What Is Prenatal Testing?
Prenatal testing is the tests offered to women during their pregnancy to detect whether the developing fetus has a genetic condition or congenital disability possibility. Performing prenatal testing is useful in determining different approaches for the pregnancy or specific management during the pregnancy and delivery for improvement in the outlook for the baby. Several types of prenatal testing are available, depending on the trimester of the pregnancy and the type of condition in focus. This article overviews various prenatal tests for pregnant women in their third trimester.
What Is the Difference Between Screening and a Test?
It is important to understand the purpose of screening tests. Knowing the difference between a diagnostic test and screening is also important. A confirmatory diagnostic test must follow a positive screen before the doctor makes significant irreversible decisions. Likewise, it is also important to understand that a negative result on a screening test is not a guarantee of no issues.
What Are the Different Tests and Screenings Done in the Third Trimester?
The purpose of third-trimester prenatal testing, in general, focuses on the well-being of the mother and reducing fetal morbidity and mortality. Various tests that the doctor may perform during the third trimester are as follows:
Ultrasonography:
1. The doctor will perform an abdominal ultrasound during the third trimester and before delivery to assess the fetal position and to estimate and monitor the weight of the fetus. The doctor will document the weight and position of the fetus during the third trimester.
2. During the late phase of the third trimester, the fetus will shift into the position for birth. This will involve flipping over so that the head of the fetus is down in your uterus. Then, the fetus will start moving down in the uterus towards the birth canal, which is a cervix just below the uterus and connects to the vaginal opening.
3. However, in some cases, the fetus does not get into this ideal head-down position before birth. There are several other positions that the fetus can be in, and these positions may cause some complications during childbirth. Hence it is essential to do an ultrasound screening during the late third trimester of the pregnancy. These deviations in fetal positions can include the following:
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Occiput or Cephalic Posterior Position: in this position, the head of the fetus is facing the abdomen of the mother and not upside down. The fetus looks at the ceiling with the fetal head in this position. This position is also known as sunny-side-up. This position during the labor can increase the chance of pain and duration of childbirth.
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Frank Breech: In this position, the buttocks of the baby are towards the way into the birth canal. Hips are flexed, and the knees are extended towards the mother's abdomen. This position has an increased risk of forming an umbilical cord loop which can precede the fetal head through the cervix. It may cause injury to the baby during vaginal delivery.
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Complete Breech: In this position, the fetus is first positioned with the buttocks towards the birth canal, with the hips and knees folded under themselves. Like the frank breech position, this presentation also increases the chances of forming an umbilical cord loop which could precede the fetal head through the birth canal and injure the baby in case of vaginal delivery.
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Transverse Lie: In this position, the fetus lies crosswise in the womb, making it more likely that the shoulder of the fetus will enter the birth canal first. The doctor will suggest a cesarean (C-section) for most fetuses in this position at delivery.
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Footling Breech: In this position, one or both the feet of the baby are pointed down toward the cervix. This increases the risk of the umbilical cord looping, which may cut off the blood supply to the fetus.
Streptococcus Agalactiae (Group B Streptococci Beta-Hemolytic):
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It is one of the major causes of morbidity and mortality in unborn and newborn fetuses. Therefore, the doctor may prescribe vaginal screening for group B streptococci beta-hemolytic, typically in the late third trimester, the 34 to 37 weeks of conception.
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If positive bacterial culture is found, the doctor can provide effective treatment to the affected mother during labor before the initiation of the delivery.
Repeat Tests:
Many doctors also advise repeat evaluations of the following tests:
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Hemoglobin and Hematocrit Value: The disease control and prevention center has suggested hemoglobin levels below 11 grams per deciliter (g/dl); a hematocrit value less than 33 percent in the third trimester is considered anemia. Many studies have established that maternal anemia in the third-trimester lead to prolonged hospitalization time after the child birth. Anemia affects the fetus in the prenatal and postpartum periods
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Syphilis Serology: The center for disease control and prevention has advised serologic testing for syphilis twice during the third trimester that is at around 28 weeks of gestation and at the time of delivery, for pregnant women living in communities with a high rate of syphilis and for pregnant women who has a history of being at risk for syphilis infection during pregnancy.
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HIV (Human Immunodeficiency Virus) Screening: The American college of Obstetricians and gynecologists recommends repeat testing of HIV in the third trimester, before 36 weeks of gestation, for pregnant women with negative HIV antibody tests done initially who are at high risk of getting HIV infection or who pose signs and symptoms that are consistent with acute HIV infection.
Other Tests:
At every prenatal visit during the third trimester, the doctor will perform the following tests to ensure the health of the mother and fetus:
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Maternal vital signs.
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Fetal heart rate.
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Uterine fundal height (vertical measurement of the distance from the top of the uterus to the pubic bone).
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Maternal weight.
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Urinalysis for glucose, protein, and leukocytes.
Conclusion:
During the third trimester most common complications can result in increased mortality and morbidity of the fetus. Hence it is as essential to undergo prenatal tests as the first and second trimesters. The doctor will advise and perform a test depending on the general condition of the pregnant woman and fetus and the prenatal test results of previously done tests.
