Outpatient Antenatal TestingFLAME 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

HYPOXIA

ACIDOSIS

LATE DECELERATIONS APPEAR(CST)

ACCELERATIONS DISAPPEAR(NST)

BREATHING STOPS(BPP)

MOVEMENT CEASES(BPP, FMC)

FETAL TONE ABSENT(BPP)

Porto, Clin Ob Gyn, 1987

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 volumeModified BPP (mBPP) = NST + AFI

Umbilical Artery Doppler velocimetry (for IUGR fetuses only)

Indications for Antenatal Testing= Risk factors for uteroplacental

insufficiency Maternal APL syndrome, SLE Grave’s disease Asthma, poorly controlled Hemoglobinopathies Cyanotic heart disease Chronic renal disease Type I DM, Type II DM Hypertensive disorders AMA (usually > 38 y.o.)

Pregnancy 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 - Initiation26 wks 32 - 34 40 41 @ Dx Individualize

DM: DFR Htn IUGR

Diabetes: Class BC

Gestation Diabetes

Post Dates PIH DecreaseFM

cHTN, SLE Immune disorders

IUGR Rh Isoimmun

Antiphos-pholipid 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 weekly NST with weekly AFIAFI twice weekly in postdates or AFI < 8.0

CST alternating w/ NST q3-4 days in DMAFI is not as useful in DM, increased AFI

Twins with IUGR/discordance:NST twice weekly, UAD + DVP weekly

Testing < 28 weeks: BPP primarilyNST 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

Nonreactive / AFI < 5 Both Normal

Retest 3-4 days

CST BPPOr

8

Positive < 6

Consider delivery

CFM vs. daily NST

Negative

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.