Diagnostic Tests

Sandy Warner RNC-OB, MSNCarrie Hallett- Voss, RNFA

NST - Non Stress Test

Evaluation of FHR pattern in the absence of regular contractions to determine fetal oxygenation, neurological and cardiac function

Non Stress Test (NST)

NST became popular as primary surveillance in mid 1970’s due to simplicity and shorter testing

Currently a reactive pattern is defined as 2 accelerations in 20 minutes that reach 15bpm or greater above BLFHR and lasts 15 seconds or greater

NST Definition

Reactive NST indicates less than 1% chance of fetal death within 1 week unless there is a catastrophic event

Accelerations may occur either spontaneously or in association with fetal movement

NST done to determine the adequacy of fetal oxygenation and (CNS) autonomic function

Non Stress Test: Benefits to patient

non-invasive easy, inexpensive, fast no known contraindications good screening test

Non Stress Test (NST) Accelerations indicate intact

neurological functioning between the fetal CNS and the fetal heart

Pathway may be disrupted by: Fetal sleep Fetal hypoxia Drugs (BTMS, ETOH, beta blockers, muscle

relaxants, & CNS depressants) Congenital fetal anomalies

Non Stress Test (NST) 50% of fetuses will be reactive by

26-28 weeks 85% of fetuses will be reactive by

28-32 weeks KEYPOINT:

Once fetus has had a reactive tracing (15 X 15) the same reactivity is

expected in further NSTs.

Indications for NST for High Risk Conditions

high risk for utero-placental insufficiency (smokers, HTN, diabetes, autoimmune disease)

post dates motor vehicle accident (MVA) previous stillbirth IUGR decreased fetal movement isoimmunization if other tests suggest fetal compromise routine

Reactive Non Stress Test

Arrows above from pushing the MARK buttonIndicating mother’s perception of fetal movement

FM and Accelerations 15 X 15

NST Regimen

1986 study by Boehm showed that by increasing NST to 2 times a week, the corrected stillbirth rate dropped from 6.1 /1000 to 1.9/1000 after a reactive NST

Twice a week for high risk (post dates, HTN, IUGR, IDDM)

Once q week for other risk conditions If condition no longer exists, e.g. decreased

fetal movement, continued testing is not required

Same day evaluation for reporting of decreased fetal movement

Non Reactive NST Not necessarily an ominous sign, rather it

does indicate the need for further testing. May be followed by a BPP or a CST If initially non-reactive, prolonging the

period of evaluation usually allows a change in the fetal status and it becomes reactive

Occurs more often in the preterm fetus < 32 weeks due to immature ANS

Non Reactive NST Non Reactive NST

NST

Non reactive NST with good variability probably not an indication for delivery rather, could be related to fetal adaptation to stress

Non Stress Test (NST)

Vibroaccoustic Stimulation (VAS)

Artificial acoustic stimulation

Done after 25 wks gestation when fetus can hear

After 10 minutes of baseline and no accelerations, place the artificial larynx on the maternal abdomen over the fetal head

Vibroaccoustic Stimulation

Provide 5-10 sec stimulation near fetal head, wait one minute

If no acceleration repeat cycle for a total of three times

if non-reactive after 40 minutes, proceed with further evaluation

Vibroaccoustic Stimulation

Fetuses 28 weeks or greater respond to VAS with a consistent increase in heart rate.

Observed changes are greater as term is approached.

Can be used during version to get breech to move from midline spine to lateral spine

Use to startle the fetus to release cord

Contraction Stress Test

A method of observing the response of the FHR to the stress of uterine contractionsA FHR response to 3 spontaneous or induced uterine contractions in 10 minutes may occur:

• Spontaneously• Use of nipple stimulation• Use of Pitocin

The desired result: Negative CST (no late decelerations)

Interpretation: CST Negative: No late or significant variable

decelerations are identified in response to 3 or more contractions lasting at least 40 seconds in a 10 minute window.

Positive: Late decelerations are identified with 50% or more of contractions even if the contraction frequency is less than 3 in 10 minutes.

Interpretation: CST Suspicious : (Equivocal) inconsistent or

occasional late decelerations with less than 50% of contractions. Repeat in 24 hrs.

Tachysystole: Contractions closer than Q2min, or lasting longer than 90 sec, or > 5 contractions in 10 minutes. Repeat in 24 hrs.

Unsatisfactory: the quality of the tracing is inadequate for interpretation or adequate uterine contractions were not achieved.

Limitations of CST

• 30% false positive == unnecessary premature intervention

• conduct in L+D or adjacent area• more expensive, time consuming• must observe after test until

uterine activity has returned to baseline activity level

Tachysystole of uterusToo many UC. Rising restingtonus.

Positive CST

Key Points for Contraction Stress Test

CST now used less frequentlyUterine contractions produce a reduction in blood flow to the intervillous spaces in the placentaA fetus with inadequate placental reserves demonstrates late decelerations in response to hypoxia

Ultrasound

Developed in WWII with submarines

Diagnostic use since 1950s

Definition: transmission of sound waves to investigate an object

(Kline-Fath & Bitters, 2007)

Ultrasound

Advantages: Inexpensive Noninvasive High degree of patient acceptance Yields much information

(Kline-Fath & Bitters, 2007)

Ultrasound Indications Estimation of fetal age

Earlier U/S performed, more accurate Viability Evaluation of fetal growth Location of placenta Fetal presentation in 3rd trimester or

with multiples Anomalies Assessment of amniotic fluid volume

Ultrasound con’t Numerous studies show positive effect on

maternal bonding with ultrasound experience

3D U/S especially helpful in facial anomalies

Nuchal lucency and nasal bone Used in combination with maternal serum levels to

assess for chromosomal abnormalities (Kline-Fath & Bitters, 2007)

Amniotic Fluid Index (AFI)

AFI = amount of amniotic fluid measured in largest pocket in each quadrant ( sum of 4 quadrants)

Normal = 9-10 cm Borderline = 5-8cm Oligohydramnios < 5cm Polyhydramnios > 25cm

Biophysical Profile (BPP) “Intrauterine Apgar Score” Combines ultrasound and NST Fetal activities observed result

from complex processes that are controlled by the CNS

Activities that are first to develop are last to disappear when asphyxia occurs

1. Reactive NST (within 1 hour of ultrasound portion of test)

2. Amniotic Fluid: at least one deepest vertical pocket > 2cm

3. Movement- at least three episodes of gross body movement within a 30 minute period

Five Parameters of Biophysical Profile

Five Parameters of Biophysical Profile

4. Tone- at least one episode of flexion and extension of an extremity within a 30 minute period

5. Fetal Breathing Motions- at least 30 seconds within a 30 minute period

Scoring the BPP

• 2 points for each of the criteria met

• 0 points if the criteria is not met

• reported as: 0/10, 2/10, 4/10, 6/10, 8/10, or 10/10

Interpretation of BPP

• Anytime a (DVP) deep vertical pocket ≤ 2cm, further evaluation is warranted

• score 8/10 (excluding oligo) or 10/10: normal

• score 6/10 : equivocal, repeat within 24 hours

• score 0/10, 2/10, 4/10: delivery is indicated

Keypoints

A deteriorating fetus will lose in this order:

-Reactivity-Fetal breathing

movements-Tone-Movement

Doppler Studies

Definition: Non-invasive study of the blood flow in

the fetus and the placenta

Studies the blood flow of the umbilical cord

More recently may use to look at blood flow in the cerebral artery

Keypoints of Doppler Flow Studies

Doppler waveform analysis can allow identification of a jeopardized fetus before compromises occur.

Umbilical artery observed for flow Ratio number used to measure flow 3.5 in normal, can also be intermittently absent or

absent Reverse diastolic flow is ominous

More Keypoints of Doppler Flow Studies

The change in frequency is called the “Doppler Shift”

This shift is computer analyzed and displayed as a velocity waveform

The frequency of the echoes changes during the systolic and diastolic components of the cardiac cycle

Amniocentesis

Trans-abdominal needle aspiration of 10-20 ml of amniotic fluid for lab analysis

Done under ultrasound

Requires sterile technique and time out

Amniocentesis

Indications: Genetic R/O infection Fetal lung maturity Assess for bilirubin with hemolytic

incompatibility

Amniocentesis

Timing: Early – performed between 11-14 wks

Significantly higher pregnancy loss Post procedure fluid loss

2nd trimester – performed between 15-20 wks

Usually for genetic screening

3rd trimester Usually for fetal lung maturity

(Gilbert, 4th edition, pg 93)

Amnioreduction

Reduces amount of amniotic fluid around fetus

Procedure like amniocentesis only with tubing to suction canister or stopcock

Done to relieve maternal symptoms or with twin to twin transfusion syndrome

Amnioreduction

Fetal Vesicoamniotic Shunt Procedure done for

bladder outlet obstruction

Most common cause is a posterior urethral valve

Predominantly in males Can cause bladder to

lose tone Hydronephrosis Hydroureter Can lead to permanent

damage if not treated by 20 weeks gestation

Fetal Vesicoamniotic Shunt

Fetal Vesicoamniotic Shunt - echotip needle in bladder

Fetal Vesicoamniotic Shunt – post shunt placement and decompression of bladder

Bilateral Hydronephrosis (enlarged kidneys)

Cordocentesis / Fetal Blood Transfusion

Blood Transfusion for anemia

How much blood is given?

Graph is used correlating the hematocrit of donor blood to the hematocrit of the fetus to determine donor blood volume to be given

Cordocentesis / Fetal Blood Transfusion

Fetal MRI Superior soft tissue contrast test Does not use radiation Used for fetal brain, spinal deformities,

lesions, masses Also can assess placental and cord

malformations Also used to measure lung volume

Research still continuing for PPROM pts (Kline-Fath & Bitters, 2007)

Fetal MRI Con’t Not recommended in first trimester

(no documented studies on harm from heat or sound, but not recommended)

Not used routinely, only after U/S not able to detect

Contrast dye not recommended

Informed consent (Kline-Fath & Bitters, 2007)

Fetal Echocardiogram Timing: between 18-22 weeks Indications:

Family history congenital heart defects Maternal diabetes Drug exposure Teratogenic exposure Chromosomal abnormalities Non-immune hydrops Maternal PKU Fetal arrhythmias

Queenan, Hobbins & Spong (4th edition, 2007)

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