Antepartum
Fetal Assessment
Author
Patricia Hartley,
RNC, MSN is the Education/Employee Health Coordinator at
Purpose
The purpose of
this course is to prepare the healthcare professional to conduct a thorough
antepartal assessment of the fetus.
Objectives
At the completion of this module the learner will be able
to:
identify the indications for Antepartal testing,
describe the parameters of biophysical profile,
identify the difference between reactive and non reactive
non-stress test,
describe positive contraction stress test, and
describe the significance of L/S ratios.
Obstetric care has changed
dramatically over the years as the fetus has become more accessible through the
use of ultrasound, increased knowledge of maternal-fetal physiology and more
treatment options. Perinatal Nurses are increasingly challenged to use
high-technology antepartum fetal assessment testing to provide safe and sensitive
care to high-risk pregnant women and their fetuses. Fetal assessment is part of
the process of providing prenatal care. It involves early identification of
real or potential problems and enables pregnant women to achieve the best
possible obstetric outcome.
Pregnancy provides a unique opportunity to assess a women’s
general health. The objective of routine antenatal laboratory tests is to
recognize an unknown condition. Pregnancy can initiate dramatic changes in
various systems, so routine antenatal laboratory tests help detect alterations
from what is considered normal for pregnancy. Ideally, routine laboratory in
the non-pregnant state would provide a baseline from which to determine the
alterations that occur with pregnancy. The goal is to maintain the health of
the mother in order to assure the well-being of the fetus. Frequently that
luxury is not possible since many women do not seek medical care until they are
already pregnant. Generally routine fetal surveillance through antepartum
monitoring and testing is initiated in the event of a non-reassuring sign or
when indicated by risk problems.
This module provides information on antenatal laboratory
test, biophysical assessment (including ultrasound, the biophysical profile and
daily fetal movement counts) and on biochemical assessment (including
amniocentesis, percutaneous umbilical blood sampling and chorionic villus
sampling). The procedures for non-stress and contraction stress testing and an
overview of other fetal assessment parameters will be discussed.
Blood Analysisis
Blood type and Rh factor – Every pregnant woman must have her
blood type and Rh factor determined. Records of previous determinations have a
5% error rate. If the patient’s blood type is O and/or Rh-negative, it may be
advisable to test the father of the fetus to determine if there may be Rh or
ABO incompatibility if the father is Rh-positive, A, B or AB.
Antibody screen for sensitization – Every pregnant woman must have her
serum screened for antibodies formed from exposure to major or minor blood
group antigens. Exposure may have occurred naturally or from a transplacental
hemorrhage, abortion or blood transfusion. If the screen is positive, the
antibody must be identified and titered.
Hemoglobin (Hb) and hematocrit (Hct) – During pregnancy the blood volume
increases by 30-50%. Since plasma volume increases more than red cell volume.
Hb and Hct will fall. Mild anemia is Hb < 11 gm/dl (Hct 27-33%); severe
anemia is Hb < 9 gm/dl (Hct < 27%). Anemia during pregnancy is usually of
the iron-deficiency type. A folic acid deficient state may co-exist with iron
deficiency. It is recommended to repeat the Hb and Hct at 28 weeks gestation.
Leukocyte count – This test is used primarily as a screen to rule out
leukemia and possible infection. Normal values may reach 16,000 in pregnancy.
Differential smear – This is done primarily to identify the types of
leukocytes, erythrocytes, abnormalities and the adequacy of platelets.
Serology – This test is carried out to diagnose maternal syphilis,
which can affect the fetus. VDRL is a screening test.
Rubella titer – The purpose of this screening test is to determine whether
the mother is susceptible to rubella (titer <1:8) or immune (titer <
Fasting and one-hour blood sugar – Since pregnancy may precipitate
glucose intolerance, it is an ideal time to screen for diabetes. The following
risk factors can be used to select patients for glucose intolerance screening:
·
Age
> 25 years
·
Family
history of diabetes
·
Glycosuria
·
Previous
infant with congenital anomalies
·
Previous
fetal or neonatal death
·
Previous
infant > 4, 000 gm
·
Polyhydramnios
·
Fetal
size large for dates
Repeat test
may be done at 28 weeks.
Alpha -Fetoprotein – Screening for neural tube defects is done
at 14-18 weeks. Open neural tube defects leak α-fetoprotein through
the meninges into the adjacent amniotic fluid. This produces high levels of
amniotic fluid α-fetoprotein generally >5 SD above the mean. The high
amniotic fluid levels of AFP are also reflected in maternal serum. False
elevations may occur with erroneous dates, twins, intrauterine demise
Urine Tests
Urinalysis must be performed on
clean-catch specimens. The following tests can identify patients with
asymptomatic kidney or bladder disease:
Microscopy – Microscopic
examination of a centrifuged specimen can identify bacteria, leukocytes, and
erthrocytes, which may indicate infection. Casts and/or red cells may indicate
chronic pyelonephritis. A complete urinalysis should be repeated at 28-30
weeks.
Glucose – Glycosuria
may occur in pregnancy because of increased glomerular filtration rate.
However, it may also indicate carbohydrate intolerance. The test should be
repeated; if positive (≥1+), further testing should be carried out.
Repeat this test at each visit.
Protein – A value over 1+ is abnormal. The cause should be identified (urinary
tract infection, pregnancy-induced hypertension, renal disease).
Leukocyturia – The
leukocyte esterase reagent test strip is helpful in identifying patients with
significant leukocyturia. Current opinion is that the test strip could reduce
screening costs by replacing microscopy.
Cervical
Evaluation
Pap smear – This
identifies cancer of the cervix and cervical herpes. A positive smear requires
further evaluation.
Cultures for gonorrhea, herpes
and group B streptococci – These cultures are recommended if there is
history of previous positive cultures or if the patient is at risk.
Ultrasound
Ultrasound has many uses in
obstetrics. There are three levels of ultrasound in obstetrics – limited, basic
and comprehensive. Guidelines for the use of limited ultrasound by nurses have
been developed by the Association of Women’s Health, Obstetric and Neonatal
Nurses (AWHONN). The limited exam is used for the following:
·
Assessment of amniotic fluid volume
·
Biophysical profile parameters
·
Identification of fetal cardiac activity
·
Location of placenta
·
Confirmation of fetal presentation
·
Certain procedures such as amniocentesis and external
cephalic version
The
basic examination is the most common ultrasound during pregnancy and
includes:
·
Fetal number
·
Presentation
·
Documentation of cardiac activity
·
Placental location
·
Amniotic fluid volume
·
Assessment of gestation age – based on standardized fetal
biometrics
·
Anatomical survey of the fetus for malformations
·
Evaluation of the maternal adnexa
·
If abnormalities are suspected on previous examination or
there is a suspected abnormality based on history or physical exam
Usually
an abdominal or pelvic exam can determine fetal lie. In an obese patient or one
who is difficult to examine it is sometimes impossible to determine whether the
fetus is in a breech or vertex presentation or transfer lie. Ultrasound exam
can readily determine fetal presentation. The
·
Estimation of gestational age for patients with uncertain
dates or verification of dates for those who will have elective termination or
delivery of pregnancy
·
Evaluation of fetal growth
·
Vaginal bleeding in pregnancy
·
Suspected ectopic pregnancy
·
Identification of multiple gestation
·
Diagnosis of molar pregnancy
·
Detection of certain fetal abnormalities
·
Detection of Hydramnios and oligohydramnios
·
Diagnosis of fetal death
·
Suspected abruption
·
Confirmation of fetal lie, position, and presenting part
·
Guidance for amniocentesis
·
Biophysical evaluation
·
Amniotic fluid index
·
Observations of intrapartum events
·
Estimation of fetal weight in preterm labor
·
Follow-up of identified problems
·
History of previous fetal anomaly
·
Evaluation of late registrants for prenatal care
Biophysical
Profile
The
BPP is a noninvasive, dynamic assessment of the fetus and fetal environment.
The assessment is performed using real time ultrasound and the electronic fetal
heart rate monitor. Parameters measured in this evaluation include:
·
Fetal breathing movements
·
Fetal movement
·
Fetal tone
·
Amniotic fluid index
·
Nonstress test (NST)
FHR
(fetal heart rate) reactivity, fetal movement, fetal breathing movements and
fetal tone are acute biophysical markers and are believed to be initiated and
regulated by complex, integrated mechanisms of the fetal central nervous
system. Normal biophysical activity is indirect evidence that the portion of
the CNS that controls that specific activity is intact. The absence of
biophysical activities is difficult to interpret because it may reflect
pathological depression or normal fetal periodicity. The measurement of
amniotic fluid index is a marker of chronic fetal condition.
Investigators have shown an inverse
relationship between non stress test (NST) and amniotic fluid index (AFI)
findings. The lower the AFI the greater the incidence of non-reactive test,
decelerations or perinatal morbidity or mortality.
Biophysical Profile Scoring
|
Biophysical Variable |
Normal (Score = 2) |
Abnormal (Score = 0) |
|
Fetal
breathing movements (FBM) |
At least one episode of
FBM of at least 30 sec duration in 20-minute observation |
Absent FBM or < 30 sec
of sustained FBM in 20 minute |
|
Fetal
movements (FM) |
At least three discrete
body/limb movements in 20-minute (episodes of continuous movement considered
as a single movement) |
Two or fewer episodes of
body/limb movements in 20 minutes |
|
Fetal
tone (FT) |
At lease one episode of
active extension with return to flexion of fetal limb or trunk; opening and
closing of hand considered normal tone |
Either slow extension
with return to partial flexion or movement of limb in full extension or
absence of fetal movement |
|
Amniotic
fluid index (AFI) (varies by gestational age) |
Sum total of measurements
in cm from each quadrant is 5.1 to 24 cm (low normal is 5.1 to 9.9 cm) |
Sum total of measurements in cm from each quadrant is
≤ 5 cm or > 24 cm |
|
Non-Stress
Test (NST) |
Reactive – two or more
episodes of FHR acceleration ≥ bpm ≥ 15 sec |
Non reactive |
Management
guidelines are based on the BPP score and are as follows:
Score Action
10 Repeat weekly; indicates
fetus at minimal risk for fetal damage or death within 1 wk; repeat twice
weekly if > 42 weeks gestation or diabetic
8
Repeat
weekly; consider delivery if oligohydramnios present; repeat twice weekly if
> 42 weeks or diabetic
6
Consider
delivery if fetus mature or if oligohydramnios present; if fetus is immature,
repeat BPP in 24 hours
4
Deliver unless very immature; repeat
in 24 hours
2
Deliver;
score has been associated with a perinatal mortality rate of 60% or greater
Amniotic Fluid
Index
Amniotic fluid index is
calculated by adding the largest vertical pockets of amniotic fluid in the four
quadrants of the gravid uterus:
Ø
>
24 cm – increased is an indication for antepartum testing, including serial AFI
measurements at least weekly. A complete ultrasound examination should be
conducted to evaluate for associated fetal and placental anomalies, as well as
for workup of polyhydramnios, including infection, diabetes and
isoimmunizations.
Ø
10
to 24 cm – normal is a reassuring finding during fetal testing
Ø
5.1
to 9.9 cm – low normal should be evaluated taking into consideration the
gestational age of the fetus. Because amniotic fluid volume peaks at 34 to 35
weeks gestation, an AFI of less than 10 cm should be reevaluated by additional
measurements for the presence of associated conditions such as intrauterine
growth retardation. A borderline value of 5.1 to 7.0 should be reevaluated
every 3 to 4 days if all other findings remain normal
Ø
≤
5 cm – decreased AFI values of 5 cm or less in a patient at term or post term
indicate the need to deliver the fetus. When no amniotic fluid is found, a
complete ultrasound examination should be conducted to rule out fetal
anomalies. Rupture of the membranes maybe a cause for decreased or absent
amniotic fluid.
Fetal Movement
The number of fetal movements
decreases from early to late pregnancy in normal gestation. In pregnancies
complicated by uteroplacental insufficiency, there is marked decrease in daily
fetal movement count and a precipitous fall occurs in the period immediately
preceding fetal death. Though the accuracy and reliability are variable.
The
advantages of fetal movement counting are:
- Inexpensive
- Continuously available
- Relatively simple for patients
to do
Parameters for normal daily fetal
movement counts vary slightly from 3 to 10 in 1 hour to 3 in 30 minutes. Procedure varies with time of day,
reference to mealtime, maternal position and hydration. The patient is
instructed to be quiet, relaxed but awake, with an empty bladder, she places
her hands on her abdomen and focuses on baby’s movements. It is sometimes
helpful to use palpation to verify with the patient what sensations can be
interpreted as fetal movement. Patients should continue to be aware of fetal
movements and report the hourly observations if she perceives decreased fetal
movement. It is important to note that fetal movement can occur without
maternal recognition. A non-stress test is often performed if only one or two movements
are felt within a 1-hour period. If the NST is reactive, further testing may
not be done unless there are some other risk factors or if the patient again
perceives a decrease in fetal movement. A non-reactive NST would be followed as
soon as possible by a biophysical profile or contraction stress test.
Umbilical
Artery Doppler Velocimetry (UADV)
UADV is a non-invasive technique
used to assess the hemodynamics of vascular impedance. A high velocity
umbilical artery diastolic flow is typically found in normally growing fetuses,
whereas diminished flow is found in intrauterine growth retarded fetuses. The
flow can be absent or even reversed in some cases of extreme intrauterine
growth restriction. Abnormal flow velocity waveforms have been correlated with
fetal hypoxia and acidosis and high perinatal morbidity and mortality. The flow
indices generally measured are:
·
Systolic to diastolic ratio
·
Resistance
index
·
Pulsatility
index
An abnormal
flow is either an absent end diastolic flows or a flow index greater than 2
standard deviations above the mean for gestational age. Surveillance of
suspected intrauterine growth restriction with umbilical artery Doppler
velocimetry can achieve equivalent fetal and neonatal outcomes as primary
antepartum surveillance based on the Non-Stress Test.
Fetoscopy
Direct visualization of the fetus
can be done with an endoscope inserted into the amniotic cavity through the
maternal abdomen. The procedure is done to directly view portions of the fetal
anatomy in patients whose fetuses are at high risk for suspected abnormalities.
Fetoscopy has been used for directing skin biopsies
and less frequently to obtain fetal blood in the diagnosis of fetal
hemoglobinopathies. Fetoscopy may be used as an adjunct to laser ablation of connecting
vessels in twin-twin transfusion syndrome. Real-time ultrasound is used during
the procedure to guide the fetoscope to an appropriate area for viewing or
blood sampling.
Fetoscopy is generally performed at 18 weeks
gestation. Complications of this procedure are spontaneous abortion, preterm
delivery, leakage of amniotic fluid, amnionitis and intrauterine fetal death.
An analgesic
may be given to the patient to limit fetal movements during the procedure.
Post-procedure care includes monitoring of vital signs, administration of
anti-Rh globulin as indicated, and teaching patients to report any pain,
bleeding, amniotic fluid loss or fever.
Amnioscopy
Amnioscopy is direct visualization
of amniotic fluid through the fetal membranes with a cone-shaped hollow tube
when the cervix is sufficiently dilated. It is done to identify meconium
stained amniotic fluid. Amnioscopy is valuable in post date pregnancy when the
possibility of post mature syndrome exists. The amnioscope may be used to
visualize the presenting pat after rupture of membranes to obtain fetal blood
sample for blood gas analysis.
Amniography
Amniography is the injection of
radiopaque agents into the amniotic sac to identify Hydramnios,
oligohydramnios, placenta previa, soft tissue silhouette of the fetus and after
a few hours of fetal swallowing – the fetal gastrointestinal tract. The fluid
may become meconium stained after this procedure if the fetus is near term.
Ultrasonography provides most of the same information without using ionizing
radiation or injection of the amniotic sac.
Magnetic
Resonance Imaging (MRI)
MRI is a non-invasive tool that
provides excellent visualization of soft tissue. MRI can be used to evaluate
fetal structures, placental position and density, amniotic fluid quantity,
maternal structures and metabolic or functional malformations.
The time required for the procedure ranges from 20 to
60 minutes, during which the patient must be very still. The procedure provides
very specific information but has limited use because time involved and fetal
movement often makes interpretation difficult.
Radiography
Radiological assessment for fetal
size and maturity and placental localization is seldom done since ultrasound
diagnosis. A simple x-ray film of the abdomen and pelvis after 16 weeks
gestation will most often identify fetal skeletal parts.
During the second half of pregnancy the number of
fetuses can be seen in a multiple gestation. Anencephaly and hydrocephaly can
be identified during the third trimester. Radiography is essentially done only
in non-obstetrical applications such as for an intravenous pyelogram (IVP) or
trauma.
Amniocentesis
Amniocentesis
is the removal of fluid from the amniotic cavity by needle puncture. The
procedure is performed under ultrasound guidance by insertion of a 20 to 22
gauge spiral type needle trans-abdominally to aspirate 5 to 20 ml of amniotic
fluid. This is often performed to assess Lecithin/Sphingomyelin
(L/S) ratio, fetal lung profile and amniotic fluid bilirubin. When genetic problems are
suspected amniocentesis is performed as soon as possible at 16 to 20 weeks to
allow for Karotyping and biochemical studies to be computed before the time
limit for having an elective termination of pregnancy.
Amniocentesis later in pregnancy is
most often performed to assess fetal well-being and maturity. In cases of
isoimmunization the procedure maybe performed repeatedly to monitor the fetal
condition. In high-risk pregnancies such as those with maternal diabetes,
amniocentesis is done to assess fetal lung maturity, indicating the most
opportune time for delivery. There is minimal risk of spontaneous abortion.
Other risks include trauma to fetus or the placenta and bleeding into the
maternal circulation.
Amniotic
Fluid Analysis
Amniotic fluid derives mostly from
fetal urine and secretions and contains fetal cells. The sample is centrifuged
to separate the cells from the fluid. A bloody tap may result in failures of
cell growth and changes the other constituents in the direction of predicting
mature fetus. Green fluid indicates the presence of meconium and interferes
with the reliability of other tests.
Lecithin/Sphigomyelin
(L/S) Ratio
Pulmonary surfactant primarily
contains phospholipids. Surfactant acts as a surface detergent at the
air-liquid interface of the alveoli, preventing their collapse at the end of
expiration. Without surfactant a neonate develops respiratory distress
syndrome, a condition associated with immaturity in which the alveoli of the
lungs literally collapse with each expiration.
The L/S ratio assesses two phospholipids – lecithin and
sphingomyelin – that compose the largest part of the surfactant complex.
Normally during gestation the sphingomyelin are greater than those of lecithin
until about 26 weeks gestation. From 26 to 33 weeks gestation the concentration
of lecithin to sphingomyelin is fairly equal this makes the ratio 1:1. From 34
to 36 weeks there is a sudden increase in lecithin and the ratio rises rapidly.
It is generally accepted that a ratio of 2.0 or greater
indicates pulmonary maturity and decrease the risk of respiratory distress
syndrome. In a macrosomic fetus, as occurs in a diabetic gestation the
association between L/S ratio and RDS is adversely affected. The following
interpretation is generally accepted:
L/S Ratio Fetal Lung Risk for RDS
> 2.0 Mature Minimal
1.5 to 2.0
Transitional Zone Moderate
<
1.5 Immature High
Some stressful conditions during
pregnancy have been known to accelerate fetal lung maturity. They include
pre-eclampsia, prolonged ruptured membranes, narcotic addiction, and
intrauterine growth retardation. This acceleration may be reflex fetal response
to a hostile intrauterine environment. In contrast, conditions in which fetal
lung maturity tends to be delayed include diabetes mellitus and fetal hemolytic
disease.
Acceleration of fetal lung maturity
can be achieved when betamethasone is injected into patients in whom premature
delivery is anticipated. The fetal lung matures, as reflected by a rise in the
L/S ratio usually within 48 hours after initiating therapy.
Lung
Profile
The association between the L/S ratio and the
incidence of respiratory distress syndrome (RDS) does not always hold true in
the diabetic gestation. RDS has been reported in neonates who had mature L/S
ratios. The Lung Profile overcomes the problem of assessing lung maturity in
the fetus of the diabetic and adds a parameter of security when interruption of
pregnancy is contemplated.
The lung Profile measures the interrelationships among the
surfactant phospholipids: the lecithin/sphingomyelin (L/S) ratio, disaturated
(acetone precipitated) lecithin (PL), phosphatidyl inositol (PI), and
phosphatidyl glycerol (PG). Functional maturity of the lung occurs with the
combination of these phospholipids. Phosphatidyl glycerol acts as a lung
stabilizer, and when it is present in diabetic gestations with a mature L/S
ratio, RDS will not occur. Amniostat-FLM is an immunologic test with
agglutination in the presence of phosphatidyl glycerol indicating lung
maturity.
Amniotic Fluid
Bilirubin
During the second half of pregnancy
the concentration of amniotic fluid bilirubin decreases until it virtually
disappears during the last month of gestation. This measurement can be used to
complement other laboratory values in assessing gestational age. It is not
sensitive enough to be used alone for assessing fetal maturity.
Amniotic fluid bilirubin is usually analyzed with a
spectrophotometer measuring the optical density of the specimen against the
characteristic absorption peak at 450 mm. It is important that the specimen of
amniotic fluid not be exposed to light at any time for more than a few seconds,
because this can invalidate the test. Amber glass specimen containers can be
used, or clear test tubes can be covered with occlusive tape to protect the
specimen from light. In Rh-negative-sensitized pregnancies, as identified by
maternal antibody titer (indirect Coombs test), amniocentesis for bilirubin is
one method of evaluating the severity of fetal hemolytic disease.
Percutaneous
Umbilical Blood Sampling (PUBS)
Percutaneous umbilical blood
sampling is achieved through the trans-abdominal insertion of a needle into a
fetal umbilical vessel under ultrasound guidance. The ideal insertion point is
near the placental insertion. 1 to 4 ml of blood is removed during the
procedure and tested by the Kleinhauer-Betke procedure to ensure that the
specimen is fetal blood.
The blood sample is used for determining Karotyping,
direct Coombs, CBC, fetal blood type, blood gases, acid-base status for
intrauterine growth restriction fetuses, detection of infection, and assessment
and treatment of isoimmunization. Complications are unusual and are due to
blood leakage from the puncture site, fetal bradycardia and chorioamnionitis.
Chorionic
Villus Sampling
Chorionic villus sampling
(CVS) is the trans-cervical or trans-abdominal insertion of a needle into the
fetal portion of the placenta to remove a small tissue specimen. The procedure
is done between 10 and 12 weeks gestation under real-time ultrasound
visualization. The aspiration cannula and obturator are passed through the
cervix with care to avoid rupture of the amniotic sac.
This procedure can be done early in the first
trimester to identify fetuses with genetic defects. Complications are rare but
include vaginal spotting/bleeding, spontaneous abortion, rupture of membranes
and chorioamnionitis. Rh-negative patients should receive Rh immune globulin
because of the possibility of feto-maternal hemorrhage, which could result in
isoimmunization.
Non-Stress
Test (NST)
The basis for the NST to assess
fetal well-being is that the normal fetus will produce characteristic heart
rate patterns. Average baseline variability and accelerations of FHR in response
to fetal movement are reassuring signs. The FHR pattern is assessed by external
monitoring without any stress or stimuli to the fetus. When hypoxia, acidosis
or drugs depress the fetal central nervous system, there may be a reduction in
baseline variability and absence of FHR acceleration with fetal movement.
The pattern can also happen when the fetus is asleep
and it is sometimes necessary to monitor for an extra 20 to 30 minutes until
the fetus is in a more active state. The efficacy of maternal ingestion of food
or fluids to stimulate the fetus has not been established although it is the
practice to feed the mother prior to the test. The advantage of the NST over
the CST (contraction stress test) is that it can be performed in an outpatient
setting.
The following are suggested
guideline for interpretation of the NST:
Reactive test Two or more
FHR accelerations above baseline of at least 15 bpm lasting at least 15 seconds
in a 20-minute period; baseline rate is within the normal range and variability
is average
Non-reactive
test Absence of accelerations of FHR
during the testing period
Inconclusive test Less than one acceleration above the
baseline in a 20-minute period or one that is less than 15 bpm and lasts less
than 15 seconds; variability less than 6 bpm or quality of FHR recording not
adequate for interpretation
The reactive test suggests that the fetus will
be born in good condition if labor occurs in a few days. It should be repeated
twice a week in high-risk patients. The non-reactive test should be followed as
soon as possible by a contraction stress test. Patients with an inconclusive
test may have the NST repeated in several hours or may have a Contraction
Stress Test or biophysical profile.
Contraction
Stress Test (CST)
The CST is a method of determining
feto-placental respiratory reserve by observing the fetal heart rate response
to uterine contractions. CST can be performed with endogenously produced
oxytocin as stimulated by breast and nipple manipulation, or the test can be performed
with an exogenous source of oxytocin administered by IV infusion. CST is
contraindicated:
·
Premature
rupture of membranes
·
Placenta
previa
·
Third-trimester
bleeding
·
Previous
classical cesarean section
·
Multiple
gestation
·
Incompetent
cervix
·
Hydramnios
·
Risk
for preterm delivery
The CST is
highly reliable when it is negative. False negatives are rare. On the other
hand, false positives can occur if Hyperstimulation patterns are unrecognized
or if maternal position is supine resulting in hypotension and late
decelerations. In contrast when there are no late decelerations in a patient in
labor with previous positive CST, it may be indicative a correction of
uteroplacental insufficiency in the interval between the test and labor and not
a false positive. Interpretation of the CST for both nipple stimulation and IV
oxytocin:
1. Negative test Three
uterine contractions in a 10-minute period without late decelerations; there is
usually average baseline variability and accelerations of FHR with fetal
movements
2. Positive test Persistent late
decelerations or late decelerations with more than half the contractions; may
be associated with minimal or absent variability
3. Suspicious test Late decelerations occurring
with less than half the uterine contractions
4. Hyperstimulation Contractions occurring more often
than every 2 minutes or lasting longer than 90 seconds, or if there is apparent
Hypertonus associated with contractions; if no late decelerations occur with
the preceding, the test is interpreted as negative; if late deceleration is
observed during or after excessive uterine activity, the test is not
interpretable and is classified as Hyperstimulation because the stress is
considered enough to exceed even normal uteroplacental reserve
5. Unsatisfactory Quality of the recording is
not sufficient to be sure that no late decelerations are present or where less
than three uterine contractions have occurred in a 10-minute period; the test
is not interpretable and cannot be used for clinical management
Summary
The purpose of Antepartum testing is
used to verify fetal well-being. In the best of circumstances, the results of
antepartum testing would be 100% accurate. However, each test has some level of
error in prediction of fetal condition. Current testing measures accurately
identify the healthy fetus but are not as sensitive in identifying truly
compromised fetuses. A fetus who demonstrates a negative test result is very
likely to be healthy, but the fetus who demonstrates a positive test result is
not as likely to be truly compromised.
Because no test provides complete information
regarding fetal well-being, several tests may be required. Strict protocols
must be followed for the administration, interpretation and timely follow-up of
the test results to avoid litigation.
Fetal Assessment is part of the process of providing
prenatal care. Use of the fetal assessment methods discussed here have led to a
decrease in perinatal mortality in pregnant women with identified risk-factors
for uteroplacental insufficiency. However, half of unexpected fetal deaths
occur in women with low-risk pregnancies without identifiable risk factors that
would make them candidates for antepartum fetal testing.
Early identification of real or potential problems
enables pregnant women to achieve the best possible obstetrical outcome.
Patient education should be included in every aspect of the antepartum testing
and interpretation of those results to improve compliance with therapy.
References
AWHONN Fetal Heart Monitoring Principles and Practice
2nd Edition, Kendall/Hunt Publishing Company, Dubuque (1993)
Douphinee, Joan Drukker, Antepartum Testing: A
Challenge for Nursing, Journal of Perinatal & Neonatal Nursing 1987; 1(1):
29-48 Aspen Publishers, Inc.
Gegor, Carolyn L., and Paine, Lisa L., Antepartum
Fetal Assessment Techniques: An Update for Today’s Perinatal Nurse, journal of
Perinatal & Neonatal Nursing 1992; 5(4): 1-15 Aspen Publishers, Inc.
Murray, Michelle, Antepartal and Intrapartal Fetal
Monitoring 4th Edition, Learning Resources International Inc.
Murray, Michelle, Urbanski, Patricia, Essentials of
Fetal Monitoring, Learning Resources International Inc.
Queenan, John T., and Hobbins, John C., Protocols for
High Risk Pregnancies 2nd Edition, Medical Economics Books, Oradell,
New Jersey (1995)
Tucker, Susan, Mosby’s Fetal Monitoring and
Assessment 4th Edition,