By Cat Troiano
Pregnancy is an exciting time for moms-to-be as they anticipate the birth of their baby, and they rely on their physicians for guidance through each trimester. In addition to proper nutrition, stress reduction, plenty of sleep and safe activity levels, periodic checkups are essential in achieving the healthiest possible status for both the mother and for her developing fetus. Prenatal laboratory tests are an important part of these appointments so that any potential health issues can be addressed to ensure a safe pregnancy and uncomplicated delivery.
Types of Prenatal Tests
From pregnancy confirmation through delivery, expectant mothers undergo various laboratory tests to monitor their health as their bodies undergo hormonal shifts and metabolic changes to accommodate the growth and development of their fetuses. The types of prenatal tests that may be ordered include:
• Routine tests
• Selective tests
• Genetic tests
While some tests are ordered for every woman who is pregnant, others are only performed under certain conditions.
Confirming Pregnancy
Human chorionic gonadotropin (hCG) is a hormone that is produced by the cells of the placenta once conception takes place, and the level continues to increase every two to three days during the first 8 to 11 weeks of pregnancy.
A qualitative hCG test evaluates the presence of hCG in a blood or urine sample to confirm a patient’s pregnancy status:
• An hCG level that is lower than 5 mIU/ml is a negative result for pregnancy.
• An hCG level that is between 6 and 24 mIU/ml is inconclusive, and the test will need to be repeated to determine if the level increases.
• An hCG level that exceeds 25 mIU/ml is a positive result for pregnancy.
A quantitative hCG test is performed on a blood sample for monitoring purposes to ensure that the level of hCG is increasing appropriately during the first trimester. A low hCG level is not always indicative of a problem, and plenty of women with low hCG levels have given birth perfectly healthy babies. However, if the level does not increase, problems such as etopic pregnancy and miscarriage must be ruled out. Conversely, a higher than normal hCG level must also be investigated to rule out possible causes, such as a multiple pregnancy.
Routine Tests for All
Once the qualitative hCG test confirms a patient’s pregnancy status, routine laboratory screening tests are ordered for all expectant women.
A complete blood count (CBC) is performed during the first and third trimesters. This blood test, which evaluates the red blood cells, hemoglobin, white blood cells and platelets, enables the detection of the following conditions:
• Anemia, which can occur during pregnancy when the mother isn’t taking in adequate amounts of iron, folate or vitamin B12, posing the risk of delivering a premature or low birth-weight baby
• Infections, which can be passed along to the fetus
• Gestational thrombocytopenia, which is a condition that can develop during mid-to-late pregnancy and results in a low platelet count, reducing the blood’s ability to clot and increasing the risk of hemorrhaging
A urinalysis is performed at each prenatal appointment throughout the pregnancy. This urine screening enables the detection of these conditions:
• Gestational diabetes, which is a form of diabetes that can develop during pregnancy if hormonal changes result in high glucose levels and ketones in the urine
• Preeclampsia, which is a potentially fatal condition that can arise during pregnancy and is characterized by high blood pressure and high protein levels in the urine, putting the mother at risk for seizures, stroke, heart failure or coma and putting the fetus at risk for being stillborn
A urine bacterial culture may also be performed to detect bladder and urinary tract infections.
Blood typing and antibody screening is performed during the first trimester and repeated during the 28th or 29th week of pregnancy to verify that the mother’s and fetus’ blood types are compatible and that there are no Rh factor antibodies present.
A group B streptococcus (GBS) bacteria culture is performed during the 35th to 37th week of pregnancy. A baby can contract GBS during birth, which can result in the newborn developing meningitis or pneumonia.
If any abnormalities are discovered in these test results, additional tests may be ordered. Diligent monitoring, combined with appropriate treatment, is imperative in managing the condition. For example, if the CBC results show a hemoglobin count that is lower than the normal range of 12 to 15.5 grams per deciliter, additional tests, such as the ferritin serum test or the serum folate test, can determine if the anemic state is the result of an iron or folate deficiency, respectively. Once a deficiency is confirmed, appropriate supplementation can then be prescribed to correct the deficiency.
Other tests that are recommended by the American College of Obstetrics and Gynecology for all expectant mothers include screenings for the following diseases, which can result in complications or be passed to the fetus:
• Human immunodeficiency virus
• Human papilloma virus
• Rubella, or German measles immunity
• Varicella zoster virus (chicken pox) immunity
• Hepatitis B
• Chlamydia
• Syphilis
Mothers who have histories of certain medical conditions or who carry other risk factors may need to undergo additional tests.
Selective Tests for Mothers at Risk
Just as an expectant mother who has been managing hypertension should expect diligent blood pressure monitoring throughout her pregnancy to avert the development of preeclampsia, mothers with other health conditions must be equally diligent in staying on top of their health status. Some examples of laboratory screenings that are ordered in such cases include:
• The glucose challenge and/or glucose tolerance test, for those with pre-existing diabetes, those who have a prior history of gestational diabetes or those whose urinalysis results include elevated glucose levels and ketones
• TSH, for those with a history of a thyroid condition, such as hypothyroidism
• Zika virus test, for expectant mothers who have recently traveled to areas where this mosquito-borne illness is prevalent
• Tuberculosis test, for those who are HIV positive or who reside with someone who has tuberculosis
To minimize the chances of complications during pregnancy, labor and delivery, attentive monitoring and testing are recommended for all expectant mothers who carry higher risks. Some of these risks include:
• Obesity
• Pregnancy that was achieved with the help of fertility drugs
• Pre-existing conditions, such as hypertension, diabetes, thyroid disease, autoimmune disorders, HIV and kidney disease
• Pregnancy during the teen and over-35 age groups
• Lifestyle habits, including smoking, alcohol consumption and illicit drug use
In addition to patient risk factor assessment, an important part of the patient history chart is the notation of all known family medical history, including the existence of hereditary conditions.
Genetic Tests
Genetic tests can determine whether or not the fetus has a particular hereditary disease that was carried by either parent. Genetic tests can be performed on the mother or father prior to conception if there is a family history of the disease to confirm whether or not she or he is a carrier of the disease or actually has the illness. Some examples of hereditary diseases include:
• Sickle cell anemia
• Alpha thalassemia
• Beta thalassemia
• Hemophilia A
• Cystic fibrosis
• Down syndrome
• Muscular dystrophy
• Polycystic kidney disease
• Huntington’s disease
The fetus can also be tested for genetic diseases and defects. The prospective parents should discuss the options with the physician and weigh the risks and benefits of fetal testing procedures. Throughout the pregnancy, sonogram imaging will be performed to monitor the growth and development of the fetus and to detect physical abnormalities.
Once a pregnancy is confirmed, performing all routine tests as well as selective tests when appropriate will enable early detection of any metabolic changes or other medical conditions that arise so that safe treatment plans can be implemented to manage the condition. This aspect of prenatal care is valuable in maximizing the expectant mother’s chance of safely carrying her baby to term, experiencing a delivery that is free of complications and welcoming a healthy new bundle of joy.
Thank you to www.niddk.nih.gov for the image