9.10 Third Trimester Prenatal Care

Interval History

The list of symptoms assessed are the same as the second semester visit, with the addition of fetal movement observations. By the third trimester, the pregnant client should be feeling the fetus move regularly. If a longer than normal period of time passes without the fetus moving, the provider may recommend the pregnant client count the fetus’s movements, known as kick counts. Read more about kick counts under the “Health Teaching During the Third Trimester” subsection. Additional diagnostic testing is performed if kick counts are abnormal.^[1]

Objective Data

Third trimester prenatal visits, similar to prenatal visits in the first and second trimesters, include assessing weight, blood pressure, fundal height, fetal heart rate, fetal movement, urine dipstick testing, and screening for pregnancy complications. If the pregnancy continues to be normal, follow-up visits are scheduled for every two weeks until 36 weeks of gestation and then weekly until delivery. At 36 weeks’ gestation, additional laboratory testing is performed and vaginal exams may begin.^[2]

After 36 weeks of gestation, the measurement of the fundal height in centimeters no longer approximates the number of weeks of gestation. At this point in the pregnancy, the fetus begins descending into the pelvis of the pregnant client in preparation for labor and birth.^[3]

At 32 weeks or more of gestation, the physical exam of the pregnant client by the health care provider includes Leopold’s maneuvers. Leopold’s maneuvers are a set of four steps (maneuvers) performed by the nurse when palpating the pregnant client’s abdomen. The four Leopold’s maneuvers are as follows:

• Palpate the sides of the pregnant client’s abdomen to determine the fetal lie (relationship of the fetal spine to the mother’s spine).
• Palpate the fetus to determine the location of the fetal back.
• Palpate the fundus and identify the fetal parts in the fundus.
• Palpate the suprapubic area to identify the fetal presentation (the fetal part present in the lower part of the uterus).

See Figure 9.23^[4] for an illustration of the four Leopold’s maneuvers or a video demonstration of performing Leopold’s maneuvers in the following box. In the illustration, the fetus has a longitudinal fetal lie that is in alignment with the maternal spine, and the fetal head is present in the lower part of the uterus.

Vaginal Exam

Starting at 36 weeks’ gestation or later, a vaginal exam is performed when indicated by the interval history or upon request by the pregnant client. Using a gloved hand, the health care provider places their lubricated index and adjacent finger gently into the client’s vagina. Using the two fingers, the health care provider locates the cervix and estimates its length and then inserts one or both fingers into the cervical os to determine if the cervix is opening. Next, the health care provider palpates and identifies the fetal presenting part and determines how far down inside the pelvis the presenting part has descended. Another purpose of the vaginal exam is to determine if the cervix is ripening. The softening and opening of the cervix as it prepares for labor is called cervical ripening, and it may occur as early as 37 weeks for multiparas and is more likely to occur at 39 weeks or later for primiparas.

Routine Laboratory Testing

Laboratory testing during the third trimester occurs at 36 weeks of gestation. This testing includes a CBC or hemoglobin/hematocrit, syphilis test, vaginal and rectal swab check for group B beta-hemolytic streptococcus (GBS), and cervical cultures for chlamydia and gonorrhea. The testing is performed at 35 to 37 6/7 weeks; therefore, the results are available before the client goes into labor and are valid for up to five weeks. If testing is positive for STI, the client is treated before labor and birth to decrease the chance of transmitting the infection to the newborn.

Group B beta-hemolytic streptococcus is one of the leading causes of newborn infection. Twenty-five percent of pregnant clients are carriers of GBS. The vaginal and rectal swab for GBS is performed to identify carriers of GBS. If the GBS culture is positive, the pregnant client is provided the results, and treatment with antibiotics is recommended during the labor process. Treatment is delayed until labor because the GBS bacteria can recolonize the vagina before the birth when treated antepartum.

Additional Diagnostic Testing

Several diagnostic tests may be ordered by the health care provider to assess fetal well-being when kick counts are abnormal or other nonreassuring symptoms occur, including a fetal nonstress test (NST) or biophysical profile (BPP). A contraction stress test may be recommended if the NST is nonreactive or unclear.^[6]

Fetal Nonstress Test

A fetal nonstress test (NST) is a noninvasive test to assess fetal well-being. It provides a graphic of the fetal heart pattern in relation to fetal movements and can be performed starting at 28 weeks’ gestation. The test is termed “nonstress” because it only consists of monitoring. An external fetal monitor and uterine contraction monitor is placed on the mother’s abdomen to measure fetal heart rate and movement. If the fetal heart rate increases by at least 15 bpm above the baseline for 15 seconds for a fetus at 32 weeks or greater, or 10 bpm for 10 seconds in the fetus less than 32 weeks, two or more times during a 20-minute testing period, it is considered a reactive NST and is considered a reassuring result. If there are insufficient accelerations of the fetal heart rate within the 20- to 40-minute window or the accelerations do not meet the required criteria, the NST is interpreted as “nonreactive.” However, a nonreactive result does not necessarily indicate a health problem. The fetus may have been sleeping and not easily awakened. Certain medications taken during pregnancy may also cause a nonreactive result. The health care provider will review the results and determine if additional testing is needed to find out if there is a cause for concern. See Figure 9.24^[7] for an image of a reactive nonstress test result. In this illustration, the FHR increased at least 15 beats per minute (bpm) above the baseline of 130 two or more times in this 10-minute tracing, resulting in this being interpreted as a “reactive nonstress test.”

When the fetal heart rate increases in association with fetal movement, this indicates adequate oxygenation, a healthy neural pathway from the fetal central nervous system to the fetal heart, and the ability of the fetal heart to respond to stimuli. FHR accelerations without fetal movement are also considered a reassuring sign of adequate fetal oxygenation. If the fetal heart rate does not accelerate with movement, the fetus can be sleeping. If a sugary snack is provided to the mother and there are still no movements after 40 minutes, vibroacoustic stimulation (VAS) may be performed. During this test, the vibroacoustic stimulator is placed on the pregnant client’s abdomen near the location of the fetal head. The stimulator produces a sound at a predetermined level for one to three seconds. The expected response by the fetus is the startle reflex, causing an acceleration of the fetal heart rate. The acceleration is linked with fetal well-being. The absence of the startle reflex in the fetus is nonreassuring and requires further testing, such as a biophysical profile or contraction stress test to evaluate the metabolic condition of the fetus. After 40 minutes, if the test remains nonreactive despite these actions, the nurse notifies the health care provider and anticipates further testing, such as a biophysical profile.

The nurse can help prepare the pregnant client for this test by explaining why the test is recommended and what happens during the test. The test is termed “nonstress” because it only consists of monitoring and the fetus is not “stressed” by stimulated uterine contractions. The test may be done in the provider’s office or at the hospital. The nurse will attach two devices around the pregnant client’s abdomen. One device will measure the fetal heart rate, and the other will record the pregnant client’s uterine activity. The pregnant client will be instructed to press a button on a cable attached to the fetal monitor each time they feel the fetus move. If the test is reactive, the nurse will inform the health care provider and provide the pregnant client with further education and instructions as prescribed.

Biophysical Profile

A biophysical profile may be performed if other prenatal screenings came back nonreassuring, such as a nonreactive stress test or maternal reports of decreased fetal movement. Predicting the condition of the fetus is more accurate if several parameters are evaluated. A biophysical profile (BPP) assesses five parameters of fetal well-being:

• Fetal heart rate pattern per NST
• Fetal breathing movements
• Fetal body movements
• Fetal muscle tone
• Amount of amniotic fluid

Normal values for each parameter suggest adequate neurologic function and oxygenation. Each of the five areas is given a score of zero or two for 10 total possible points. See Table 9.10a for BPP scoring.

Table 9.10a. Biophysical Profile Scoring^[8]

A BPP is an indicator of fetal well-being, and a score of 8 or 10 is considered normal and indicates a decreased risk of fetal asphyxia within one week. A score of 6 is considered abnormal and should be repeated within 24 hours. A score of 2 or 4 is not reassuring, and the provider may recommend inducing labor or scheduling a cesarean delivery for the pregnant client. A score of zero indicates impending fetal asphyxia, and an emergent cesarean delivery at a hospital with a neonatal intensive care unit is recommended.^[9]

The nurse’s role involves educating the pregnant client about the BPP. The nurse can help prepare the pregnant client by explaining why the test is recommended and what to expect during the screening.

Amniotic Fluid Index (AFI)

The amniotic fluid index (AFI) is a standardized way to assess the sufficiency of the amniotic fluid quantity in pregnancy and is obtained via ultrasound. This test can be done on pregnant clients who are at 24 weeks’ gestation or greater with a singleton pregnancy. This test is also part of the biophysical profile and is an indicator of fetal well-being. A normal AFI is 5 cm to 25 cm. A normal pocket of amniotic fluid is greater than 2 cm.^[10]

An AFI test may be recommended if there are concerns of polyhydramnios (too much amniotic fluid) or oligohydramnios (not enough amniotic fluid). Oligohydramnios can occur if the pregnant client’s amniotic membrane has ruptured and amniotic fluid is leaking. It can also occur due to kidney problems in the fetus. If the fetus receives inadequate nutrients and oxygen from the placenta, blood will be shunted away from the fetal kidneys. This decreases the glomerular filtration rate (GFR) and results in decreased urinary output. This causes a decrease in amniotic fluid due to the decreased urine production by the fetal kidneys. Persistently low levels of amniotic fluid may be associated with a birth defect of the fetus.^[11]

Polyhydramnios may have no definite cause. The normal fetus constantly swallows amniotic fluid and urinates to create more. If the fetus is not able to swallow normal amounts of amniotic fluid, it can lead to polyhydramnios. This could indicate gastrointestinal malformations, fetal neurologic problems, or mechanical obstruction of the esophagus. Increased amniotic fluid production can also result from polyuria, which can occur with uncontrolled maternal diabetes. This may be associated with fetal macrosomia.^[12]

Contraction Stress Test

A contraction stress test (CST) evaluates the response of the fetal heart rate to uterine contractions that are stimulated by the administration of oxytocin. If the fetal heart rate decreases after uterine contractions, this means the fetus is not receiving enough oxygen due to placental insufficiency or other factors. This test is no longer used very frequently because a BPP is less invasive.^[13]

During the CST test, an external fetal and contraction monitor is applied to the maternal abdomen, and an oxytocin intravenous infusion is administered to cause the uterus to contract. The expected uterine contraction pattern for a CST is at least three uterine contractions lasting a minimum of 40 seconds each within a 10-minute period.^[14]

The CST test results are interpreted using several categories^[15]

• Negative: This result means there are no late or variable decelerations in the fetal heart rate (FHR) associated with uterine contractions. See Figure 9.25^[16] for an example of a negative CST. In this illustration, the FHR is at the top of the strip and uterine contractions are on the bottom. This strip shows that with each contraction, the FHR does not decrease, which makes it a negative result.
• Positive: This result means the FHR decreases immediately after a uterine contraction, referred to as a late deceleration. Late decelerations indicate fetal hypoxia. See Figure 9.26^[17] for an example of a positive CST with a decreased FHR just after a uterine contraction.
• Equivocal-suspicious: This result means there are intermittent late decelerations or other significant variable decelerations in FHR.
• Equivocal: This means there are FHR decelerations present during uterine contractions that occur more frequently than every two minutes or last longer than 90 seconds.
• Unsatisfactory: The tracing shows fewer than three uterine contractions in ten minutes or is otherwise uninterpretable.

CST is performed to identify the fetal hypoxia so that appropriate medical interventions can be performed to prevent an adverse outcome, if possible. It can also identify normally oxygenated fetuses to allow pregnancy to continue safely and avoid unnecessary medical intervention.^[18]

The nurse can help prepare a pregnant client for a CST by explaining why the test is recommended, answering any questions, and describing what will happen during the test. Prior to the CST, the nurse will need to get a baseline tracing of the FHR, and the nurse will also monitor the FHR tracing afterwards while a plan of care is being determined by the health care provider.^[19]

Tests to Determine Fetal Lung Maturity

A test for fetal lung maturity is recommended when non-emergency delivery is being considered before 38 weeks of gestation to reduce the risk of respiratory distress in the newborn. The lecithin/sphingomyelin (L/S) ratio is the best-known test for estimating fetal lung maturity. Lecithin and sphingomyelin are lipoproteins that make up surfactant, which is present in the pulmonary alveoli of term infants. Surfactant keeps the alveoli open by reducing surface tension on their inner walls. The decreased surface tension prevents collapse of the alveoli when the infant exhales, reducing the effort of breathing.^[20]

Health Teaching During Third Trimester

Kick Counts

Fetal movements assessed by the mother are often called kick counts. Fetal movement is associated with healthy fetal condition, and daily evaluation of these movements provides a way of evaluating the fetus. The pregnant client should feel at least ten fetal movements within two hours and will likely feel more movements than that. If the pregnant client notices that they are feeling fewer fetal movements than normal, they should notify their health care provider. The health care provider may recommend tracking the fetus’s movements by doing “kick counts.” Table 9.10b provides instructions on performing kick counts.^[22]

Table 9.10b. Performing Kick Counts^[23]

Nurses teach pregnant clients on how to perform fetal movement counts. The best time to perform FMC is when the fetus is most active. If the fetus does not have a predictable movement pattern, completing the FMC after eating dinner is a good time. To perform this test, the nurse should instruct the pregnant client to lie down on their side or relax in a comfortable chair. Take note of the time. Pay attention only to the movements of the fetus. Count any movement felt, except for hiccups. Any twist, kick, or turn counts as one movement. After ten movements are felt, check the time and record how many minutes it took to feel ten movements.^[25]

If the fetus does not kick or move within one hour, the pregnant client should be instructed to eat or drink something like fruit or juice, lie on their left side, or walk around for five minutes. If the fetus has not moved ten times by the end of the two hours or has a sudden decrease in normal activity, the pregnant client should be instructed to notify their health care provider right away.^[26]