ANTEPARTUM FETAL SURVILLANCE

Dr.Nourah Al Qahtani Consultant OB/GyneMaternity Hospital

King Saud Medical City

Introduction: The goal of antepartum fetal

assessment1. Identify fetuses at risk of intrauterine death or other complications of intrauterine asphyxia2.Intervene to prevent these adverse outcomes.

The main techniques for fetal assessment.1.Nonstress test 2.Biophysical profile 3.Modified biophysical profile 4.Contraction stress test5.Fetal movement count

PHYSIOLOGICAL BASIS FOR FETAL TESTING 1.Antepartum testing is based on the fetus responds to hypoxemia with a detectable

sequence of biophysical changes, beginning with signs of physiological adaptation and potentially ending with sign of physiological decompensation .

2.Fetal biophysical parameters can be affected by factors unrelated to hypoxemia, such as gestational age, maternal medication/smoking, fetal sleep-wake cycles, and fetal disease/ anomalies

EFFICACY – ability to improve pregnancy outcome has not been evaluated by large, well designed randomized trails

INDICATION FOR FETAL SURVEILLANCE1.Diabetes 2.Hypertensive disorder 3.Fetal growth restriction 4.Twin pregnancy 5.Post term pregnancy6.Decreased fetal activity 7.Systemic lupus erythematosus 8.Antiphospholipid syndrome9.Sickle cell disease 10.Isoimmunization11.Oligohydramnios or polyhydramnios 12.Prior fetal demise13.Preterm premature rupture of membranes 14.Other – nonimmune hydrops, maternal vascular disease, poorly controlled maternal hyperthyroidism and maternal vascular disease are associated with an increased risk of fetal demise and generally considered appropriate indication for antenantal fetal testing.

1.Fetal Movement counting – objective maternal assessment of fetal movements is based on evidence that fetal movement decreases in response to hypoxemia

2.Contarction stress test – is based on the fetal response to a transient reduction in fetal oxygen delivery during uterine contractions. The fetus becomes hypoxemic (fetal arterial pO2 below 20mm Hg), fetal chemoreceptor and borereceptors, as well as sympathetic and parasympathetic influences, respond by reflex slowing of the fetal heart rate (FHR), which may manifest clinically as late decelerations.

3. Nonstress test – FHR accelerations, spontaneous or provoked (e,g by vibroacoustic stimulation), have been shown to be a good indicator of normal fetal autonomic function and absence of acidosis and neurologic depression.

The main advantage of the NST over the CST is that it does not require an intravenous line oxytocin, or contractions. Disadvantages are that the false – negative and false- positive rates are higher than for the CST (a false – negative NST is when an antepartum stillbirth occurs within one week of a reactive test, a false- positive NST is nonreactive test that is followed by a normal back-up test, such as a negative CST or high biophysical profile score)

4. Biophysical profile - the biophysical profile (BPP) combines the NST with ultrasonographic fetal assessment by assigning points to the following parameters:

1. Amniotic fluid volume (AFV)2. Fetal breathing movements 3. Fetal body movements 4. Reflex/tone/flexion-extension movement.

Criteria for the biophysical profile test

Nonstress test: 2 points if reactive, defined as at least 2 episodes of FHR accelerations of at least 15 bpm and at least 15 seconds duration from onset to return associated with fetal movement within a 30-minute observation period.

Fetal breathing movements: 2 points if one or more episodes of rhythmic breathing movements of ≥30 seconds within a 30-minute observation period.

Fetal tone: 2 points if one or more episodes of extension of a fetal extremity or fetal spine with return to flexion.

Amniotic fluid volume: 2 points if a single pocket of fluid is present measuring at least 2 cm by 1 cm. However, some clinicians use other criteria such as the amniotic fluid index.

Fetal movement: 2 points if three or more discrete body or limb movements within 30 minutes of observation. An episode of active continuous movement is counted as one movement.

The BPP score has a direct linear correlation with fetal pH the modified biophysical profile (mBPP) consists of the NST as a measure of acute oxygenation and assessment of AFV as a measure of longer- term oxygenation.

The false-negative rates for the BPP and mBPP are very low, but the false- positive rates are high (a false – negative BPP or mBPP is when an antepartum stillbirth occurs within one week of a high score, a false positive is a low score that is followed by a normal back – up test.

5.Amniotic fluid volume – in the hypoxemic fetus, cardiac output is redirected to the brain, heart, and adrenals and away from less vital organs, such as the kidney, the reduction in renal perfusion leads to decreased fetal urine production, which may result in decreased amniotic fluid volume (oligohydramnious) over time.

Sonographic determination of the single deepest amniotic fluid pocket (SDP) is the preferred method of AFV assessment. The SDP and the amniotic fluid index (AFI) method are equivalent in their prediction of adverse outcome in singleton pregnancies, but use of the AFI increases the number of labor inductions and caesarean deliveries without any improvement in perinatal outcome.

6. Doppler velocimetry – provides information about utroplacental blood flow and fetal responses to physiological challenges.

1.doppler indices from the umbilical artery increase when 60 to 70 percent of the placental vascular tree is compromised.

2. fetal middle cerebral artery impedance falls.

3. fetal aortic resistance rises to preferentially direct blood to fetal brain and heart.

4. end diastolic flow in the umbilical artery ceases or reverses and resistance increases in the fetal venous system (ductus venosus,inferior vena cava). Umbilical artery Doppler is the most common Doppler technique used for fetal assessment where fetal hypoxema is a concern. Fetal middle cerebral artery – peak systolic velocity is the best tool for predicting fetal anemia in at-risk pregnancies.

1. Umbilical artery - most useful for monitoring fetuses with early-onset growth restriction due to uteroplacental insufficiency. Umbilical artery flow velocity waveforms of normally growing fetuses are characterized by high- velocity diastolic flow, whereas in growth-restricted fetuses, umbilical artery diastolic flow is diminished, absent, or even reversed in severe cases. In the growth – restricted fetus absent or reversed end diastolic flow is associated with fetal hypoxemia and academia, and increased perinatal morbidity and mortality

►The American college of obstetrics and gynecologist (ACOG) practice guidelines

support the use of umbilical artery Doppler assessment in the management of suspected

intra uterine growth restriction, but not for normally grown fetuses.

2. Middle cerebral artery - the best tool for monitoring for fetal anemia ssuch as those affected by rhesus alloimmunization

3. Fetal veins — Doppler evaluation of fetal veins combined with umbilical artery assessment may be useful for predicting outcomes in growth-restricted fetuses . The fetal precordial veins (ductus venosus and inferior vena cava) and the umbilical vein are the vessels most commonly evaluated in clinical practice,

4. Uterine artery 

1.Impedance to flow in the uterine arteries normally decreases as pregnancy progresses.

2.Failure of adequate trophoblast invasion and remodeling of maternal spiral arteries is characterized by a persistent high-pressure uterine circulation and increased impedance to uterine artery blood flow.

3. Elevated resistance indices and/or persistent uterine artery notching at 22 to 24 weeks of

gestation indicate reduced blood flow in the maternal compartment of the placenta and have

been associated with development of preeclampsia, fetal growth restriction, and perinatal death.

CHOICE OF TEST — The choice depends on multiple factors:1.gestational age (up to 50 percent of NSTs are not reactive in healthy 24 to 28 weeks fetuses 2.availability, 3.desire for fetal biometry or follow-up of a congenital anomaly, 4.ability to monitor the fetal heart rate (eg, the NST and CST may not be interpretable in a fetus with an arrhythmia), 5. cost.

TIMING — Testing should begin as soon as an increased risk of fetal demise is identified and delivery for perinatal benefit would be considered if test results are abnormal.

●DURATION AND FREQUENCY 1.Fetal testing should be performed periodically until delivery if the clinical condition that prompted fetal surveillance continues to exist.

2.A single normal test result is adequate if performed for a nonrecurring indication in an otherwise low-risk pregnancy (eg, reactive nonstress test after a minor motor vehicle accident and no signs of labor or vaginal bleeding).

3.Testing is typically performed weekly, but the frequency is generally increased if there is a change in pregnancy status (eg, fetal growth percentile falls from 10th percentile to 3rd percentile, worsening preeclampsia) or in clinical settings considered to be very high risk (eg, fetal growth restriction with absent or reversed diastolic flow)

4.There are no data from randomized trials on which to base recommendations for the optimum frequency of fetal monitoring (daily, every other day, twice per week, once per week).

5.These decisions are based on expert opinion, clinical experience with similar high-risk pregnancies, and community standards.

 

●MANAGEMENT OF ABNORMAL TEST RESULTS.

1.Given the high rate of false-positive tests, an abnormal test result is generally followed by additional testing with a different test (eg,

contraction stress test [CST] or biophysical profile [BPP] after a nonreactive nonstress test [NST]) to provide more information about fetal status.

2.The clinical setting to be considered: (A.)If a temporary maternal condition, such as diabetic

ketoacidosis or acute bronchospasm, may account for the abnormal test result, prompt treatment of the maternal condition may also improve fetal oxygenation and lead to a normal test result on subsequent testing.

(B.)In chronic conditions, clinical judgment guides management, taking into account factors such as gestational age (low threshold for delivery for an abnormal test result at term), severity of disease (eg,

diabetes with poor glycemic control versus good glycemic control), progression of disease (eg, fetal growth falls from the 10th percentile to the 3rd percentile), and other available information (eg, decelerations, absent variability, or bradycardia on a nonreactive NST; BPP score 0 versus 4 or 6; absence of accelerations on a positive CST).

*After a positive CST, up to 40 percent of fetuses have been reported to tolerate labor without FHR changes necessitating intervention.

   

Late decelerations

Late decelerations are characterized by a gradual decrease and return to baseline of the fetal heart rate associated with uterine contractions. The deceleration is delayed in timing, with the nadir of the deceleration occurring after the peak of the contraction. The onset, nadir, and recovery usually occur after the onset, peak, and termination of a contraction. In this example, variability is minimal.