Hemoglobin (HGB) and Hematocrit (HCT)
What it measures. These two tests are used to screen for anemia in pregnancy. Anemia

exists when there are not enough red blood cells (RBCs) to meet the oxygen needs of the body. Hemoglobin measures the number of RBCs present in a sample of blood, and HCT measures the percentage of RBCs in the blood. The HGB and HCT are checked at the beginning of the pregnancy and again in the third trimester.

What it tells you. Pregnant women are often slightly anemic compared with nonpregnant women, and this is usually normal. The mother's blood volume increases during the pregnancy to meet the needs of the growing baby and uterus. As it does, the plasma (fluid part of the blood) expands by 50%, and the RBCs expand by only 30%. The net result is that the blood is diluted slightly, which makes for a lower HGB and HCT. If anemia is present, these tests can indicate if it is mild or severe. However, anemia can have many causes, including inadequate iron stores, an inherited blood disorder, or other rare health problems. The tests won't tell you the type of anemia. Further tests will be ordered to clarify the cause and how best to treat it.

Red Blood Cell Indices: Mean Corpuscular Volume (MCV); Mean Corpuscular Hemoglobin (MCH); Mean Corpuscular Hemoglobin Concentration (MCHC) Measures
What it measures. The red blood cell indices measure specific characteristics of the RBC. Mean corpuscular volume is the average volume of the RBC; MCH is the weight of the RBC; and MCHC is the proportion of the RBC volume that comes from the hemoglobin.

What it tells you.These tests can help to determine the possible causes of anemia. Normal RBC indices combined with a low HGB and HCT may indicate iron-deficiency anemia.

 
White Blood Cells: WBCs and WBC Differentia
What it measures. White blood cells (WBCs) are an important part of the body's immune system. There are different types of WBCs, and the WBC differential counts the percentage of each type.

What it tells you. An elevated WBC count might indicate that the body is fighting some kind of infection, usually bacterial in nature. There are many other, less common, causes for both high and low WBC counts. The test alone does not tell you the cause of these abnormal levels. The differential might give further clues as it shows which types of WBCs are active.

 
Platelet Count
What it measures. Platelets are the blood component responsible for your ability to clot blood when you bleed. The platelet count test measures the number of platelets in the blood sample. Since it is normal to have bleeding after the birth, it is very important to be able to clot blood.

What it tells you. This test will tell you if you have the normal number of platelets. If they are low, it will be important to determine why and to watch platelet levels closely during pregnancy. If they are high (which is rare), further tests might be ordered to determine the cause.

 
Blood Type
What it measures. The test determines your specific blood type: O, A, B, or AB. In the U.S., 46% of the population have type O, 41% have type A, 9% have type B, and 4% have type AB.
What it tells you. This is important information to know if you ever need a blood transfusion. Also, if the father of the baby has a different blood type than you, the baby may have a different type as well. In most cases, this is not a problem. Occasionally something called ABO Incompatibility occurs, such as when the baby is A, B, or AB, and the mother has a different blood type. In this case, the infant has an increased risk of getting jaundice in the early newborn period.

 
Rh Factor
What it measures. Rh Factor refers to the Rhesus factor in the blood. If a certain group of factors are absent, you are Rh-negative. If they are present, you are Rh-positive.

What it tells you. If you and the father of the baby are Rh-negative, the baby will also be negative - and there will be no problem. If mom is Rh-positive and the baby is negative, it will again be fine. However, if the mom is negative and the baby is positive, there will be a risk for sensitization - where the mother's blood makes antibodies against the baby's blood.

 
HIV
What it measures. The HIV test screens for the presence of antibodies to the human immunodeficiency virus, which can lead to autoimmune deficiency syndrome (AIDS). HIV can be transmitted to the baby.

What it tells you. The test most accurately reflects exposures that occurred over six months prior to the test. If you have been exposed to the virus more recently than that, the test might show a false negative, because you don't yet have enough antibodies to detect the virus. Test again six months after a negative test result if you are at risk.

 
Antibody Screen
What it measures. The antibody screen checks for the presence of antibodies to other blood types in the mother's blood. This test is done on all mothers at the beginning of their care. For Rh-negative mothers, it will also be repeated at 28 weeks.
What it tells you. If you are Rh-negative, the test determines whether you have ever been sensitized against another blood type. It does not tell you when or how that sensitization occurred. Antibodies against Rh-positive could attack infant blood cells when the two blood supplies connect during birth. This causes a breakdown of those cells, called hemolysis. Broken-down red blood cells release bilirubin, which causes jaundice. Too much bilirubin at once can make the baby sick, and he or she will require additional medical care.

 
Rubella Titer
What it measures. Rubella, also called German measles, is a virus. This test determines whether antibodies to the virus are present, and how many. A positive antibody titer means you have antibodies (immune), a negative means you don't (non-immune). It is possible to have an equivocal (indecisive) result, in which case you will be treated as if you are non-immune. If a mother gets rubella during pregnancy, there can be very serious effects on the baby.

What it tells you. The test will tell you if you have been previously exposed to rubella. Most people are immune to rubella because they received childhood vaccinations to prevent it. If they had rubella, they would also be immune. However, it is important to remember that vaccinations do not guarantee permanent immunity, and even someone who was vaccinated can become non-immune. If you are non-immune during your pregnancy, you will be cautioned to avoid any possible exposure to the measles, and your provider will recommend rubella vaccine for you after the baby is born.

 
VDRL and RPR Titer
What it measures. The Venereal Disease Research Laboratory (VDRL) and the rapid plasma reagin (RPR) tests measure for the presence of antibodies to syphilis. Syphilis is a sexually transmitted infection, and can have devastating effects on both the mother and the baby.

What it tells you. The test can tell you if you have been exposed to syphilis. However, the antibodies measured can sometimes be present in response to other illnesses, which means there can be false positives. Therefore, the tests are used for screening only. If these initial tests show the presence of antibodies, then secondary tests that look for the presence of Treponema pallidum - the organism that causes syphilis - will be ordered. A diagnosis cannot be made without multiple tests proving positive.

 
Hepatitis B, Hepatitis C
What it measures. There are two different tests that measure for antibodies to the hepatitis B and C viruses. Hepatitis B and C can seriously affect the mother's health and, depending on the viral count of the mother, can be transmitted to the baby at birth.

What it tells you. The presence of antibodies can indicate that you have been exposed to the virus. It will not tell you when you were exposed, nor if you actually had or have an active form of the illness. Further testing can check for active hepatitis and determine if your liver function has been affected.

 
Wet Mount
What it measures. A wet mount is a slide taken from swabbing the walls of the vagina. It might be done routinely in pregnancy. It tests for the possibility of an overgrowth of normal vaginal yeast and bacteria, and it can also detect certain signs of infections. A wet mount is usually performed in response to a woman's complaints about itching, vaginal burning, and unusual discharge.

What it tells you. Most commonly, the wet mount is used to determine if there is an overgrowth of yeast in the vagina (a yeast infection) or an overgrowth of bacteria called bacterial vaginosis - which has been associated with an increased risk for preterm labor. The wet mount can also be done throughout the pregnancy if the woman has a history of premature labor.

 
Urinalysis
What it measures. There are two versions of urinalysis: a sample sent to a lab for analysis, and a "dipstick" version done at the location of the prenatal visit. This second version will be repeated at every prenatal visit. Both tests check for the presence of protein, sugar, ketones, WBCs, RBCs, and nitrites in the urine. The test sent to the lab can also detect the presence of bacteria. When a urinalysis suggests the presence of bacteria, a urine culture will be performed to give information on the specific bacteria, the number of organisms present, and which antibiotics will be the most useful for treatment.

What it tells you. No abnormal urine test is conclusive, and often the presence of small amounts of these elements are normal. Further tests would be needed to diagnose the possible problem. The main reasons urine is tested are: A large amount of protein is one possible symptom of pregnancy-induced hypertension (PIH), which is also known as pre-eclampsia or toxemia; a large amount of sugar might indicate diabetes; ketones in the urine indicate the body is rapidly breaking down fat stores, and high ketone levels are toxic for the mother and the baby; and WBCs, RBCs, nitrites, and bacteria might be signs of a urinary tract infection (UTI) or a kidney infection. UTIs in pregnancy can lead to serious problems, such as kidney infections and premature labor.

The accuracy of the test can easily be affected by contamination, in which other bacteria that were not actually from the woman?s urinary tract get into the sample. In addition, if not refrigerated properly during transport, an abnormally high number of organisms can grow?making it look like there is an infection when there is not (false-positive).The best indication of a true infection is when WBCs, nitrites, and sometimes RBCs are present in conjunction with a high bacterial count.

 
Pap Smear
What it measures. The Pap smear makes it possible to take a microscopic look at the cells around the outside and inside of the cervix. Disorders of the cervix might cause no symptoms?and without this test, might not be caught.
What it tells you. Upon close examination, this test can assess whether the cells look normal. There are many possible causes of abnormal cells, including mild inflammation caused by a vaginal infection such as yeast, a viral infection from human papilloma virus (the virus that causes genital warts), and cancer. Depending on the severity of the findings, follow-up Pap smears or a procedure called a colposcopy, which allows for a microscopic look at the cervix, might be needed.

 
Gonorrhea and Chlamydia
What it measures. This test can be done at the same time as the Pap smear by taking a swab from the cervix and getting a bacterial culture. It can also be tested in a special urine test called a polymerase chain reaction (PCR) test, which is more accurate than a culture. In either, the tests will show the presence of the bacteria that causes these infections. Both infections can possibly go undetected due to lack of symptoms in the mother, and both have serious consequences for the infant, the mother, and the partner if untreated.

What it tells you. This test can tell you if you have the infection, but it cannot tell you when or from whom you received it. This is especially true with chlamydia, often called the silent infection. The results are only as good as the performance of the test and the ability to swab the areas affected. False-negatives can occur where the infection is present, but not detected. False-positives are rare. Pregnant women who are positive will be treated and then re-tested to confirm that any infections are gone.

Other Prenatal Tests:

Second Trimester Tests

Third Trimester Tests

Genetic Tests

Tests to Evaluate Baby

*taken from "On the Road to Motherhood," by Mayri Sagady Leslie, CNM, Every Baby magazine, Issue Four.