Prof. M.C.BansalMBBS., MS., FICOG., MICOG.Founder Principal & Controller,Jhalawar Medical College & Hospital Jjalawar.MGMC & Hospital , sitapura ., Jaipur

ANTEPARTUM FETALMONITERING

ANTEPARTUM FETAL MONITORING

Two thirds of fetal deaths occur before the onset of labor, many of which are due to uteroplacental insufficiency.

No single test can detect abn with 100% accuracy

Ideal detection: allows intervention before fetal death or damage from asphyxia.

Preferable: treat disease process and allow fetus to go to term.

DRAWBACK- false positive / negative results may cause undue intervention and lead to premature iatrogenic delivery or fetal compromise.

• Assessment of Uterine growth

• Fetal movement counting

• Non stress test- indicator of fetal health.

• Contraction stress test – indicator of U.P func.

• Fetal Biophysical profile

• Modified Biophysical profile

• Doppler velocimetry

• Percutaneous umbilical blood sampling

METHODS OF ASSESSMENT

Occurs due to inadequate delivery of nutritive & respiratory substt to fetal tissues.

Can be due to:-

UTEROPLACENTAL INSUFFICIENCY (UPI)

Inadequate exchange within placenta due to-

1. increased thickness2. reduced blood flow3. decreased sf area

Maternal inadequacy to deliver nutrients & oxygen through placenta

Fetal uptake problems

SEQUENCE OF FETAL DETERIORATION/COMPROMISE

Generalized Fetal Well Being with some Nutritional Compromise

Fetal Growth Retardation with Marginal Placental Dysfunction

Fetal Hypoxia under Stress cond. with Decreasing Respiratory Function

Asphyxia/Death/Residual effects with Profound Respiratory Compromise

MATERNAL RISK FACTORS OF UPI

1.PRE-ECLAMPSIA , CHRONIC HYPERTENSION2.COLLAGEN VASCULAR DISEASES3.DIABETES MELLITUS4.RENAL DISORDERS5.BLOOD- MATERNAL ANAEMIA, RH

SENSITISATION6.HYPERTHYROIDISM7.THROMBOPHELIA8.CYANOTIC HEART DISEASE9.POST DATED PREGNANCY10.FETAL GROWTH RESTRICTION

UTERINE GROWTH ASSESSMENT

General rule: Fundal height in centimeters = weeks of gestation (2nd trim.)

Johnson’s formula = [Ht. of uterus above symphysis (cm) – 12 (vx at or above ischial spines) OR 11 (vx below ischial spines)] x 155

Exceptions: Maternal Obesity, Multiple Gestation, Polyhydramnios, Abnormal Fetal Lie, Oligohydramnios, Low Fetal Station, and Fetal Growth Restriction.

Abnormalities of fundal height should lead to further investigation.

Accuracy: poor

FETAL MOVEMENT COUNTING

MATERNAL PERCEPTION OF REDUCTION IN MOVEMENTS MAY BE A RED FLAG SIGN TO IMPENDING FETAL DISTRESS.

•4 fetal behaviour states as described by Nijhuis & colleagues (1982) based on fetal movements, fetal heart rate & eye movements :-

1. State 1F- Quiescent state- quiet sleep with narrow oscillatory bandwidth of fetal heart rate.

2. State 2F- Frequent gross body movements, cont. eye movements, wider oscillations of fetal heart rate. (=REM of neonate)

3. State 3F- Continuous eye movements in absence of body movements and heart rate accelerations. The existence of such state is doubtful

4. State 4F- Vigorous body movements with constt eye movements and heart rate accelerations.

USG observations show that fetus has gross body movements approx 10% of the time and as many as 30 movements can occur in an hour.

Most commonly used method is “ COUNT TO 10” (Moore et all 1989) [Am J Obs-Gyn]

Patients are instructed to count until they reach 10 movements.

If such 10 movements are noticed in 10 hours, most probably the fetus is in good health. (1 movement in each hour).

If mother reports <10 movements in 10 hours OR there is doubling of hours usually required to complete 10 movements, she should be subjected to further evaluation.

• Studies have indicated a good correlation b/w fetal movements perceived by the mother and those picked on a real time scan.

• Periods of fetal activity lasts for about 40 mins and that of rest about 20 mins. The mother usually perceives 70-80% of these movements.

• Passive fetal movements begin by about 7wks and become more coordinated towards end of pregnancy. (Vindla and James 1995)

• Beyond 8 wks, body movements are never absent for periods exceeding 13 minutes. (De Vries and co worker's 1985)

•Between 20-30 wks, general body movements become organised and fetus starts to show ‘rest-activity cycles’. (Sorokin and co-workers 1982)

FACTORS AFFECTING PERCEPTION OF MOVEMENTS

Maternal obesity

Excessive liquor

Placental site (?)

Fetal malformations

NON STRESS TESToMost commonly used test. The patient placed in semi fowler’s position.

oNon invasive, easy to perform, interpret and readily accepted by patients.

oTest looks for presence of fetal heart rate (FHR) accelerations associated with fetal movements.

oThis reflex involves the cerebral cortex, and is affected by physiological (fetal sleep) or pathological influences (fetal hypoxia) on fetal brain.

•Two normal patterns of NST are:-

a. Reactive - 2/more accelerations of FHR of min 15 beats/min, lasting for atleast 15 secs from baseline to baseline within 20 mins obsv pd, associated with fetal movements (as perceived by the mother).

b. Non Reactive- Lack of such accelerations for a pd of 40 mins. (20 mins as per normal obsv pd +

additional 20 mins)

VIBROACOUSTIC STIMULATION Introduced by Zimmer et all, 1993.

Stimulation via an artificial larynx, over the fetal head along with NST attached & producing vibratory acoustic stimulus of approx 80Hz and 82dB.

A healthy fetus responds with a sudden movement (Startle Response) followed by FHR acceleration.

Response to VAS is gestational age dependant, viz, a fetus of less than 24 wks doesn’t respond to it.

Between :-24-27wks 30% 27-30wks 86% fetuses will respond to the stimulus. >31wks 90%

NST is to be read keeping in account all the variables namely, 1. Baseline FHR 2. Variability of FHR 3. Presence /absence of decelerations 4. Presence /absence of accelerations each one being separately analysed.

Normal baseline FHR IS 110-160 bpm. >160 is tachycardia & <110 is bradycardia.

Variability is the most imp parameter to be read and interpreted. It depends upon interactions of fetal sympathetic & parasympathetic nervous systems. It’s influenced by gestational age, fetal tachycardia, maternal medications, congenital anomalies and fetal acidosis.

A non reactive NST in presence of variability suggests a false positive reading

•Can’t pick up early fetal compromise. Though, this concern hasn’t been proven in clinical trials and hasn’t effected the use of NST as a primary tool for diagnosis.

•Use of test alone without realising the significance of other tests which may be better for the given patient. Eg. In postdated pregnancies, simultn assessment of amniotic fluid volume is necessary.(Kontopoulos and Vintzileos, 2004)

•Gandhi (2003), emphasised that though false positive rate ranges between 65-70%.

•A cumulative view of 50,000 cases (Ware and Devoe, 1994) revealed a perinatal mortality of 6.2/1000.He also states that diagnostic value of NST remains as good as CST and is simpler to perform.

drawbacks

Devoe, L, Glob. libr. women's med.,(ISSN: 1756-2228) 2008; DOI 10.3843/GLOWM.10210

CONTRACTION STRESS TEST

Based on experimental evidence showing that uteroplacental blood flow decreases markedly or ceases during each uterine contraction. Thus, uterine contractions cause a hypoxic state that a normal, healthy fetus can tolerate without difficulty.

In contrast, fetus with acute/chronic problems will not be able to tolerate such a decrease in oxygen supply & will demonstrate decelerations of FHR following contraction.

Contractions can be- a. spontaneously occuring b. induced with oxytocin drip ( predictable response) c. nipple stimulation (unpredictable response)

HOW TO PERFORM CST1. Patient on semi fowler’s position.

2. Tocographic equipment applied to maternal abdomen, observe uterine activity with FHR variations every 15-20 mins.

Spontaneous contractions present in many cases. If not induction of contractions may be necessitated.

3. Start IV oxytocin at 0.5 mU/minute, using pump. Double the rate every 15-20 mins till 3 contractions, of 40-60 secs occur within 10 mins time. Amount required to achieve adequate contractions usually below 16 mU/ml.

Alternately, warm towel can be used to stimulate the nipples.

4. After completion uterine contractions and FHR should be monitered till they return to baseline. If not, subcutn admin of 250 mg of terbutaline reqd to paralyze the uterus.

End point of CST is presence or absence of decelerations of FHR with uterine contractions.Late decelerations are one of the earliest indicators of fetal compromise & appear due to loss of variability, decreased movement, loss of tone.

The test is infrequently used due to:- 1. long obsv periods by trained professionals. 2. risks and contraindications.

*Positive: presence of late decelerations with at least 50% of the contractions

*Negative: no late or significant variable decelerations

*Equivocal—Suspicious: presence of late decelerations with fewer than 50% of contractions) or significant variable decelerations

*Equivocal—Tachysystole: Presence of contractions that occur more frequently than every 2 minutes or last longer than 90 seconds in the presence of late decelerations

*Equivocal—Unsatisfactory: Fewer than three contractions occur within 10 minutes, or a tracing quality that cannot be interpreted

CONTRAINDICATIONS1. Placenta praevia

2. Prior classical cesarean section

3. Prior extensive uterine surgery

4. Preterm labour / High risk of preterm labour

5. PROM

6. Incompetent os

A. Negative CST. Absence of late decelerations, often occasional accelerations.

 B. Positive CST. Recurrent uniform late decelerations present. 

C. CST. Variable decelerations present. 

D. Hyperstimulation. Prolonged contraction with reflexive deceleration.

Positive CST conveys the strong possibility that placental respiratory insufficiency is present, although it does not indicate the probable duration or progress of this condition.  In addition, the positive CST conveys much higher risk of fetal distress, low 5-minute Apgar scores, and IUGR than does a negative test.

Devoe, L, Glob. libr. women's med.,(ISSN: 1756-2228) 2008; DOI 10.3843/GLOWM.10210

Combines NST with ultrasound assessment of 4 variables.

5 parameters are-•Fetal Breathing Movements- 30 secs sustained movmnt in 30 mins obsv.

•Fetal Movement- 3/more gross body movements in 30 mins obsv

•Fetal Tone- 1/ more movement from flexion to extension and return to flexion.

•FHR reactivity- 2/more accelerations of 15bpm, lasting atleast 15 secs.

•Fluid Volume- at least 2 pockets meas. 2cm in 2 perpendicular planes.

Variables are dependant on integrity of fetal CNS & are affected in fetal compromise.

Each parameter assigned points-- 2 if present/normal. 0 if absent/abnormal.

A BPP normally is not performed before the second half of a pregnancy, since fetal breathing movements do not occur in the first half.

A BPP of 8 or 10 is generally considered reassuring, as long as score of 8 doesn’t include abnormal fluid volume.

PRESENCE OF OLIGOHYDRAMNIOS DEMANDS FURTHER TESTING NO MATTER WHAT THE SCORE IS.

A score of 6 is Equivocal and requires further testing to verify findings.

A score of 4/less suggests fetal compromise.

BPP variables are dependant on fetal CNS development acc to gestational age.

Fetal tone & movement appear b/w 7-9 wks and require activity of brain cortex.

Fetal breathing movements begin at 20-21 wks & depend on centres on ventral surface of 4th ventricle.

FHR reactivity appears b/w 28-30 wks & controlled by post hypothalamus, upper medulla.

Sensitivity of each centre to hypoxia is different & ones which develop earlier are more resistant to effects of fetal hypoxia.

First manifestation of fetal acidosis- nonreactive NST, lack of fetal breathing movements. Decreased body movements and loss of tone occur with severe compromise.

MODIFIED BPPVintzileos et al (1987) , Clark et al (1989), Miller et al (1996)

Excellent test for primary fetal surveillance.

Combines use of NST with VAS, and Amniotic Fluid Index

Test has:- excellent positive & negative predictive values easy to interpret clearly defined end points average time needed is 20 mins

Following guidelines are useful while reading the results:-

1. Both NST and AFI are normal, cont weekly fetal monitoring.

2. Both tests abnormal; a) >36 wks, best option is delivery b) <36 wks, individualized treatment

3. NST reactive, but AFI low, search for causes of UPI or undiagnosed ROM.

4. AFI normal, but NST non reactive, further testing with Doppler, CST, BPP.

FETAL DOPPLER*Non invasive technique to assess placental blood flow to the fetus.

*Uses waveforms to describe Systolic (S) & Diastolic (D) blood flow through vessels.

S

D

*Three commonly used ratios are:- a. S/D Ratio b. S-D/S = Resistance Index c. S-D/Mean = Pulsatility Index

Acc to Trudinger (2007);

>40% of total fetal ventricular output directed to placenta

obliteration of utero placental circulation

increases afterload

further hypoxia

dilatation & redistribution of MCA blood flow

pressure rises in Ductus Venosus due to

increased afterload to right side of fetal heart

UMBILICAL ARTERY DOPPLER•Vessel normally has forward flow throughout cardiac cycle & diastolic flow increases as gestation advances.

•So, S/D ratio decreases as gestation advances, from 4 at 20 wks to <3 by 30 wks & finally 2 at term.

•S/D ratio is taken as abnormal if it’s above 95th percentile for gestational age OR diastolic flow is absent or reversed.

•A resistance index > 0.72 is greater than the normal limits from 26 weeks gestation onwards.

• Abnormal waveforms can be present for weeks before there is evidence of fetal compromise. These are a marker of a high risk situation and should not normally be used in isolation as an indication for delivery.

•Most would consider delivering a fetus with absent end-diastolic velocity from about thirty two weeks gestation following administration of corticosteroids.

•However, reversal of end diastolic blood flow is an ominous sign & predicts severe fetal compromise, possible death, requiring urgent delivery of the viable fetus.

MIDDLE CEREBRAL ARTERYKonjoe & colleagues (2001) [Br J of Obs & Gyn]Doppler studies of MCA showed, hypoxic fetii attempt brain sparing by reducing cerebrovascular impedance & thus reducing blood flow. In growth restricted fetii this effect shows reversal.

The effect however, isn’t protective, rather indicates negatively on the fetal health.

NORMAL doppler flow

INCREASED DIASTOLIC FLOW, due to reduced resistance.

Highly reduced resistance, shown by FURTHER INCREASE OF DIASTOLIC FLOW.

REVERSAL OF DIASTOLIC FLOW, indicative of severe fetal compromise.

CORDOCENTESIS

•F. Daffos (1983-1985)•22 G / Finer needle needed. •Can be performed at any site on umbilical cord, but placental insertion preferred.•One should avoid piercing through the placenta.

INDICATIONS

a) Rapid Karyotype In Fetuses Detected With Anomalies On USG.

b) Fetal Hemolytic Disease

c) Suspected Fetal Viral Infection

d) Non Immunologic Hydrops Fetalis

e) Suspected Fetal Thrombocytopenia

f) Twin To Twin Transfusion

g) Fetal Heamoglobinopathies

RISKSBLEEDING FROM PUNCTURE SITE

VASO VAGAL REFLEX

FETAL BRADYCARDIA

Ideally an obstetrician should adequately inform the patient of all the pros and cons of any test method being employed, and the efficacy and limitations of the same.

In many instances, failing to do so, may cause the patient to have unreasonable expectations which when unfulfilled may lead to animosity and disappointment towards the doctor and cause medico-legal problems

REMARK

SOURCES1. WILLIAMS TEXTBOOK OF OBSTETRICS 23RD EDITION.

2. PRACTICAL BOOK TO HIGH RISK PREGNANCY 3RD EDITION by FERNANDO ARIAS.