14. Electronic Fetal Monitoring, Imaging, Management of Preterm Labor

Electric fetal monitoring AKA

Cardiotocography

Electric fetal monitoring (cardiotocography)

Continuously records FHR — Allows monitoring of fetus baseline, changes & patterns overtime, response to contractions

**Commonly used during labors

Monitoring devices for electric fetal monitoring (cardiotocography)

External (abdominal transducer) & internal (scalp electrode)

**External requires gel for proper conduction

What are indications for prenatal electric fetal monitoring (cardiotocography)?

- Decreased maternal perception of movement

- Periodic monitoring of high risk pregnancies w/ tocodyndamometry (assesses for contractions)

Nonstress test (NST)

FHR monitoring for accelerations in FHR (indicates fetal movement & wellbeing)

Reactive NST (define)

≥2 FHR accelerations at least 15 bpm above baseline, lasting at least 15 sec, within 20 min monitoring period (for >32 weeks)

**REASSURING

In the event of nonreactive NST...

Abnormal → Additional testing

Biophysical profile (BPP)

- Method to evaluate fetal well-being in high risk patients

- BPP & following via US: Fetal breathing movements (sustained for >30 secs), fetal movement, fetal tone, amniotic fluid volume (NO oligohydramnios)

- ALL within 30 minutes

What type of NST is reassuring?

Reactive NST

Normal FHR baseline (value)

110-160 bpm

Fetal tachycardia (value)

>160 bpm

Fetal bradycardia (value)

<110 bpm

Determining baseline EFM

Mean FHR rounded to increments of 5 bpm during 10 min segment, excluding:

- Periodic changes

- Periods of marked FHR variability

- Segments of baseline that differ >25 bpm

**HR must be at that level for minimum of 2 minutes in any 10 min segment

Each cm on vertical axis (HR) on EFM represents...

30 bpm

Horizontal axis (time) of EFM

- Chart recorder moves at speed of 3cm/min

- Time between each bold line — 1 min

Baseline variability (define)

Irregular amplitude and frequency of baseline FHR fluctuations

**Quantified by amplitude of peak-to-trough in bpm

Absent variability (define)

Amplitude range undetectable

Minimal variability (define)

Baseline fluctuations ≤5 bpm

Moderate (normal) variability (define)

Baseline fluctuations 6-25 bpm

Marked variability (define)

Baseline fluctuations ≥25 bpm

Acceleration (define)

Abrupt increase in FHR (onset to peak within 30 secs)

≥32 weeks GA → Peak of ≥15 bpm with duration of ≥15 secs, less than 2 mins from onset to return

≤32 weeks GA → Peak of ≥10 bpm with duration of ≥10 secs, less than 2 mins from onset to return

Prolonged acceleration (define)

Lasts ≥2 mins BUT less than 10 mins in duration

If an acceleration lasts 10 minutes or longer...

It is considered baseline change

Early decelerations (define)

Symmetrical, gradual decrease & return of FHR associated with uterine contraction

Gradual → Change from onset of decline in FHR to the nadir develops over ≥30 secs

Early decelerations occur d/t...

Head compression

Variable decelerations (define)

Apparent ABRUPT decrease in FHR; Decrease of FHR of ≥15 bpm with duration of ≥15 secs, less than 2 mins from onset to return

When variable decelerations are associated with uterine contractions...

Onset, depth, duration commonly vary with successive uterine contractions

Variable decelerations occur d/t...

Cord compression

Late decelerations (define)

Apparent, symmetrical, gradual decrease & return to FHR associated with uterine contraction; Delayed in time w/ nadir of deceleration after peak & return to baseline after contraction ended

Most causes — Onset, nadir, recovery of deceleration occur after beginning, peak, and ending of contraction

Late decelerations occur d/t...

Placenta insufficiency

Causes of fetal bradycardia

Head compression, fetal hypoxia

Causes of fetal tachycardia

Maternal fever, fetal compromise, cardiac arrhythmia, maternal use of drugs (atropine, terbutaline)

Causes of decreased variability

Fetal acidemia, systemic analgesics or magnesium sulfate during labor

Causes of accelerations

Fetal movement, contractions, temporary umbilical cord occlusion

Causes of early decelerations

Head compression during contractions; Degree of decal proportional to contraction strength

**Considered benign

Causes of late decelerations

Poor uterine perfusion, placenta dysfunction

**Concerning for fetal acidemia if associated with decreased variability

Causes of variable decelerations

Cord compression, changes to oxygenation (may or may not be pathologic)

**Concerning if associated with absent FHR variability

Categories of EFM tracings

Category I: FHR tracings normal

Category II: FHR tracings indeterminate

Category III: FHR tracings abnormal

EFM Category I

Normal — Strongly predictive of normal fetal acid/base status

EFM Category II

Indeterminate — NOT predictive of fetal acid/base status BUT inadequate evidence

- Require eval, continued surveillance, & reeval

EX: Ancillary tests to ensure fetal well-being OR intrauterine resuscitative measures

EFM Category III

Abnormal fetal acid/base status

- Require PROMPT eval & intervention; If does not resolve → Delivery

EX: Interventions — Maternal oxygen, change in maternal positive, d/c of labor stim, tx maternal hypotension, tx tachysystole

Which EFM category is most concerning?

Category III

What is indicated to confirm early pregnancy?

1st trimester US

Indications / Uses for 1st trimester US

- Confirm early pregnancy — Location of gestational sac, told sac, fetal pole

- Estimate GA — Rump length

- Confirm viability — Cardiac activity

- # of gestations — Chorionicity & amnionicity

- Genetic screen — Nuchal translucency

What is recommended in all pregnancies in the 2nd trimester?

Anatomy US at 18-20 weeks

18 → Best for major anatomic anomlies

>20 → Best for heart & brain anomalies

Indications / Uses for 2nd & 3rd trimester US

- Anatomy US — Fetal anomalies

- Assess / monitor growth

- Fetal well-being

- Lie & presentation

- Placental anomalies

- Cervical insufficiency

2nd & 3rd trimester US: Assessing & monitoring growth

Biparietal diameter, HC, abdominal circumference, femoral diaphysis length → Estimate of fetal weight

Indications for assessment & monitoring of growth in 2nd / 3rd trimester

- Fundal height measuring too small/large, unable to accurately assess (multiple gestation)

- Complications that can cause IUGR / macrosomia

2nd & 3rd trimester US: Evaluating fetal well-being

Fetal surveillance to ID fetuses at risk for death / severe morbidity

Methods for evaluating fetal well-being

Biophysical profile — NST, fetal breathing movement, fetal movement, fetal tone, amniotic fluid volume

Doppler US:

- Umbilical A. → Indicator for placental function

- MCA → Indicator for fetal hypoxemia, general well-being, fetal anemia

- Ductus venosus → Indicator for cardiac compliance & placental health

Indications for assessment of fetal well-being in 2nd / 3rd trimester

- Decreased fetal movement

- Known IUGR

- Complications w/ increase risk of severe morbidity

What ultrasounds are most significant throughout a pregnancy?

Confirm early pregnancy & anatomy scan

Benefits of 3D US

Closer eval of suspected anomaly from 2D US

Leading cause of neonatal morbidity & mortality

Preterm labor

Preterm labor (define)

Contractions associated with cervical change from 20 to 37 weeks GA

**Can also occur with preterm premature rupture of membranes

Preterm infants have higher rates of...

Functional, growth, developmental disorders

Risk factors for preterm labor

- Idiopathic

- SES

- Prior OB complications

- Current complications (chronic diseases, acute infections, surgical / anatomic)

S/S & PE of preterm labor

- Uterine contractions

- Dilation & defacement of cervix — Change of at least 1 cm OR well-effaced & at least 2 cm

- Bloody show, mucus plug, vaginal bleeding

Diagnostic workup / eval of preterm labor

- Determine GA

- Continuous fetal monitoring & tocodynamometry

- UA (straight cath)

- Cervical cultures — GC, chlamydia

- BV wet mount

- Group B strep cultures

- Cervicovaginal swab for fetal fibronectin — Negative → Low risk of imminent delivery within 2 weeks

Indications for amniocentesis for preterm labor evalulation

EGA unclear — Assess signs of fetal lung maturity

Management of preterm labor between 24 & 33 6/7 weeks

- Corticosteroids — Accelerates fetal lung maturity; Can repeat if lasts 7 days & GA still <34 weeks

- Tocolytic therapy (terbutaline & nifedipine MC) — Slow/delays labor (short-term use 48h) to allow administration of steroids & magnesium sulfate; Successful if <4-6 contractions/hour W/O further cervical change

- ABX (PCN or ampicillin 1st line) — Positive / unknown group B

- Magnesium sulfate — Reduce risk of CP if GA 23-32 weeks

1st line tocolytic therapy for GA <32 weeks

Indomethacin

When should tocolytic therapy be considered?

Cervical dilation <5 cm in acute preterm labor

Management of delivery of preterm infant

- Hospital with NICU — Postbirth transfer is risky

- Obtain cord blood pH & blood gas

ADRs of tocolytics: Beta-mimetrics (terbutaline) (maternal & fetal)

Maternal: Pulm edema, hypotension, tachycardia, hyperglycemia, hypoK+

Fetal: Tachycardia, hyper/o-glycemia, ileus

ADRs of tocolytics: Nifedipine (maternal & fetal)

Maternal: Hypotension, tachycardia, HA, dizziness, flushing

Fetal: Tachycardia, hypotension

ADRs of tocolytics: Indomethacin (maternal & fetal)

Maternal: Heartburn, GI bleeding, coag abnormalities, thrombocytopenia, renal failure, hepatitis, worsened HTN

Fetal: Renal dysfunction, pulm HTN, oligohydramnios, postpartum PDA, premature closure of ductus arteriosus, increased risk for necrotizing enterocolitis & inter ventricular hemorrhage

**DO NOT administer after 32 weeks

ADRs of tocolytics: Magnesium sulfate (maternal & fetal)

Maternal: Diplopia, SOB, pulm edema, chest pain, muscle weakness, tetany, hypotension, resp depression, flushing

Fetal: Lethargy, hypotonia, resp depression

Indications for interventions for prevention of preterm labor

- Prior preterm birth — Progesterone (IM or vaginal)

- Short cervix on TVUS — Vaginal progesterone

Management of preterm labor for 20-22 weeks GA

- Able to sustain pregnancy for more weeks → Improved viability BUT significant risk of mobility

- Bedrest, tocolysis also carries risks

**NOT considered viable

Management of preterm labor for 34037 weeks GA

- Corticosteroids — Reduces respiratory morbidity

- Otherwise, allow delivery; Survival rate is identical to 37+ weeks

Maternal factors where preterm labor should NOT be suppressed

- Severe HTN

- Pulm / cardiac disease

- Advanced cervical dilation >4cm

- Maternal hemorrhage

Fetal factors where preterm labor should NOT be suppressed

- Fetal death / lethal anomaly

- Intrauterine infection

- Fetal distress

- Est fetal weight ≥2500 g

- Severe intrauterine growth retardation