Outpatient
Antenatal Testing
FLAME LECTURE: 54
STELLER 8.25.14
Learning Objectives
Understand the rationale for prenatal outpatient fetal
assessment
 Describe approaches for assessment of fetal well being
 Prerequisites:



FLAME LECTURE 53: Overview of Interpreting Fetal Heart Rate
Tracings
See also – for closely related topics
FLAME LECTURE 54B: The Nonstress Test (NST) and Contraction
Stress Test (CST)
 FLAME LECTURE 56: The Biophysical profile
 FLAME LECTURE 57: Assessment of fetal movement
 FLAME LECTURE 59: Assessment of amniotic fluid volume

Rationale of Prenatal Outpatient Fetal
Assessment

Goals




Detect uteroplacental insufficiency
Prevent stillbirth
Avoid unnecessary iatrogenic preterm delivery
Physiologic basis: The fetal brain is incredibly sensitive to
changes in O2 and pH, and under stress:
 Chemoreceptor response to acidemia [ vagally-mediated
deceleration of the fetal heart rate
 Fetal movements decrease as the fetus attempts to conserve
energy1-2
 Blood flow is directed to the brain, heart and adrenals and away
from the kidneys [ a decrease in renal perfusion [ a decrease
in fetal urine production [ oligohydramnios
1.
Olesen AG. Acta Obstet
Gynecol Scand. 2004.
2. Manning FA. AJOG 1993
Antepartum Fetal Distress Cascade
H
Y
P
O
X
I
A
LATE DECELERATIONS APPEAR
(CST)
ACCELERATIONS DISAPPEAR
(NST)
BREATHING STOPS
(BPP)
MOVEMENT CEASES
(BPP, FMC)
FETAL TONE ABSENT
(BPP)
Porto, Clin Ob Gyn, 1987
A
C
I
D
O
S
I
S
Antenatal Assessment Modalities

Fetal movement (kick) counting

Nonstress test

Contraction stress test

Biophysical profile (BPP) parameters: fetal
breathing, fetal body movements, fetal tone,
amniotic fluid volume
 Modified

BPP (mBPP) = NST + AFI
Umbilical Artery Doppler velocimetry (for IUGR
fetuses only)
Indications for Antenatal Testing
= Risk factors for uteroplacental insufficiency

 Pregnancy
Maternal
 APL
syndrome, SLE
 Grave’s
disease
 Asthma,
poorly controlled
 Hemoglobinopathies
 Cyanotic
 Chronic
 Type
heart disease
renal disease
I DM, Type II DM
 Hypertensive
 AMA
disorders
(usually > 38 y.o.)

 Fetal movement
 gHTN,
Pre-eclampsia
 A2 GDM
 Oligohydramnios/ Poly
 IUGR
 Late-term/Post-term
 Isoimmunization
 Previous unexplained fetal demise
 Monochorionic or discordant twins
 Third trimester vaginal bleeding
Timing of antepartum surveillance

WHEN TO START?

WHY TO START?

HOW OFTEN TO PERFORM?

No large clinical trials to guide
recommendations of initiation and frequency
of testing
THE UCI APPROACH - Initiation
26 wks
32 - 34
40
41
@ Dx
Individualize
DM: DFR
Htn IUGR
Diabetes:
Class BC
Gestation
Diabetes
Post Dates
PIH
Decrease
FM
cHTN, SLE
Immune
disorders
IUGR
Rh Isoimmun
Antiphospholipid
antibody
syndrome
Cardiac,
pulmonary or
renal
disease
Discord.
Twins
Mono-mono
twins
Mono-di
twins
Third
trimester
bleeding
Hematol.
disease
THE UCI APPROACH – Frequency
 Twice
 AFI
 CST
weekly NST with weekly AFI
twice weekly in postdates or AFI < 8.0
alternating w/ NST q3-4 days in DM
 AFI
is not as useful in DM, increased AFI
 Twins
 NST
with IUGR/discordance:
twice weekly, UAD + DVP weekly
 Testing
 NST
< 28 weeks: BPP primarily
is often not reassuring or equivocal due to
neurologic immaturity
REASSURANCE?



Incidence of stillbirth within 1 week after a normal fetal
assessment modality3-5

1.9/1000 NSTs - NPR of 99.8%

0.3/1000 CSTs – NPR of 99.9%

0.8/1000 BPPs – NPR of 99.9%

0.8/1000 mBPPs – NPR of 99.9%

0/214 Dopplers in IUGR fetuses – NPR of 100%6
They do not predict stillbirths related to acute changes in
maternal-fetal status

Abruptio placentae

Umbilical cord accident
Achilles heel is high false positive rate (approx 35% CST, 55% NST)
Abnormal testing… now what?

Fix the offending disease process if possible i.e DKA,
PNA

Perform a ‘back-up’ test (CST, BPP or prolonged
monitoring), or repeat testing in short intervals7
 Ex.



Decreased fetal movement + nonreactive NST
Term: CST [ deliver if positive or equivocal
Significantly preterm: BPP [ deliver, continuously monitor or
retest in 24 hours, depending on results
If not reassured, hospitalize and weigh the risks and
benefits of expediting delivery following consideration
of gestational age and the disease state
THE UCI APPROACH: In general
NST + AFI
Both Normal
Nonreactive / AFI < 5
CST
Or
BPP
8
Negative
Retest 3-4 days
Consider delivery
Positive
<6
CFM vs. daily NST
IMPORTANT LINKS

PRACTICE BULLETIN 145 - Antepartum Fetal
Surveillance
OTHER REFERENCES
1.
Olesen AG. Acta Obstet Gynecol Scand. 2004.
2.
Manning FA. AJOG 1993
3.
Freeman RK. AJOG 1982
4.
Miller DA. AJOG 1996.
5.
Manning FA. AJOG. 1987.
6.
Almstrom H. Lancet. 1992
7.
Manning FA. AJOG. 1990.