Chapter 14.Assessment of fetus
A client in her third trimester has come to the clinic for her first prenatal visit. She asks the nurse whether ultrasound can determine the baby's age. What statement by the nurse would be the best response?
"The estimate of gestational age may vary by one to three weeks." Rationale: The ability to establish fetal age accurately by ultrasound is lost in the third trimester because fetal growth is not as uniform as it is in the first two trimesters; however, ultrasound can be used to approximate gestational age within one to three weeks' accuracy during the third trimester. A comprehensive ultrasound is used to detect anatomical defects, not gestational age. Ultrasound is not used to determine gender.
A prenatal client at 30 weeks gestation is scheduled for an amniocentesis to determine fetal lung maturity. The nurse expects the lecithin/sphingomyelin (L/S) ratio to be:
1:1 Rationale: At about 30-32 weeks gestation, the amounts of lecithin to sphingomyelin become equal, an L/S ratio of 1:1. Prior to 30 weeks gestation, the lecithin concentration is less than that of the sphingomyelin (L/S ratio of 0.5:1). After 35 weeks, the lecithin exceeds the sphingomyelin by a ratio of 2:1 or greater.
Contraction stress test (CST)
A method of assessing the reaction of the fetus to the stress of uterine contractions. This test may be utilized when contractions are occurring spontaneously or when contractions are artificially induced by oxytocin challenge test (OCT) or breast self-stimulation test (BSST). Contraindications Preterm labor or women at high risk for preterm labor Premature membrane rupture History of extensive uterine surgery or classical incision for C-section Placenta previa Procedure Placed in supine position, monitor applied Initial recording done to determine if woman is having at least 3 spontaneous contractions within 10 minute time period with duration of 40 seconds are longer. Test not done if spontaneous contractions meet criteria
Umbilical velocimetry
A noninvasive ultrasound test, measures blood flow changes that occur in maternal and fetal circulation in order to assess placental function.
Phosphatidylglycerol (PG)
A phospholipid present in fetal surfactant after about 35 weeks' gestation.
Surfactant
A substance composed of phospholipid, which stabilizes and lowers the surface tension of the alveoli during extrauterine respiratory exhalation, allowing a certain amount of air to remain in the alveoli during expiration.
A client at 28 weeks gestation is admitted to the labor and birth unit. Which test might be used to assess the client's fetal status?
Biophysical profile (BPP) Rationale: Biophysical profile would be used to assess the client's fetal status at 28 weeks gestation. Ultrasound for physical structure is limited to identifying the growth and development of the fetus, and does not assess for other parameters of fetal well-being. Contraction stress test is appropriate in the third trimester. Amniocentesis tests for lung maturity, not overall status.
Ultrasound
High-frequency sound waves that may be directed, through the use of a transducer, into the maternal abdomen. The ultrasonic sound waves reflected by the underlying structures of varying densities allow identification of various maternal and fetal tissues, bones, and fluids.
Interpretation of CST
Interpretation Negative (Reassuring) No late decelerations although the fetus was stressed by 3 contractions of at least 40 secs duration in a 10 minute period Positive (abnormal) Late decelerations accompanying at least 50% of the contractions even when fewer than 3 contractions occur in 10 minutes Equivocal (suspicious)- Intermittent late decelerations and significant variable decelerations (sudden decrease in FHR that quickly return to baseline Equivocal (hyperstimulation) FHR decelerations occurring in the presence of contractions that are occurring every 2 minutes and lasting longer than 90 seconds Unsatisfactory - Fewer than 3 contractions in 10 minutes or a tracing that cannot be interpreted Advantages minimally invasive follow up Provides Reassurance for another week Allows the physician to analyze available options Disadvantages More time consuming Requires precision More costly
Lecithin
Lecithin/sphingomyelin (L/S) ratio Lecithin and sphingomyelin are phospholipid components of surfactant; their ratio changes during gestation. When the L/S ratio reaches 2:1 (also can be reported 2.0), the fetal lungs are thought to be mature and the fetus will have a low risk of respiratory distress syndrome (RDS) if born at that time.
A prenatal client at 22 weeks gestation is scheduled for an amniocentesis. What would be an appropriate nursing action to prepare this client for the procedure?
Position the client in a left lateral tilt. Rationale: An appropriate nursing action to prepare this client for amniocentesis would be to position the client in a left lateral tilt to prevent supine hypotension. The skin is cleansed with povidone-iodine (Betadine), not alcohol. Rh immune globulin is appropriate only for nonsensitized Rh-negative women after the procedure. Encouraging the client to take fluids is not appropriate prior to the procedure, because the client may become nauseous.
Chorionic villus sampling (CVS)
Procedure in which a specimen of the chorionic villi is obtained from the edge of the developing placenta at about 8 weeks' gestation. The sample can be used for chromosomal, enzyme, and DNA tests. Test done at 10-12 wks gestation Counsel women as to risks and benefits 2 methods Transcervical use ultrasound to guide catheter though the cervix to obtain sample Transabdominal With ultrasound guidance the physician inserts a needle though the abdominal wall and myometrium and withdraws a sample of chorionic villi into a syringe with medium Advantages Done earlier than amniocentesis and thus offers earlier prenatal diagnosis Risks: Spontaneous Abortion Infection; bleeding Possibility of limb reduction defects (small but parents must be informed Cramps
Amniocentesis
Removal of amniotic fluid by insertion of a needle into the amniotic sac; amniotic fluid is used to assess fetal health or maturity. Traditionally done at 15-20 weeks gestation Mid Trimester To identify chromosome abnormalities and other genetic defects Third Trimester Determine fetal lung maturity Fetal lung maturity can be obtained by determining the ratio of these 2 components of SURFACTANT(Lecithin/Sphingomyelin ratio Lecithin - phospholipid component of fetal lung fluid Surfactant - reduces surface tension in the alveoli Sphingomyelin - general amniotic membrane lipid) Ratio of 2:1 indicates fetal lung maturity Occurs @ 35 wks
•Fetal lung maturity can be assesed by
The lecithin/sphingomyelin ratio, presence of phosphatidylglycerol, and level of lamellar body counts can be assessed to determine fetal lung maturity.
Quadruple screen
The most widely used test to screen for Down syndrome (trisomy 21), trisomy 18, and neural tube defects (NTDs).
A prenatal client in her second trimester is admitted to the maternity unit with painless, bright red vaginal bleeding. What test might the physician order?
Ultrasound Rationale: An ultrasound for placenta location to rule out placenta previa would be ordered for a client who presents with painless, bright red vaginal bleeding. Alpha-fetoprotein (AFP) is a test used to screen for neural tube defects. A contraction stress test is ordered in the third trimester to evaluate the respiratory function of the placenta. Amniocentesis is a procedure used for genetic diagnosis or, in later pregnancy, for lung maturity studies.
•Maternal assessment of fetal activity can be used
as a screening tool to provide information about fetal well-being.
•Doppler blood flow studies are used to
assess placental function and sufficiency.
•Advantages of CVS include
early detection of certain fetal disorders with a decreased waiting time for results. Disadvantages include an increased risk to the fetus, inability to detect neural tube defects, and the potential for repeated invasive procedures.
•The quadruple screen measures
substances contained in the amniotic fluid that provide information regarding the presence of fetal anomalies, such as neural tube defects and Down syndrome.
Biophysical profile (BPP)
Assessment of five variables in the fetus that help to evaluate fetal risk: breathing movement, body movement, tone, amniotic fluid volume, and fetal heart rate reactivity.
•First trimester combined screening includes
nuchal translucency testing (NTT) and serum tests, which is more accurate than using only the ultrasound screening.
The nurse is reviewing four prenatal charts. Which client would be an appropriate candidate for a contraction stress test (CST)?
A client with intrauterine growth retardation. Rationale: A contraction stress test (CST) is indicated for a client with intrauterine growth retardation (IUGR), because it will assess the respiratory function of the placenta, which may be adversely affected by the conditions causing IUGR. The contraction stress test is contraindicated for the client with multiple gestation, an incompetent cervix, or placenta previa.
Nuchal translucency testing (NTT)
A combination of an ultrasound and maternal serum test that is used to screen fetuses between 11 weeks and 1 day and 13 weeks and 6 days to determine if a fetus is at risk for a chromosomal disorder, such as Down syndrome (trisomy 21) and trisomy 18. Measures fetal neck. greater than 3mm are at risk Uses ultrasound Screening test only- indicates the fetus is at risk Requires further testing to determine a specific diagnosis Non-invasive A normal result can be reassuring
First-trimester combined screening
A comprehensive screening testing that includes the NTT and serum screening for pregnancy-associated plasma protein-A (PAPP-A) and free beta human chorionic gonadotropin (BHCG) to determine if a fetus is at risk for trisomies 13, 18, and 21.
Nonstress test (NST)
An assessment method by which the reaction (or response) of the fetal heart rate to fetal movement is evaluated. Procedure Uses external fetal heart monitor with button attached to monitor Baseline obtained first Semi sitting position best Button pushed whenever fetal movement felt With movement FHR should increase 15 beats per min & remain increased for 15 seconds 15/15 If no increase with movement - poor O2 perfusion of fetus suggested Done for about 40 minutes allowing for fetal sleep-wake cycles
What 5 biophysical varibles are assessed with a biophysical profile?
Fetal breathing movement Fetal movements of body or limbs Fetal tone (extension and flexion of extremities) Amniotic fluid volume index (visualized as pockets of fluid around the fetus) - AFI Reactive FHR with activity (reactive NST)
A prenatal client at 30 weeks gestation is scheduled for a nonstress test (NST) and asks the nurse, "What is this test for?" The nurse correctly responds that the test is used to determine:
Fetal well-being Accelerations of fetal heart rate Adequate fetal oxygenation Rationale: An NST documents fetal well-being by measuring fetal oxygenation and fetal heart rate accelerations, but not fetal lung maturity.
Interpretation of NST
Interpretation Reactive = Acceleration of FHR with fetal movement = Good! At least 2 fetal heart rate accelerations, with or without fetal movement detected by the woman occur within a 20 minute time period, peak at least 15 beats per minute (bpm) above the baseline and at least 15 seconds from baseline to baseline Nonreactive - tracing doesn't demonstrate the required characteristics
The physician orders an ultrasound for a prenatal client prior to an amniocentesis. The nurse explains to the client that the purpose of the ultrasound is to:
Locate the placenta. Rationale: The purpose of the ultrasound before an amniocentesis is to locate the placenta, fetus, and an adequate pocket of fluid. Determination of the gestational sac volume, measuring the crown-rump length, and measuring the biparietal diameter are aspects of assessing fetal well-being (biophysical profile, or BPP), and may or may not be done prior to the amniocentesis, depending on gestational age.
Characteristics of CST
Mirrored FHR decels with contraction - Head compression Late Decels after contraction - Fetus is in destress V or W decels with contraction, cord compression
The nurse is preparing a prenatal client for a transvaginal ultrasound. What nursing action should be included in the preparations?
Place client in lithotomy position. Rationale: After having the client void, assist her to a lithotomy position for a transvaginal ultrasound. Preparation for a transabdominal ultrasound includes encouraging the client to drink 1.5 quarts of fluid, maintaining a full bladder, and applying transmission gel over the client's abdomen.
The nurse is teaching a prenatal client about chorionic villus sampling (CVS). The nurse correctly teaches the client that the risks associated with CVS include:
Rupture of membranes Spontaneous abortion Intrauterine infection Rationale: Risks of CVS include intrauterine infection, rupture of membranes, and spontaneous abortions, as well as Rh isoimmunization and fetal limb defects.
What do doppler blood studies assess?
Umbilical velocimetry Useful in assessing and managing pregnancies with suspected uteroplacental insufficiency before asphyxia occurs Has been associated with: Takes 15 - 20 minutes can be initiated at 16-18 weeks and then scheduled at regular intervals for the woman
•Ultrasound offers
a valuable means of assessing intrauterine fetal growth because the growth can be followed over a period of time. It is noninvasive and painless, allows the certified nurse-midwife or physician to study the gestation serially, is nonradiating to both the woman and her fetus, and has no known harmful effects.
•A contraction stress test (CST)
provides a method for observing the response of the FHR to the stress of uterine contractions. The desired result is a negative test.
•Amniocentesis
can be used to obtain amniotic fluid for genetic testing or for evaluating fetal lung maturity.
•A fetal biophysical profile (BPP)
includes five variables (fetal breathing movement, fetal body movement, fetal tone, amniotic fluid volume, and FHR reactivity) to assess the fetus at risk for intrauterine compromise.
•A nonstress test (NST)
is based on the knowledge that the FHR normally increases in response to fetal activity and to sound stimulation. The desired result is a reactive test.
•Nuchal translucency testing
is used as a tool to screen for trisomies 13, 18, and 21. It is noninvasive and painless, but is not diagnostic in determining if a fetus has an abnormality. Uses ultrasound Screening test only- indicates the fetus is at risk Requires further testing to determine a specific diagnosis Non-invasive A normal result can be reassuring
