Outpatient Antenatal Testing FLAME LECTURE: 54

STELLER 8.25.14

Learning Objectives

u  Understand the rationale for prenatal outpatient fetal assessment

u  Describe approaches for assessment of fetal well being u  Prerequisites:

u  FLAME LECTURE 53: Overview of Interpreting Fetal Heart Rate Tracings

u  See also – for closely related topics u  FLAME LECTURE 54B: The Nonstress Test (NST) and Contraction Stress

Test (CST) u  FLAME LECTURE 56: The Biophysical profile u  FLAME LECTURE 57: Assessment of fetal movement u  FLAME LECTURE 59: Assessment of amniotic fluid volume

Rationale of Prenatal Outpatient Fetal Assessment u  Goals

u  Detect uteroplacental insufficiency u  Prevent stillbirth u  Avoid unnecessary iatrogenic preterm delivery

u  Physiologic basis: The fetal brain is incredibly sensitive to changes in O2 and pH, and under stress: u  Chemoreceptor response to acidemia [ vagally-mediated deceleration of

the fetal heart rate u  Fetal movements decrease as the fetus attempts to conserve energy1-2

u  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

A C I D O S I S

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

u  Fetal movement (kick) counting

u Nonstress test

u Contraction stress test

u Biophysical profile (BPP) parameters: fetal breathing, fetal body movements, fetal tone, amniotic fluid volume u Modified BPP (mBPP) = NST + AFI

u Umbilical Artery Doppler velocimetry (for IUGR fetuses only)

Indications for Antenatal Testing = Risk factors for uteroplacental insufficiency

u Maternal u APL syndrome, SLE

u Grave’s disease

u Asthma, poorly controlled

u Hemoglobinopathies

u Cyanotic heart disease

u Chronic renal disease

u Type I DM, Type II DM

u Hypertensive disorders

u AMA (usually > 38 y.o.)

u Pregnancy u ê Fetal movement

u gHTN, Pre-eclampsia

u A2 GDM

u Oligohydramnios/ Poly

u  IUGR u Late-term/Post-term

u  Isoimmunization

u Previous unexplained fetal demise

u Monochorionic or discordant twins

u Third trimester vaginal bleeding

Timing of antepartum surveillance

u  WHEN TO START?

u  WHY TO START?

u  HOW OFTEN TO PERFORM?

u  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

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

u Twice weekly NST with weekly AFI u AFI twice weekly in postdates or AFI < 8.0

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

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

u Testing < 28 weeks: BPP primarily u NST is often not reassuring or equivocal due to

neurologic immaturity

REASSURANCE? u  Incidence of stillbirth within 1 week after a normal fetal assessment

modality3-5

u  1.9/1000 NSTs - NPR of 99.8%

u  0.3/1000 CSTs – NPR of 99.9%

u  0.8/1000 BPPs – NPR of 99.9%

u  0.8/1000 mBPPs – NPR of 99.9%

u  0/214 Dopplers in IUGR fetuses – NPR of 100%6

u  They do not predict stillbirths related to acute changes in maternal-fetal status

u  Abruptio placentae

u  Umbilical cord accident

u  Achilles heel is high false positive rate (approx 35% CST, 55% NST)

Abnormal testing… now what? u  Fix the offending disease process if possible i.e DKA, PNA

u Perform a ‘back-up’ test (CST, BPP or prolonged monitoring), or repeat testing in short intervals7 u Ex. Decreased fetal movement + nonreactive NST

u  Term: CST [ deliver if positive or equivocal

u  Significantly preterm: BPP [ deliver, continuously monitor or retest in 24 hours, depending on results

u  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 BPP Or

8

Positive < 6

Consider delivery

CFM vs. daily NST

Negative

IMPORTANT LINKS & REFERENCES

u PRACTICE BULLETIN 145 - Antepartum Fetal Surveillance

u Olesen AG. Acta Obstet Gynecol Scand. 2004.

u Manning FA. AJOG 1993

u  Freeman RK. AJOG 1982

u Miller DA. AJOG 1996.

u Manning FA. AJOG. 1987.

u Almstrom H. Lancet. 1992

u Manning FA. AJOG. 1990.