Pocket ObGyn – Antenatal Fetal Testing
See Abbreviations

Goal of Testing

Goal: Measure changes in fetal physiology or behavior w/ suff sens for fetal hypoxemia or acidemia to allow intervention to prevent stillbirth
Primary outcome of interest is a reassuring result to rule out fetal demise w/i 1 w of testing

Indications for antenatal testing
Mat conditions	Fetal conditions
• Antiphospholipid Ab syn • Hyperthyroidism (poorly controlled) • Hemoglobinopathies • Cyanotic heart dz • Systemic lupus erythematosus • Chronic renal dz • Type 1 DM • Hypertensive disorders	• Gestational HTN or preeclampsia • Decreased fetal mvmt • Oligoor polyhydramnios • Intrauterine growth restriction • Postterm Preg • Isoimmunization • Prev fetal demise • Multi gest w/ signif growth discrep
From Int J Gynaecol Obstet. 2000;68(2):175–185.

Testing Modalities (Obstet Gynecol 2009;113:687)

Fetal mvmt count (“kick count”) (Cochrane Database Syst Rev 2007:CD004909)

Variable protocols, usually 2 h, 3–7´ per week

10 mvmts ® reassuring; insuff evid to recommend this method of surveillance

• Nonstress test

Continuous fetal heart monitoring ´ 20–40 min

At least 2 15 bpm ´ 15 s accelerations (or 10 ´ 10 at <32 w) ® reassuring Occasional, brief variable decelerations do not affect negative predictive value Performance for prediction of stillbirth w/i 1 w: Sens 99.7%, spec 45%

Biophysical profile (From US exam of fetus up to 30 min) Elements (2 points each if nml/reassuring):

Continuous fetal breathing, 1 episode >30 s 3+ fetal limb or body mvmt

1+ episodes of flexion/extension of a limb or hand

2 ´ 2 cm or greater pocket of amniotic fluid (or amniotic fluid index >5 cm) Reactive nonstress test

<6/10 = abn (consider deliv); 6/10 = equivocal (rpt in 6–24 h); >6/10 = reassuring. Prediction of stillbirth w/i 1 w: Sens 99.92%, spec 50%.

Contraction stress test (oxytocin or nipple stimulation to produce 3 contractions in 10 min of >40 s, w/ continuous FHR monitoring)

Negative = No late or signif variable decelerations Positive = Late decelerations w/ >50% of contractions Equivocal = Anything btw “negative” & “positive”

Unsatisfactory = Uninterpretable fetal heart tracing or insuff contraction frequency

Prediction of stillbirth w/i 1 w: Sens 99.96%, PPV 70%

Umbilical artery Doppler velocimetry (US measurement, only indicated in fetuses w/ growth restriction)

Low resistance system should allow forward flow throughout cardiac cycle Absent or reverse end-diastolic flow is a/w increased perinatal mortality (5´

greater w/ reversed flow) (Lancet 1994;344:1664)

• Middle cerebral artery Doppler velocimetry

US measurement of peak systolic velocity, indicated if concern for fetal anemia

Velocity >1.5 MoM has sens for mod/sev anemia 100%, spec 88% (N Engl J Med 2000;342:9). Optimal screening interval likely 1–2 w

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Fetal Lung Maturity Testing by Amniocentesis

General Considerations

Consider testing for planned deliv btw 32 & 39 w
Before 32 w low likelihood of maturity
Test performance worsens at earlier GAs
All tests more accurately predict absence of respiratory distress (w/ mature result) than predict respiratory distress (w/ immature result) (Obstet Gynecol 2001;97:305)