired immunodeficiency syndrome). If a pregnant woman is infected with HIV, the virus can be passed to and infect her baby.
The screening tests detect HIV antigen (p24) and/or HIV antibodies in the blood. The combination HIV antibody and antigen test is the recommended screening test for HIV. It is available only as a blood test. By detecting both antibody and antigen, the combination test increases the likelihood that an infection is detected soon after exposure. Some screening tests detect only HIV antibody. These tests are available as blood tests or tests of oral fluid.
If the screening test is positive, it must be followed by a second antibody test that is different than the first test. If the second test does not agree with the first test, then a third test is performed that detects the genetic material (RNA) of the virus.
If a woman’s confirmatory tests indicate an HIV infection, she will want to consult with her healthcare provider before becoming pregnant about the risks of infecting a baby and the effects of the pregnancy on her health. Treatment of HIV-infected mothers during pregnancy, precautions at birth, and avoiding breast-feeding can minimize the risk of passing the infection from mother to child. Giving the antiretroviral drug zidovudine intravenously during labor and delivery and also to the newborn twice a day by mouth for 6 weeks reduces the rate of transmission from 25-33% to about 1-2%. A combination of antiretroviral therapies is most effective at reducing the risk of HIV transmission to the baby.
A negative test for the antibody to HIV may mean that there is no infection or that a sufficient amount of the antibody has not yet been produced to be detected. If a woman participates in high-risk activities that may transmit HIV, such as unprotected sexual contact or intravenous drug use, she should be retested one or more additional times during the pregnancy.
Gonorrhea, Chlamydia, and Syphilis
Gonorrhea, chlamydia, and syphilis are three common sexually transmitted diseases (STDs) caused by bacterial infections. In a pregnant woman, these diseases can lead to a miscarriage or infect the baby before or during delivery. The baby may then have serious health issues such as infections of the eye, joints, or blood; blindness; or breathing problems. Some of these problems are life-threatening. The woman’s health is also endangered by an STD. The best approach is for the woman to receive antibiotics to help clear up the bacterial infection before the pregnancy or before delivery.
All women in the United States should be tested for these STDs before planning a pregnancy and early in their prenatal care, such as during their first prenatal visit. If a woman engages in high-risk activities during her pregnancy, such as unprotected sexual contact, or is otherwise at risk (for example, because she is less than 25 years old), retesting for STDs later in the pregnancy is advised.
Chlamydia and gonorrhea tests detect the actual bacteria in the sample. Some tests use a urine sample or cervical swab. If the test is positive, the person has a current STD infection that requires treatment.
The syphilis test is a blood test. It detects an antibody produced by the body in response to the infection. The test does not distinguish between a current or past infection and, if it is positive, confirmatory testing will be required. A negative test result usually means that the woman is not currently infected; however, it is possible that an infection is too new to detect. Some states require all women to be screened for syphilis during delivery.
Many women and men do not know when they have an STD, and some health care providers do not routinely screen for STDs, the U.S. Centers for Disease Control and Prevention (CDC) acknowledges. Tests for some STDs should be offered routinely during prenatal care because early treatment lowers the chance that the baby also will contract the disease. Other STDS of concern during pregnancy are hepatitis B and hepatitis C and human immunodeficiency virus (HIV). Screening for each of these should also be part of the first prenatal visit, say the 2010 guidelines published by the CDC.
Be sure to ask when planning a pregnancy, at an early prenatal visit, and again in the third trimester about the STD tests appropriate for you and your sexual partner at that time.
Hepatitis B and Hepatitis C Screening
Infection with hepatitis viruses causes inflammation of the liver. People with acute hepatitis B or hepatitis C may have symptoms such as fatigue, nausea, and jaundice. Most people will get better without any intervention, but some may develop a chronic infection. Some of those chronically infected will have progressive liver damage that can lead to liver cancer and death.
Hepatitis B: the hepatitis B screening test is called hepatitis B surface antigen. It detects a protein produced by the virus and can detect a hepatitis B infection even before it causes symptoms. If a woman who is considering getting pregnant tests positive for hepatitis B, she should talk to her healthcare practitioner about how long she should wait to allow the infection to resolve before becoming pregnant.
It is important to detect active hepatitis B infections in pregnant women because newborns are especially vulnerable to developing chronic infection; up to 90% of those who become infected with hepatitis B in utero will become carriers. If a hepatitis infection is detected in a pregnant woman, she can be monitored and the baby can receive treatment at birth to minimize the risk of it developing hepatitis B.
A negative test for the virus means either that there is no current infection or there is not yet a sufficient amount of the antigen to be detected. If a woman participates in high-risk activities that may transmit the hepatitis B virus (such as unprotected sexual contact or intravenous drug use), retesting later in the pregnancy is generally advised.
Hepatitis C: though not common, hepatitis C can be passed from a mother to her baby. Screening of pregnant women is not routine but may be done if the mother is at risk of infection. Risk factors for hepatitis C include abusing intravenous drugs or having a sexual partner who abuses intravenous drugs, having a history of multiple sexually transmitted diseases, and being infected with hepatitis B.
Antibody tests are used to screen for the infection. Since the antibody test can remain positive in most people even if they have cleared the infection, a positive antibody test is followed by a hepatitis C RNA test, which detects genetic material of the virus. A positive result on the RNA test means the virus is present, the infection has not resolved, and the person may require treatment. The hepatitis C genotype test determines which type of virus is present to help guide treatment.
Urine Culture for Asymptomatic Bacteriuria
Several organizations, including the U.S. Preventive Services Task Force (USPSTF), the Infectious Diseases Society of America (IDSA), the American Academy of Family Physicians (AAFP), and the American College of Obstetricians and Gynecologists (ACOG), recommend that pregnant women be screened for asymptomatic bacteriuria using a urine culture between 12 and 16 weeks gestation or at the first prenatal visit, if later (ACOG recommends first prenatal visit and repeated in the third trimester).
Asymptomatic bacteriuria in pregnancy is diagnosed when significant amounts of bacteria are found by urine culture but the woman is not experiencing any symptoms associated with a urinary tract infection, such as pain or urgency to urinate. This condition occurs in approximately 2%-10% of pregnant women in the U.S. and can lead to more serious kidney infection as well as increases the risk of preterm delivery and low birth weight. Treatment with appropriate antibiotics is advised.
Blood Glucose or Hemoglobin A1c Testing for women at risk of type 2 diabetes
Sometimes a healthcare practitioner will screen for pre-existing diabetes in a pregnant woman at the first prenatal visit or during the first trimester, especially if the woman has risk factors for diabetes, such as family history. This is different than diabetes that develops during pregnancy (gestational diabetes), which is routinely screened for in the second trimester.
A fasting blood glucose, a 2-hour glucose tolerance test, or a hemoglobin A1c may be used for identifying pre-existing diabetes in pregnant women. (See the article on Glucose Tests for more details.) An elevated level of blood glucose may mean that the woman has diabetes. She will receive additional testing to confirm the diagnosis and, if diagnosed, will receive treatment to manage the condition.
A different set of tests is used to diagnose gestational diabetes.
Thyroid Stimulating Hormone (TSH) for women with history of thyroid disease
Pregnancy causes normal changes in the function of many endocrine glands, but it has a marked effect on the thyroid gland, which produces hormones such as thyroxine (T4) and triiodothyronine (T3) that are critical to the healthy development of a fetus as well as the health of the mother.
Women with known thyroid conditions will usually require careful monitoring if they become pregnant. A healthcare practitioner may use tests for thyroid stimulating hormone (TSH) to monitor a woman’s thyroid function throughout her pregnancy. TSH is produced by the pituitary, a small gland in the brain, in response to low T4 or T3 levels. Increased TSH levels in women who are taking thyroid hormone replacement may mean that their dose of hormone replacement needs to be increased.
Some have advocated screening pregnant women during the first trimester (or even before pregnancy) for elevated TSH even if they do not have a history of thyroid disease. This is because a significant percentage of women may have an underlying thyroid disorder that is unsuspected and that will cause problems during pregnancy. However, most guidelines do not recommend this as being necessary.
TORCH panel if exposure or infection is suspected
The TORCH panel is used to screen for certain infectious diseases that can cause birth defects in a baby if the mother contracts them during the pregnancy. The blood tests that make up the panel are for:
- Cytomegalovirus (CMV)
- Herpes simplex virus (HSV)
Some of these are ordered individually, either before or early in pregnancy; the complete TORCH panel is less commonly ordered since more specific and sensitive tests to detect these infections are available.
Other infections that may be tested at the same time include syphilis, hepatitis B, coxsackie virus, Epstein-Barr virus, varicella zoster virus, and parvovirus B19.
Varicella Zoster Virus (Chickenpox) to check for immunity (less routine)
Varicella zoster virus (VZV) causes the illnesses known as chickenpox and shingles. Although most pregnant women have already been exposed to the virus and therefore are immune, some may not have had the infection or been immunized. Since the virus can cause birth defects or illness in the baby (depending on when during the pregnancy an infection occurs), testing for VZV is available before or early in pregnancy to determine if the woman has antibodies to VZV.
If a woman is already pregnant, she cannot receive the vaccine for VZV and should avoid being exposed to anyone who has chickenpox or shingles. If it is determined that a pregnant woman may have been exposed to the virus, treatment is available that can prevent or weaken the severity of the illness.
Bacterial Vaginosis Screen if a woman has symptoms
Bacterial vaginosis (BV), an overgrowth of a normal flora in the vagina that causes a vaginal discharge, is relatively common in both pregnant and non-pregnant women. Untreated bacterial vaginosis during pregnancy can result in amniotic fluid infection, premature rupture of the membranes, premature delivery, low birth weight of the baby, and possibly pelvic inflammatory disease in the mother. Healthcare practitioners do not perform this test routinely but may order it for those who have symptoms, especially if the woman previously delivered a premature baby.
Signs and symptoms of bacterial vaginosis may include the following:
- Vaginal discharge that is not clear in appearance
- Presence of “clue cells,” which are vaginal epithelial cells with most of the surface covered by bacteria, in a sample of vaginal discharge that is examined under a microscope
- Amine (fishy) odor when the discharge is tested with a chemical
- A decrease in acidity of the vaginal discharge
If the woman has 3 of these 4 signs and symptoms, she is diagnosed with bacterial vaginosis. It is usually cured with a 7-day treatment of a prescribed antibiotic.
Tests for Fetal Abnormalities
First Trimester Screening
It is possible during the early stages of pregnancy to estimate the possibility of a mother having a baby affected by Down syndrome using blood tests, sometimes in combination with ultrasound measurements. These tests may also indicate the possibility of other chromosome disorders, such as Edwards syndrome. This type of screening provides an opportunity to assess the possibility of these conditions being present without performing more invasive procedures, such as chorionic villus sampling or amniocentesis. Only those women whose screening results indicate that they are in a higher risk group are currently counseled about having further tests.
First trimester screening is usually performed between 11 and 14 weeks of pregnancy and includes the measurement of blood levels of pregnancy associated plasma protein A (PAPP-A) and either free or total human chorionic gonadotrophin (hCG). In addition, an ultrasound scan called nuchal translucency is done. This involves taking a measurement of the thickness of the skin and tissue at the back of the baby’s neck. The results from these tests will be combined and used to calculate the chance of the baby having Down syndrome or other chromosome abnormality.
Cell-free Fetal DNA
Also known as: Noninvasive prenatal testing (NIPT) or noninvasive prenatal diagnosis (NIPD)
Cell-free fetal DNA (cffDNA) testing is a non-invasive maternal blood test that can assess the risk of a pregnant woman’s developing baby (fetus) having certain chromosome disorders early in pregnancy. The test requires only a blood draw from a pregnant woman’s arm and can be done as early as the 10th week of pregnancy, with results available in about one week. The blood sample is evaluated for fetal cell-free genetic material that circulates in the mother’s blood.
Currently, the test primarily screens for three disorders in a developing baby resulting from the presence of an extra chromosome (trisomies): Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13). It may also be used to identify other rare conditions resulting from an extra chromosome or missing piece of chromosome (microdeletion).
Studies of cffDNA have shown an ability to recognize 98% of cases of Down syndrome, with a false-positive rate of less than 0.5%. The current first trimester screen only assesses risk of Down syndrome and Edwards syndrome, whereas cffDNA screens for three trisomy disorders with the potential for more.
The American College of Obstetricians and Gynecologists (ACOG) recommends that pregnant women discuss the risk and benefits of prenatal screening with their healthcare practitioners and/or a genetic counselor. Conventional screening such as second trimester maternal serum screening remains the best choice for women with a low risk of having a baby with a chromosome disorder, says ACOG. However, any woman may choose to have cffDNA testing done regardless of her risk.
ACOG recommends that cffDNA testing be offered, after pre-test genetic counseling, to pregnant women at increased risk. They include women age 35 and older, women with a history of a pregnancy with a child with a trisomy, and women carrying a fetus with ultrasound findings indicating increased risk.
Women should make this choice with a thorough understanding of the limitations of the test. CffDNA will detect only the most common trisomies. False-positives and false-negatives do occur. A negative result does not necessarily mean that a woman will have an unaffected child. Women with positive cffDNA results should be referred for genetic counseling and be offered chorionic villus sampling (CVS) or amniocentesis to confirm the diagnosis.
Chorionic Villus Sampling
This test is not routinely performed but may be discussed with or offered to women who are at an increased risk of having a baby with certain chromosomal or genetic abnormalities.
Between the tenth and twelfth week, a chorionic villus sampling (CVS) procedure can be performed in which either a needle inserted through the woman’s abdomen or a tube inserted through the woman’s vagina and cervix is used to obtain a tissue sample from the placenta. These cells have the same genetic makeup as the fetus and are analyzed for chromosomal disorders, such as is seen in Down syndrome, and gene abnormalities that cause metabolic disorders, such as Tay-Sachs and cystic fibrosis.
Any of the following are the usual indications for this diagnostic procedure:
- An earlier screening test gives a reason for concern
- The pregnant woman is 35 years of age or older
- There is a strong family history of a specific genetic disorder (in either biological parent)
- Both biological parents possess a gene for an inherited disorder
- A previous child of one of the biological parents had a birth defect
Carefully chosen screening tests may help the woman avoid this diagnostic procedure, which is associated with a risk of miscarriage and infection.
(©2015) Stanford Children’s Health. For Your Health. Available online at http://www.stanfordchildrens.org/en/health-topics?. Accessed October 2015.
(©January 2014) American College of Obstetricians and Gynecologists. Pregnancy, Frequently Asked Questions. Available online at http://www.acog.org/-/media/For-Patients/faq133.pdf?dmc=1&ts=20150917T1442554275. Accessed October 2015.
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(June 29, 2015) American Academy of Pediatrics. Tests and Screenings during Pregnancy. Available online at https://www.healthychildren.org/English/ages-stages/prenatal/Pages/Tests-During-Pregnancy.aspx. Accessed October 2015.
(March 2015) March Of Dimes. Prenatal Tests. Available online at http://www.marchofdimes.org/pregnancy/prenatal-tests.aspx. Accessed October 2015.
(July 31, 2015) Centers for Disease Control and Prevention. Preconception Health and Health Care, Information for Health Professionals. Available online at http://www.cdc.gov/preconception/hcp/index.html. Accessed October 2015.
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For additional sources, see the overview article on Pregnancy.