This was originally developed in Singapore,
in a hospital with 25,000 deliveries per year with
28 high risk and 18 low risk rooms staffed by 4 trained
and 4 axillary staff. As a consequence there was little
time for adequate auscultation and the intrapartum
asphyxia rate was high. The hypothesis behind the admission
CTG was that a reactive trace with accelerations would
be predictive of a baby at low risk of intrapartum
asphyxia whereas a non reactive, suspicious or pathological
trace would need either more intense monitoring or
expedited delivery. For those with a reactive trace,
any slowly developing compromise would be accompanied
with a rise in baseline which could be detected by
auscultation and acute bradycardias would usually be
accompanied with an acute event or take place in late
first or early second stage.
The original research examined a low risk population.
The test was applied to 130 women in labour with pH
determinants in scalp blood and cord blood at birth
( 1).
Only 0.9% of those with a reactive test had intrauterine
asphyxia in labour as compared to half of those with
ominous traces. The test was then used as a screening
test in 1041 women with similar results.
Two subsequent studies have examined high risk pregnancies,
which by current definitions should have continuous
intrapartum monitoring (2),3).
The one randomised controlled trial of admission CTG
vs Doppler auscultation in a population of 3751 women
with no pre identified risk factors showed no significant
difference in metabolic acidosis or any other measure
of neonatal outcome (4).
The NICE guidelines concluded that current evidence
does not support the admission CTG in a low risk pregnancy
and it is therefore not recommended (5).
They list risk factors to distinguish between high
and low risk. However, whilst the maternal conditions
are usually evident, the fetal complication of growth
restriction is currently poorly detected. Only 26%
of small for gestational age babies were detected as
small before birth in an unselected hospital population
(6).
This was even less in a low risk population (7).
In addition the complications of oligohydramnios and
abnormal uterine artery Dopplers will only have been
detected if there has been previous suspicion of growth
restriction and therefore an ultrasound scan to investigate
this. If these women are then subject to intermittent
auscultation only, as current evidence suggests is
appropriate for truly low risk pregnancy, there is
a risk that fetal heart abnormalities of reduced baseline
variability and shallow decelerations representing
chronic in utero compromise may be missed.
References
1.Ingemarsson I, Arulkumaran S, Ingemarrson E, Tambyraja
RL, Ratnam SS. Admission test: a screening test for
fetal distress in labour. Obstet Gynecol 1986; 68:
800.
2. Umstat MP. The predictive value of abnormal fetal
heart rate patterns in early labour. Aust N Z J Obstet
Gynaecol 1993; 33: 145-9.
3. Kulkarni AA, Shotri AN. Admission test: a predictive
test for fetal distress in high risk labour. J Obstet
Gynaecol Res 1998; 24: 255-9.
4. Mires G, Williams F, Howie P. Randomised controlled
trial of cardiotocography versus Doppler auscultation
of fetal heart at admission in labour in low risk obstetric
population. BMJ 2001; 322: 1435-1498.
5. The Use Of Electronic Fetal Monitoring: The use
and interpretation of cardiotocography in intrapartum
fetal surveillance. Evidence-based Clinical Guideline
Number 8. RCOG Press.
6. Hepburn M, Rosenberg K. An audit of the detection
and management of small for gestational age babies.
Br J Obstet Gynecol 1986;93: 212-216
7. Kean LH, Liu DT. Antenatal care as a screening
tool for the detection of small for gestational; age
babies in the low risk population. J Obstet Gynaecol
1996; 16:77-82.
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