NSG210 Exam 2 Reading Outline - Durham Ch. 6: Antepartal Tests

Source: Durham & Chapman, Davis Advantage for Maternal-Newborn Nursing, Chapter 6 (~/Documents/texts/nursing/NSG210/exam02/DURHAM_OB_CH06.pdf). Part of nsg210-exam-2-readings-outline.

Learning Outcomes

1. Define terms used in antenatal tests.
2. Identify the purpose and indication for key antenatal tests.
3. Describe procedure, interpretation, advantages, and risks of common tests.
4. State nursing responsibilities for each test.
5. Identify patient teaching needs.

Nursing diagnoses: deficient knowledge, anxiety, grief (abnormal results), risk for disturbed maternal-fetal dyad (fetal injury from invasive tests).

I. Indications for Antepartum Fetal Surveillance (Table 6-1)

• Maternal conditions: antiphospholipid syndrome, hemoglobinopathies, hypertensive disorders, renal disease, cardiac disease, lupus, insulin-treated diabetes, hyperthyroidism
• Pregnancy-related conditions: gestational hypertension, preeclampsia, gestational diabetes, decreased fetal movement, oligohydramnios or polyhydramnios, fetal growth restriction, multiple gestation with growth discrepancy or monochorionic diamniotic twins, post-term pregnancy, previous unexplained fetal demise, isoimmunization, fetal anomalies

II. The Nurse’s Role in Antepartal Testing

A. Assessment for Risk Factors

• Biophysical - from mother or fetus: genetic, nutritional, medical, obstetric
• Psychosocial - maternal behaviors: smoking, alcohol, drugs, psychological status
• Sociodemographic - access to care, age, parity, marital status, income, ethnicity
• Environmental - workplace or environmental hazards: chemicals, radiation, pollutants
• Many risk factors are cumulative

B. Informed Consent (Critical Component)

• The provider (MD or CNM) performing the procedure has the legal duty to obtain informed consent and cannot delegate the teaching about risks, benefits, and alternatives
• The nurse’s role is patient advocate and witness to the signature, confirming:
  • Consent is voluntary, without coercion
  • The patient has capacity (lucid, competent)
  • All relevant information was disclosed
• If the nurse has concerns, the consent should not be witnessed
• Shared decision-making - discuss risks and benefits in the context of the patient’s values
• Timely reporting of results is essential; delays limit options

C. Nursing Actions for Any Antenatal Test

• Promote informed decisions; assess risk factors
• Build trust; explain how the test is done, what it measures, risks and benefits, what to expect; encourage questions; give online resources (ACOG, AWHONN, March of Dimes, NSGC)
• Comfort: positioning, modesty, privacy
• Reassure; address pain and effects on the baby; allow support person to stay
• Psychological support: cultural awareness, stay with the woman, reduce anxiety, allow venting of frustration with the demands of a high-risk pregnancy
• Document, report results, schedule follow-up, reinforce the provider’s explanation of results

III. Screening vs Diagnostic Tests

• Current ACOG recommendation: offer all patients both screening and diagnostic options, regardless of risk

IV. Genetic Tests

• Goal: detect problems affecting the woman, fetus, or newborn and support informed decisions about pregnancy management
• Aneuploidy - extra or missing chromosome (most common abnormality of chromosome number); differs from polyploidy (whole extra set, e.g., triploidy)
• Haploid - one set of chromosomes (egg or sperm); two haploid cells form a diploid zygote
• Mosaic - abnormal chromosome number not present in all cell lines
• Leading indication for diagnostic testing is possible fetal chromosomal abnormality; karyotype from amniocentesis or CVS cells takes 7-14 days
• Cell-free DNA is still a screening test, not diagnostic
• Testing cannot detect every abnormality, and results cannot predict every outcome (phenotypes vary)
• Benefits: reassurance, prenatal treatment, planning delivery location and staff, option of termination
• Increased risk of a fetal genetic disorder:
  • Maternal age over 35 (aneuploidy)
  • Paternal age 40-50 or older (single-gene disorders)
  • Parent carries a chromosome rearrangement or has aneuploidy or mosaicism
  • Prior child with a structural birth defect, trisomy, or sex chromosome aneuploidy
  • Parent affected by or carrying a genetic disorder
  • Structural anomalies on ultrasound
• If a diagnosis is made: family education, obstetric management plan (surveillance, monitoring, mode of delivery), referral to pediatric specialists and tertiary center, adoption or termination options, perinatal palliative care

V. Biophysical Assessment

A. Fetal Ultrasound

• High-frequency sound waves produce an image; no known risk; imaging method of choice in pregnancy
• ALARA principle - as low as reasonably achievable; only for a valid indication
• Keepsake images or sex determination without medical indication is not recommended
• Types:
  • Standard - fetal presentation and number, amniotic fluid volume, cardiac activity, placental position, biometry, anatomic survey
  • Limited - answers a specific question (e.g., fetal heart activity or presentation in a laboring patient, fluid volume, cervix, viability)
  • Specialized (“detailed” or “targeted”) - increased anomaly risk; includes fetal Doppler, BPP, fetal echocardiography; indications include fetal growth restriction and multiples
  • Point-of-care - at the bedside; RNs with training can do limited exams (presentation, BPP, fluid)
• Uses by trimester (Table 6-2):
  • First - confirm intrauterine pregnancy, cardiac activity, gestational age, multiples, chorionicity; detect missed abortion, ectopic, molar pregnancy; evaluate bleeding; guide CVS; nuchal translucency
  • Second - confirm dates, viability, number, position, anomalies (best after 18 weeks), growth restriction, placental location; guide diagnostic tests
  • Third - growth, position, placental problems (previa, abruption), BPP and AFI, Doppler, bleeding, guide external version
• Procedure:
  • Transvaginal - lithotomy position, sterile covered probe; earlier visualization in the first trimester; used if transabdominal is inconclusive; check for latex allergy
  • Transabdominal - supine; full bladder needed in the first half of pregnancy to lift the uterus out of the pelvis
• Interpretation:
  • Gestational age from crown-rump length, biparietal diameter, femur length; most accurate before 14 weeks (plus or minus 1 week)
  • Nuchal translucency (NT) - fluid space at the back of the fetal neck in the first trimester; 3.0 mm or more (or above the 99th percentile) is linked to aneuploidy and structural defects such as cardiac anomalies
• Nursing actions: explain sound waves, latex check, gown and positioning, pillow and warm blanket, modesty, support, follow-up, documentation
• AWHONN (Box 6-2): nurses doing limited obstetric ultrasound need at least 8 hours of didactic content plus clinical competency; no certification required

B. 3D and 4D Ultrasound

• Many images at once; shows facial features, placental vessels, cord insertion
• Adjunct to conventional ultrasound; possible benefit for facial anomalies, NTDs, tumors, skeletal defects
• No proven clinical advantage in general prenatal diagnosis; no known harm; often requested by parents

C. Magnetic Resonance Imaging (MRI)

• Detailed multi-plane imaging without iodinated contrast; used when screening suggests an abnormality
• Best for complex anomalies (brain, thorax, GI, GU) and abnormal placentation (accreta)
• Procedure: remove all metal; supine with left lateral tilt
• Nursing: explain, address claustrophobia and fear of equipment

D. Doppler Flow Studies (Doppler Velocimetry)

• More than 40% of fetal cardiac output goes to the placenta; placental vascular damage raises resistance and leads to fetal hypoxemia
• Sequence of deterioration: increased umbilical artery resistance, then decreased middle cerebral artery (MCA) resistance (brain-sparing), then abnormal ductus venosus flow
• Umbilical artery Doppler:
  • Measures resistance to blood flow in the placenta; poor placental function reduces diastolic flow
  • Used with NST and BPP to manage fetal growth restriction; serial studies after FGR is diagnosed; improves outcomes in FGR
  • Not a screening tool for the general obstetric population
  • Abnormal: systolic/diastolic ratio above the 95th percentile, or absent or reversed end-diastolic flow (linked to perinatal death; affects timing of delivery)
  • Also used in twin-to-twin transfusion syndrome
  • Best done during fetal apnea (maternal position, FHR, and fetal breathing alter waveforms)
• MCA Doppler - peak systolic velocity above 1.5 times the median predicts moderate or severe fetal anemia (e.g., isoimmunization)
• Brain-sparing - with chronic hypoxemia the fetus redirects cardiac output to the brain
• Cerebroplacental ratio (CPR) - MCA pulsatility index divided by umbilical artery pulsatility index; predicts adverse outcomes in growth-restricted fetuses
• Ductus venosus Doppler - absent or reversed late-diastolic flow indicates advanced compromise, acidemia, and higher mortality
• No risk; nursing: explain, support, follow-up

VI. Biochemical Assessment

More than 15% of pregnancies are at enough risk to warrant invasive testing.

A. Chorionic Villus Sampling (CVS)

• Aspiration of a small amount of placental tissue (chorionic villi) for chromosomal, metabolic, or DNA testing
• Timing: 10-13 weeks; not recommended before 10 weeks
• Procedure: transcervical (lithotomy) or transabdominal (supine) with ultrasound guidance; no significant difference between routes
• Results in about 1 week (5-7 days vs 7-14 for amniocentesis)
• Advantage over amniocentesis: done earlier, results sooner, more management options
• Risks: fetal loss about 0.22% (1 in 455) from bleeding, infection, ROM; 10% have some bleeding afterward; possible increased transmission of hepatitis B, hepatitis C, HIV
• Nursing: explain, breathing and relaxation, position, comfort, label specimens, check FHR twice in 30 minutes after, teach to report cramping, fluid leakage, bleeding, fever, chills; RhoGAM for Rh-negative women

B. Amniocentesis

• Needle through the abdominal wall into the uterus to withdraw amniotic fluid; the most common way to get fetal cells for genetic testing
• Other uses: fetal lung maturity, hemolytic disease, intrauterine infection, therapy for polyhydramnios
• Timing: usually 15-20 weeks for genetic testing
• Procedure: detailed ultrasound locates the placenta and a fluid pocket; ultrasound-guided needle; local anesthetic; full bladder may be needed before 20 weeks
• Accuracy 99%; chromosome results within 2 weeks
• Other results: elevated bilirubin means fetal hemolytic disease; positive culture means infection
• Fetal lung maturity (not recommended as a sole reason for amniocentesis):
  • L/S (lecithin/sphingomyelin) ratio over 2:1 - mature; under 2:1 - immature, RDS risk
  • Phosphatidylglycerol (PG) present - mature; absent - immature
  • Lamellar body count 50,000/microL or more - mature; 15,000 or less - immature; affected by meconium, blood, mucus, hydramnios
• Risks: loss rate about 0.1-0.3%; fetal or placental trauma; bleeding or fluid leakage in 1-2%; preterm labor; maternal infection; Rh sensitization; possible increased transmission of hepatitis B, C, HIV
• Nursing: reassure that ultrasound guides the needle; breathing techniques; antiseptic prep; label specimens; monitor FHR after; teach to report cramping, fluid leakage, bleeding, decreased fetal movement, fever, chills; no heavy lifting for 2 days; RhoGAM for Rh-negative women

C. Fetal Blood Sampling / Percutaneous Umbilical Blood Sampling (PUBS, Cordocentesis)

• Needle into the umbilical vein near the placental insertion to withdraw fetal blood
• Uses: metabolic and blood disorders, fetal infection, rapid karyotype; also therapy (RBC and platelet transfusions)
• Timing: usually after 18 weeks, after ultrasound finds an anomaly
• Results within 48 hours
• Risks: cord bleeding or hematoma, maternal-fetal hemorrhage, fetal bradycardia, infection; overall procedure-related fetal death rate 1.4%; not used when amniocentesis or CVS would give the answer
• Nursing: explain; lateral or wedged position (avoid supine hypotension); have terbutaline ready in case of contractions; external fetal monitoring for 1-2 hours after; teach fetal movement counting

VII. Maternal Assays (Screening)

A. Cell-Free DNA

• Analyzes fetal DNA fragments in maternal blood from about 9-10 weeks
• Most sensitive and specific screening test for common aneuploidies, but false positives and negatives occur; not diagnostic
• Only lab screening test that identifies fetal sex and sex chromosome aneuploidies

B. Maternal Serum Alpha-Fetoprotein (MSAFP)

• AFP is made by the fetal liver, GI tract, and yolk sac
• Screens for neural tube defects and ventral abdominal wall defects; routine because 95% of NTDs occur without risk factors
• Timing: 15-20 weeks
• Increased AFP - NTDs, anencephaly, omphalocele, gastroschisis
• Decreased AFP - trisomy 21 (Down syndrome)
• Detects 80-85% of open NTDs and abdominal wall defects, 90% of anencephaly
• High false-positive rate (anxiety): oligohydramnios, multiples, low maternal weight, underestimated gestational age; false low with fetal death, high maternal weight, overestimated gestational age
• Abnormal result leads to amniocentesis, CVS, or ultrasound
• Nursing: educate, support, schedule diagnostic tests, support groups if NTD

C. Quadruple Marker (“Quad”) Screen

• Second-trimester maternal serum test, 15-22 weeks
• Four analytes: hCG, AFP, dimeric inhibin A, unconjugated estriol (uE3), combined with age, weight, race, diabetes status
• Risk for open fetal defects plus trisomy 21 and 18
• Trisomy 21 pattern: low AFP and low estriol; hCG and inhibin A about twice as high
• Detects 80% of trisomy 21 at 5% false-positive rate (text also cites 60-80%); 85-90% of open NTDs
• Triple screen (hCG, AFP, uE3) is less sensitive (69% for trisomy 21)
• Penta screen adds hyperglycosylated hCG
• Note: the text also states “decreased estriol levels are an indicator of NTDs” - elevated AFP is the classic NTD marker; check with your instructor if this comes up
• No risk; nursing same as AFP

VIII. Antenatal Fetal Surveillance

• FHR pattern, fetal activity, and fetal tone are sensitive to hypoxemia and acidemia
• Goal: reduce preventable stillbirths while avoiding unnecessary intervention
• A normal test means fetal death within 7 days is highly unlikely
• Reserved for high-risk pregnancies because of high false-positive rates; testing usually begins at 32-34 weeks

A. Daily Fetal Movement Count (Kick Counts)

• Compromised fetuses reduce activity to conserve oxygen; cessation of movement can precede fetal death
• Proposed for all pregnancies
• Woman lies on her side and counts movements daily for 1-2 hours
• 2-hour approach: 10 distinct movements in 2 hours is reassuring
• 1-hour approach: at or above baseline; 4 movements in 1 hour is reassuring
• If decreased: eat something, rest, focus on movement for 1 hour
• Fewer than 4 movements in 2 hours - report; leads to NST or BPP
• Advantages: inexpensive, no equipment, easy to teach; no risk

B. Nonstress Test (NST)

• FHR accelerations with fetal movement show adequate oxygenation and an intact autonomic nervous system
• Most common method of antepartum surveillance; used for hypertension, diabetes, multiples, trauma, bleeding, decreased movement, placental abnormalities
• Procedure: external FHR transducer and contraction strip for 20-40 minutes
• Reactive (32 weeks or more): 2 or more accelerations of at least 15 bpm above baseline lasting at least 15 seconds within 20 minutes
• Reactive (under 32 weeks): 2 accelerations of at least 10 bpm lasting 10 seconds in 20 minutes
• Nonreactive: not enough accelerations in 40 minutes; follow with BPP or ultrasound
• Repetitive variable decelerations longer than 30 seconds - check amniotic fluid or monitor longer
• High false-positive rate (over 50%); low false-negative rate (under 1%)
• Nursing: void first; semi-Fowler’s or lateral position (avoid aortocaval compression); interpret and report; document time, reason, maternal vitals; testing usually weekly or twice weekly

C. Vibroacoustic Stimulation (VAS)

• Artificial larynx on the abdomen near the fetal head for 1 second; repeat at 1-minute intervals up to 3 times
• Used when the NST is nonreactive, to wake the fetus and tell sleep from hypoxia
• Only when the baseline is normal; not with decelerations or bradycardia
• Reactive: 2 accelerations of 15 bpm for 15 seconds in 20 minutes
• Reduces nonreactive NSTs and testing time; no adverse effects; not routine in high-risk pregnancies

D. Contraction Stress Test (CST)

• Tests whether the fetus maintains a normal FHR when contractions briefly reduce placental blood flow; used after a nonreactive NST at term
• Procedure: monitor 20 minutes; if no spontaneous contractions, nipple stimulation (brush nipples 10 minutes) or IV oxytocin
• Need 3 contractions of more than 40 seconds in 10 minutes
• Negative (normal): no late or significant variable decelerations, moderate variability
• Positive (abnormal): late decelerations with 50% or more of contractions; linked to fetal death, FGR, low Apgars, cesarean, need for resuscitation; follow with BPP
• Equivocal or suspicious: intermittent late or significant variable decelerations; repeat in 24 hours
• High false-positive rate
• Contraindicated with conditions where contractions are unsafe: preterm labor risk, bleeding (previa), uterine rupture risk
• Nursing: void first, semi-Fowler’s, vitals every 15 minutes, safe oxytocin use - avoid uterine tachysystole (more than 5 contractions in 10 minutes, less than 60 seconds between, or a contraction over 90 seconds)

E. Amniotic Fluid Index (AFI)

• Ultrasound measurement of fluid pockets in four quadrants
• Fetal urine is the main source of amniotic fluid and depends on renal perfusion
• Normal: 8-24 cm
• Under 5 cm - oligohydramnios; increased perinatal mortality; chain: decreased uteroplacental perfusion leads to decreased fetal renal blood flow leads to decreased urine leads to oligohydramnios
• Over 24 cm - polyhydramnios; may indicate NTDs, GI obstruction, fetal hydrops
• With NST, a strong indicator of fetal status; no risk; requires ultrasound training

F. Biophysical Profile (BPP)

• “Intrauterine Apgar” - ultrasound plus NST; 5 components scored 2 (present) or 0 (absent) over 30 minutes:

• Acute markers: NST, breathing, movement, tone; chronic marker: amniotic fluid volume
• Scoring:
  • 8-10 - reassuring
  • 6 - equivocal, possible asphyxia; repeat in 12-24 hours or deliver depending on gestational age
  • 4 - nonreassuring, probable asphyxia; further evaluation, consider delivery
  • 2 or less - almost certain asphyxia; immediate delivery
• Hypoxia shuts down activities in reverse order of development: the last to develop (FHR reactivity) is lost first; the first to develop (tone and movement) is lost last
• Lower false-positive rate than NST or CST; no risk; usually weekly (twice weekly for some complications)

G. Modified Biophysical Profile

• NST (short-term well-being) plus AFI (long-term placental function); NST and AFI are the most predictive of outcome
• Normal: reactive NST and deepest vertical pocket over 2 cm or normal AFI
• Abnormal: nonreactive NST, or deepest pocket under 2 cm, or AFI under 5
• Fluid changes slowly because the fetus shunts blood to heart and brain and away from kidneys
• Faster than full BPP; usually weekly

IX. Issues in Antepartal Testing

• Nurses have an ethical responsibility to support informed decision-making
• Health literacy and active engagement with providers drive informed choices; use woman-centered, nonjudgmental communication
• Earlier diagnosis creates more complex choices (termination, fetal therapy, waiting for postnatal treatment); families continuing a pregnancy with anomalies need individualized plans through birth and NICU
• Many tests have limited precision and high false-positive rates, so they are better at confirming well-being than diagnosing problems