Pregnancy Third Trimester (28 weeks to delivery)

Third Trimester Pregnancy Lab Tests and health information

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For women who engage in high-risk activities, such as intravenous drug use or unprotected sexual contact that can contribute to HIV or hepatitis B infection, it is highly advised that these women test for these infections during the third trimester of their pregnancies. Further, it is highly recommended (in fact, required in some states) to test or repeat the tests for sexually transmitted diseases such as syphilis, gonorrhea, and chlamydia in the third trimester. 

A non-stress test (NST) may also be given to pregnant women. This is a non-invasive test performed after the 28th week to monitor health and look for indications of distress in high-risk pregnancies or babies past due. The test also measures the fetal heart rate concerning movement.  

When healthcare practitioners are concerned about how contractions affect fetal heart rate, what is known as a contraction stress test may be performed following the stress test. The process involves medication given to the woman to induce mild contractions (stress). Then, the heart rate of the fetus is monitored.  

Urine Screen for Glucose or Protein 

The expectant mother may be asked to provide a urine specimen at each prenatal visit throughout the first, second and third trimesters. Urine testing is typically conducted in the office using a dipstick when screening for glucose (sugar) or protein. Small levels of protein and glucose are normal in urine. However, high levels can represent a problem and may require further testing.  


High levels of protein in urine could mean that there is kidney damage or disease. It could also mean that there is a transient elevation. This could be due to: 

  • Infection 
  • Emotional stress 
  • Physical stress 
  • Medication 

The additional tests needed to determine the cause include a complete urinalysisa 24-hour urine protein test, and urine culture (to identify any present yeast present or any bacteria).  

During the second and third trimesters, one particularly concerning condition, is preeclampsia (also known as toxemia or pregnancy-induced hypertension), which involves high blood pressure and excessive amounts of protein in the urine. It occurs in about eight percent of all pregnancies, and the symptoms include: 

  • Weight gain 
  • Swelling 
  • Vision changes 
  • Headaches  

The risk factors for preeclampsia include:

  • Pregnancy 
  •  Being pregnant with more than one child 
  • Women over the age of 40 
  • Teenagers 
  • African Americans 
  • Having diabetes 
  • Having kidney disease 
  • Having hypertension 

Preeclampsia can reduce air and nutrition getting to the infant through the placenta, which causes low birth weight or other serious issues. However, if preeclampsia is caught early enough by regularly checking urine protein levels and blood pressure, serious health problems can be managed for both the mother and the baby. 


A sign of undiagnosed diabetes existing in a mother could be high urine glucose levels. Gestational diabetes, which is a type of diabetes that can occur during pregnancy, is another sign. After a positive urine test for glucose, a confirmatory blood glucose test is typically conducted. A confirmatory blood glucose test is also routinely used to screen during the second trimester (24 to 28 weeks of pregnancy) for gestational diabetes.  

A Urine Culture, Used to Decide Bacteria in the Urine (First-time or Repeated.) 

Many organizations recommend pregnant women get screened for asymptomatic bacteriuria using a urine culture between 12 to 16 weeks gestation or at the first prenatal visit. These organizations include: 

  • The American College of Obstetricians and Gynecologists (ACOG) 
  • The United States Preventative Services Task Force (USPSTF) 
  • The Infectious Diseases Society of America (IDSA) 
  • The American Academy of Family Physicians (AAFP) 

It should be noted that the ACOG recommends the screening at the first prenatal visit and then repeated in the third trimester if you are relying on information from this specific organization. 

When large amounts of bacteria are found in a urine culture during pregnancy, it's known as asymptomatic bacteriuria. A woman with this condition will not experience any associated urinary tract infection, such as pain or urgency to urinate. Approximately 2 to 10 percent of American pregnant women have this condition. Asymptomatic bacteriuria can lead to severe kidney infections and increase the risk of low birth weight and preterm delivery. It is advised that women suffering from asymptomatic bacteriuria seek appropriate antibiotic treatment. 

Group B Strep Screen  

Group B streptococcus (GBS) is a common bacteria present as a part of the normal vagina flora and gastrointestinal areas of about 25 percent of women. Group B streptococcus (GBS) is not like Group A streptococcus, which causes strep throat.  

Group B streptococcus is not usually a problem unless it is present in the vagina during delivery. If the bacteria is present during delivery, the infection can spread to: 

  • · The uterus 
  • · The urinary tract 
  • · The amniotic fluid 
  • · The incision made during a cesarean 

As the baby passes through the mother's birth canal during delivery, the baby can inhale or ingest the group B strep bacteria.  

Within six hours of birth or as late as two months of age, the infant will display symptoms if an infant is infected. If left untreated, an infant can:

  • · Become septic 
  • · Develop pneumonia 
  • · Develop physician disabilities 
  • · Develop learning disabilities 
  • · Suffer hearing and vision loss 

To determine the risk of a pregnant woman infecting her infant at delivery, the U.S. Centers for Disease Control and Prevention (CDC) recommends screening pregnant women for GBS between 35 to 37 weeks of gestation. To determine if Group B strep bacteria are present, within 24 to 48 hours, samples of the mother's vaginal and rectal areas are collected. If it is found that the bacteria is present, or if the mother goes into labor before testing is complete, it is recommended that the mother get antibiotics intravenously during her delivery.  

Throughout a woman's pregnancy, GBS bacteria can come and go. Therefore, it is not helpful to test for GBS early in the pregnancy. Testing at that time will not determine if it is present during labor or if it could spread to the baby during delivery. Testing late in the pregnancy (35 to 37 weeks) is what is useful for accuracy—also, treating with oral antibiotics before labor is not proven to stop GBS infections in newborns.  

Complete Blood Count (First-time or Repeated) 

complete blood count (CBC) tests the cells circulating in the blood. There are three kinds of cells suspended in plasma that blood consists of white blood cells (WBCs), red blood cells (RBCs), and platelets (PLTs). A CBC can be done before pregnancy, in the beginning, or one or more times during pregnancy to identify and stop problems. After baseline values are established from initial testing, results from follow-up testing can be compared to them to check for any changes that could indicate a health issue.  

Red Blood Cells 

When a woman is pregnant, her hemoglobin must be able to supply enough oxygen to both her and her fetus. Hemoglobin is the oxygen-carrying protein found in red blood cells. Hemoglobin binds to oxygen in the lungs, spreads it throughout the body, and gives it to cells and tissues. A woman with insufficient red blood cells or hemoglobin is anemic.  

Lots of pregnant women will have some degree of anemia. Mild anemia can cause tiredness and weakness. But severe anemia in a pregnant woman can cause the fetus not to receive enough oxygen for normal development.  

During delivery, every woman loses a small amount of blood. This is typically not a problem, but even small amounts of blood loss can be dangerous to an anemic woman. Therefore, healthcare practitioners might want to determine the hemoglobin level in a pregnant woman's blood before delivering, which will assess the possible impact of the expected blood loss.  

White blood cells 

The purpose of white blood cells is to protect the body from infection and serve other immune functions. When a woman's white blood cells are involuted during pregnancy, it can help determine infections to treat and resolve before significant health problems occur for the mother or her baby.  


Special cell fragments in the blood are called platelets. They help to form clots to stop bleeding. Women who have low platelet counts or improperly functioning platelets are at risk of life-threatening bleeding during delivery. If a platelet count problem is identified, follow-up testing may be needed to create treatment options. 

Thyroid Stimulating Hormone if a Female Has Thyroid Disease History 

When a woman is pregnant, regular changes occur in the functioning of the many endocrine glands. However, it has a definite effect on the thyroid gland. The thyroid gland produces hormones, such as triiodothyronine (T3) and thyroxine (T4), essential to the mother's health and healthy fetus development.

If a female has thyroid conditions, she requires careful monitoring if she becomes pregnant. A healthcare practitioner may conduct tests for thyroid-stimulating hormone (TSH) to monitor a woman's thyroid function throughout her pregnancy. The pituitary, a small gland in the brain, creates TSH and responds to low T3 or T4 levels. If a woman is taking thyroid hormone replacement medication but still shows increased TSH levels, it may mean that the dose needs to be increased.  

It is advisable to screen women before pregnancy or during the first trimester for elevated TSH, even if there is no history of thyroid disease. A large percentage of women may have an underlying thyroid disorder that can cause issues during pregnancy. 

RBC Antibody Screen  

There are several blood types: 

  • AB 

Each blood type can also be Rh positive or negative. 

Every pregnant woman should know her blood type. [See Blood Typing for more information.] Both mother and child may experience problems if their blood types are not the same or if the mother is Rh-negative and the fetus is Rh-positive, resulting in a severe condition known as Hemolytic Disease of the Newborn (HDN). 

 The woman's immune system can create an Rh antibody that attaches to the Rh-positive antigens on her baby's red blood cells and sets them up for destruction. The first Rh-positive baby is not likely to become ill. However, the antibodies produced will affect future Rh-positive babies.  

An Rh-negative mother is less likely to develop this antibody if given the routine Rh immune globulin injection (rhogam) at about 28 weeks gestation. In addition, injections could be necessary during her pregnancy if she has chorionic villus sampling, amniocentesis, or an abdominal injury. Also, injections could be required after delivery if the baby is Rh-positive. Before a woman receives an injection, a screen for antibodies is done to ensure Rh antibodies are not already present. 

In addition, women who have had blood transfusions or had prior pregnancies could create an antibody to blood factors other than Rh that has the potential of harming an unborn baby. Getting an antibody screen during a woman's first trimester can determine if potentially harmful antibodies are present in the mother's blood. When a harmful antibody is present, if possible, the baby's father should be tested. This will determine if the father's blood has antigens that react with the mother's antibody. If there's a reaction, the fetus may also have the same antigens as the father. If the antibody reacts with the fetus', a healthcare practitioner should evaluate the mother's antibody level and the fetus for the length of the pregnancy. If there are signs that the fetus is becoming ill, it could mean that treatment before birth (such as intrauterine transfusion) or early delivery is required.  

Rh incompatibility has serious consequences. One of the most common causes of HDN is the incompatibility between the baby's ABO blood groups and the mother's. Therefore, you can't use the RBC antibody screen to see if HDN will occur because antibodies to the ABO blood groupings occur naturally. 

Fetal Fibronectin (fFn) for a Woman With Preterm Labor  

This test is given if a woman is between 22 to 25 weeks pregnant with premature labor symptoms to determine premature delivery risks. What is desired is an intervention to protect the preterm baby. 

Vaginal fluid or a cervical sample is collected and analyzed for fFN, a glycoprotein located between the lining of the uterus and the amniotic sac. There can be high levels because of other causes other than the risk of preterm delivery. Thus, a positive fFn result is not entirely reliable for preterm labor and delivery. Nevertheless, a negative fFN is highly determinative that preterm delivery won't occur within 7 to 14 days. Risks are present when treating a woman for premature labor. A negative fFn can eliminate unnecessary hospitalizations and drug therapies.  

Amniocentesis if Risk of Preterm Labor  


While the procedure is conducted, a medical professional inserts a needle through the walls of the abdomen, uterus, and the thin-walled fluid sac surrounding the developing fetus. Amniotic fluid is withdrawn in a small amount. Inside the fluid is AFP created by the baby and fetal cells. A medical professional can test these fetal cells for genetic or chromosomal abnormalities. Based on family history, a gene analysis may be performed to check for the possibility of the child being born with a birth defect or hemoglobinopathy. Or research on the results of screening tests done on the parents (for cystic fibrosis, for example.). To complete the testing, approximately two weeks are needed.  

A slight risk exists with amniocentesis in this situation. The needle inserted into the amniotic sac could puncture the baby, which would cause a small amount of amniotic fluid leakage, an infection, or in rare situations, even a miscarriage could result in the pregnancy. 


Pre-eclampsia is among the more severe conditions that can impact women who are pregnant. This condition is diagnosed when a pregnant woman displays three different factors. The first is hypertension or high blood pressure. The second is proteinuria or protein in the urine output, and the third is swelling of her feet, hand, and/or face. In the most serious cases, there might even be evidence of liver and kidney damage, fluid accumulation in the lungs, and central nervous system disturbances. Pre-eclampsia rates among pregnant women range from 3 up to 7 percent, and it typically happens after week 20 of the pregnancy. 

Untreated pre-eclampsia can be very risky since it might hurt the physical organs of the mother’s body and also result in seizures. These seizures are known as eclampsia. If not treated immediately, they are typically fatal for both the mother and child. Both pre-eclampsia and eclampsia can result in premature delivery and low baby birth weight, either of which can result in health issues for the child. Also, placental abruption is another possibility, and this is where the placenta gets loose from its uterus prior to the birth of the baby, resulting in bleeding. 

Pre-eclampsia might also develop into HELLP syndrome, which is another condition that is life-threatening. It’s known as HELLP given how it’s defined by a breakdown in red blood cells, known as Hemolysis, along with Elevated Liver enzymes, as well as a Low Platelet count. 

One in  200 females that have untreated pre-eclampsia wind up progressing to full eclampsia. The majority of eclampsia cases happen in either the third trimester of the pregnancy or in the 4 days following the delivery of the child. In rare cases, it can develop as much as 6 weeks following delivery. 

Pre-eclampsia can result in symptoms very similar to what happens in a normal pregnancy. Also troubling is the fact that some women who have pre-eclampsia demonstrate no symptoms whatsoever. Thus, it’s crucial for pregnant women to attend all their routine prenatal checkups. In these checkups, healthcare professionals do both physical exams and laboratory tests where they look for the ‘quiet’ signs of the condition, including protein output in the urine stream and high blood pressure. 

Currently Known Risk Factors 

Medical and scientific researchers are still attempting to ascertain the specific reasons why pre-eclampsia happens. On the other hand, there are certain risk factors that are already known.

They include but are not always limited to the following: 

  • Any prior pregnancies involving pre-eclampsia 
  • Any family history of there being pre-eclampsia 
  • First-time pregnancy 
  • Pregnancy past the age of 35 
  • Overweight to the point of obesity 
  • Carrying more than one baby 
  • Personal history of other conditions, which include migraine headaches, chronic hypertension, both type 1 and 2 diabetes, lupus, antiphospholipid syndrome, kidney disease, and/or a hypercoagulable state meaning higher tendencies for blood clots 


Pre-eclampsia can be a very serious complication for a pregnant woman, and there might not be any obvious symptoms to it. When symptoms are present, it can seem as if they’re just typical pregnancy symptoms. For instance, swelling and weight gain can both indicate pre-eclampsia, and yet they’re also present during otherwise normal pregnancies too. Hypertension is another warning sign of pre-eclampsia, which often goes unnoticed up to the point it’s detected by healthcare practitioners during regular prenatal visits. 

If you have any of the symptoms or signs related to pre-eclampsia, or you notice any sudden changes during your pregnancy, then it’s crucial that you inform your healthcare provider immediately. They will then look for any other signs of this condition and also help monitor all your symptoms. Pre-eclampsia that goes untreated can be a very serious condition that can even prove fatal for both you and your child. Make sure you get to all your prenatal checkups, and also seek medical attention if and when symptoms arise. 

Pre-eclampsia symptoms might include the following: 

  • Sudden gains in weight of more than 2 pounds per week 
  • Edema, a sudden swelling of the face and hands 
  • Headaches of a persistent nature 
  • Changes in vision, including sensitivity to light, temporary loss of vision, blurry vision, and sensations of flashing light 
  • Bluish skin due to poor circulation 
  • Vomiting or nausea, particularly if it happens suddenly past mid-pregnancy 
  • Reduced output of urine 
  • Shortness of breath due to higher blood pressure or fluid buildup in the lungs 
  • Shoulder or stomach pain and pinching, particularly along the upper right side of the abdomen or if laying down on your right side, as these might demonstrate liver problems 

Some pre-eclampsia signs can be detected during physical examination. Should you experience any of these, seek out medical care immediately. 

They include the following: 

  • Elevated blood pressure 
  • Atypically strong leg reflexes, like when your healthcare practitioner uses a rubber hammer to tap your knee 
  • Shortness of breath, abdominal pain, severe headaches, and blurred vision are all very serious pre-eclampsia symptoms


When left untreated, the condition of pre-eclampsia can result in very serious and even potentially life-threatening complications for both mother and child. 

Potential complications include the following: 

  • Eclampsia/seizure 
  • Rupture of the liver 
  • Stroke 
  • Low baby birth weight 
  • Placental abruption where the placenta gets loose from its uterus prior to the delivery of the baby, resulting in bleeding 
  • Women that have a personal history of pre-eclampsia have higher odds of developing: 
  • Cardiovascular disease 
  • Diabetes 
  • Kidney disease 

Testing Related to Pre-Eclampsia 

At the time of this writing, there’s not a single test for reliably identifying pre-eclampsia during early pregnancy. As such, the ACOG, or American College of Obstetricians and Gynecologists, suggests that, instead, healthcare practitioners conduct pre-eclampsia screening during the first trimester by getting a thorough medical history of women, and assessing for known risk factors. 

During a regular prenatal exam, healthcare practitioners lookout for symptoms and signs of pre-eclampsia, including atypical weight gain, swelling of the face and hands, and high blood pressure. During the 2nd and 3rd trimesters, there are urine tests for high volumes of protein, which can be a potential warning sign of pre-eclampsia. 

If you have any symptoms or signs of pre-eclampsia, then your healthcare provider is likely to conduct additional imaging and laboratory tests in an attempt to first diagnose the condition and secondly ascertain its level of severity. 

Laboratory Testing 

Proteinuria, or protein in urine output, was once thought of as a pre-eclampsia diagnostic sign. On the other hand, not every woman with the condition of pre-eclampsia actually has proteinuria. ACOG doesn’t recognize proteinuria as a required sign of pre-eclampsia diagnosis any longer. These days, healthcare practitioners also look for high blood pressure on top of proteinuria. They might also look for high blood pressure and one of many other symptoms or signs, including edema, serious vision changes, poor function in the liver or kidneys, and/or low platelet count. 

The following tests are useful in the diagnosis of the condition, ascertaining its severity, and keeping up with its progression: 

Urine protein to creatinine ratio and urine protein tests are used to detect elevated levels of protein in urine output. 

Uric acidserum creatinine, and BUN tests all measure and analyze kidney functions to find pre-eclampsia organ damage and frequent measurements to monitor the condition. 

AST (or aspartate aminotransferase) and ALT (or serum alanine aminotransferase) are both liver function tests which look for elevated levels to indicate pre-eclampsia organ damage. 

CBC (or complete blood count) testing is ordered for detecting bloodstream changes like low platelet counts. 

PTT (or partial thromboplastin time) testing measures how long it takes for blood to clot, as pre-eclampsia might extend times for blood clotting. 

Antiphospholipid antibodies are looked for since this autoimmune disorder is a syndrome associated with a condition of pre-eclampsia, as well as other complications in pregnancy. Testing for such antibodies can ascertain if some autoimmune disorders might by underlying pre-eclampsia. 

HELLP syndrome can be a life-threatening variation of the condition of pre-eclampsia, as outlined earlier in this content. Should your healthcare provider suspect that you are afflicted with HELLP syndrome, then certain tests might happen, including: 

Total bilirubin, because elevated levels of this often indicate either red blood cell hemolysis or liver damage. 

Serum lactate dehydrogenase (or LD) testing looks for elevated LD levels that suggest cell or tissue damage, like the kind that happens when red blood cells breakdown.