Routine induction of labour at 41 weeks gestation:
nonsensus consensus
BJOG: An International Journal of Obstetrics
and Gynaecology Vol: 109 Issue: 5pp: 485-491 PII:
S1470032802010042. Copyright © 2002 RCOG
All rights reserved. To order it online, go here.
Savas M. Menticoglou, Philip F. HallDepartment
of Obstetrics, Gynaecology and Reproductive Sciences,
University of Manitoba, Winnipeg , Canada. Accepted
16 2002
Article Outline:
1. Introduction
2. What are the true fetal and neonatal risks
of reaching 41 weeks of gestation?
3. What are the maternal risks of reaching 41
weeks of gestation?
4. Resource consequences of a policy of routine
induction at 41 weeks of gestation
5. Inevitable, unintended and undesirable consequences
of routine induction at 41 weeks
6. Conclusion
References
* * * * *
"Falsehood flies and the truth comes limping
after; so that when men come to be undeceived
it is too late: the jest is over and the tale
has had its effect." Jonathan Swift,
The Examiner, No. 15, November 9, 1710
1. Introduction
Traditionally pregnancy has been considered 'post-term'
at 42 completed weeks of gestation. At this gestation,
if the cervix is unfavourable, debate over best
practice has been between routine induction of
labour and expectant management with some form
of serial fetal monitoring.
Popular wisdom seems to be that meta-analysis
of the available randomised controlled trials
has settled the question in favour of routine
induction[ 1 ]. The largest included trial, containing
over half the cases ( n = 3407), was carried out
in Canada and published in 1992[ 2 ]. The results
of the meta-analysis led the Society of Obstetricians
and Gynaecologists of Canada (SOGC) to issue Clinical
Practice Guidelines in 1997[ 3 ]. The guidelines
recommended that:
- after 41 completed weeks of gestation, if
the dates are certain, women should be offered
elective delivery;
- if the cervix is unfavourable, ripening should
be undertaken; and
- if expectant management is chosen, assessment
of fetal health should be initiated.
It is presumed that randomised controlled trials
or, even better, meta-analyses of randomised trials,
provide the best evidence to determine appropriate
care. However, once information has been declared
'the best available evidence', particularly if
that assertion is used to justify clinical practice
guidelines or 'consensus', further inquiry may
be inhibited[ 4 ].
Since it is implied that 'the answers are all
in', mutation from clinical practice guideline
to standard of care is prompt and uncomplicated,
particularly if the labels 'consensus' or 'policy
statement' are used between the two as conceptual
mutagens. The standard of care in Canada now is
assumed to be routine induction at 41 weeks. This
commentary is intended to give pause to those
who have accepted and adopted this standard.
2. What are the true fetal and neonatal risks
of reaching 41 weeks of gestation?
The SOGC Clinical Practice Guidelines assert
that "women who reach 41 weeks should be
counselled appropriately regarding the higher
risk...to their babies if they should pursue a
policy of expectant management"[ 3 ]. How
large is this purported higher risk, and what
is the strength of evidence used to support this
assertion?
The following information comes from studies
conducted before 1992 when '41 weeks undelivered'
had not been categorised as vigorously as a time
of higher risk. In that era, intervention by induction
for gestation only was not routine practice, and
fetal surveillance because the pregnancy was undelivered
at 41 weeks of gestation was not used.
Such evidence does not describe the natural history
of all pregnancies that would have reached 41
weeks without intervention. Women with identified
maternal or fetal complications such as pregnancy-induced
hypertension, other medical problems, or suspected
fetal growth restriction likely would have been
delivered sooner, and women with favourable cervices
might have been induced, but the situation of
the remainder would have been similar to that
of women eligible for the Canadian study.
Based on data from New York City (1987-1989)[
5 ], Japan (1989-1992)[ 6 ], Sweden (1982-1991)[
7 ], and London (1989-1991)[ 8 ], the risk of
stillbirth in the subsequent week to women undelivered
at the beginning of their 41st week (41 weeks
zero days) is about 0.1% (1.04-1.27 per 1000)
- (Table: [ 1]. Similar estimates were presented
in reports from New Zealand (1983-1986)[ 9 ] and
England (1978-1985)[ 10 ]. The stillbirth rate
in the expectant arm of the Canadian study was
similar at two fetal deaths in 1700 women (1.18
per 1000)[ 2 ].
Table 1: Stillbirth risk in following week per
1000 undelivered women at beginning of week. (6.49
KB) [unavailable]
These estimates are contemporary with the Canadian
trial and are consistent, as they are with the
situation contemporary to the Canadian study at
one Winnipeg tertiary obstetric hospital - (Table:
[ 2]. In the latter setting, from 1982-1991, induction
for gestation only was not routine and fetal surveillance
for post-term pregnancy was not begun until 42
weeks. Of 7725 pregnancies that reached 41 weeks
undelivered, eight stillbirths occurred in the
next week, and there were three neonatal deaths-
two from disseminated herpes, one from birth asphyxia-
in babies born between 41 weeks zero days and
41 weeks six days.
Table 2: Women's Hospital, Winnipeg 1982-1991.
Exclusions:
1) Transferred from other institution with fetus
already dead in utero;
2) No prenatal care before gravida arriving
with dead fetus;
3) Fetus known to have died before 36 weeks;
4) Principal cause of death related to congenital
anomaly. (8.85 KB)
The authors of the Canadian study suggested that,
were it not for their fetal monitoring, perinatal
mortality would have been higher than two babies
in 1700 (1.18 per 1000).
However, evidence from six countries (one being
Canada) suggests that, as of a decade ago, when
such monitoring was not done for gestation alone,
the stillbirth rate in the subsequent week was
about one in 1000 and approximately 1000 inductions
would have been necessary at 41 weeks to prevent
one stillbirth in the ensuing week, presuming
cause and effect relationship between that death
and gestational age.
Since serial fetal assessment is now common
in our setting, in part in defence against implications
of the SOGC Clinical Practice Guidelines, most
significant perinatal complications have been
identified and dealt with by delivery before 41
weeks, and the odds of stillbirth in the following
week likely have been further reduced.
What of the meta-analysis[ 1 ] which claims to
demonstrate that "routine induction of labour
after 41 weeks reduces perinatal death"?
Meta-analysis attempts to describe what happened,
but not why. As retrospective assessment, inevitably
such efforts are subject not only to what happened
in the past, but also to the accuracy and completeness
with which those events have been described and
analysed.
According to the aggregate data, seven nonanomalous
perinatal deaths occurred in 3002 women randomised
to expectant management, compared with 1 from
3071 women who were induced. Of the seven perinatal
deaths in the expectant arms, two deaths occurred
in the 1960s[ 11 ], before the availability of
modern fetal testing.
Of those, one was a stillbirth in a mother with
an abnormal glucose tolerance test; such a situation
would not likely be allowed to reach 41 weeks
now, and was a specific exclusion from the Canadian
study.
The other was a neonatal death, from meconium
aspiration, following refusal of induction by
the mother after positive amnioscopy.
One perinatal death[ 12 ], in China, was caused
by pneumonia in the newborn period, a cause unrelated
to the duration of pregnancy.
One perinatal death[ 13 ] was caused by meconium
aspiration in a baby born at 43+3 weeks, which
is irrelevant to whether induction should be carried
out at 41 weeks.
Of the two deaths in the Canadian trial[ 2 ],
one was a stillbirth at 41+5 weeks, but the mother
had not received any fetal testing.
The second was an intrapartum death of a 2600
gm infant at 42 weeks, ascribed to fetal distress,
which presumably could have occurred and resulted
in similar management difficulties during earlier
induction. This death was plausibly preventable
by induction at 41 weeks, as was a stillbirth
in another study[ 14 ] from massive abruption
at 41+5 weeks. However, 2600 grammes is an abnormal
birthweight in Canada for 42 weeks of gestation,
so the hypothesis that death occurred as a result
of gestation alone is dubious.
Thus of seven perinatal deaths in 3002 women
randomised to expectant management, only two occurred
in women who received contemporary fetal testing,
before 43 weeks, from a cause possibly related
to pregnancy duration. This is against one death
in the induction group. The higher risk that routine
induction at 41 weeks aims to reduce is dubious,
if it exists at all.
3. What are the maternal risks of reaching 41
weeks of gestation?
The SOGC Clinical Practice Guidelines asserts
that "women who reach 41 weeks of gestation
should be counselled appropriately regarding the
higher risks to themselves...if they should pursue
a policy of expectant management"[ 3 ].
Bias arising from improperly executed randomised
designs threatens, and potentially invalidates,
the conclusions of such efforts. Avoiding such
errors requires not only eliminating bias from
entry allocation, but also differing treatment.
The Canadian study found that "the rate of
cesarean section was significantly higher among
women in the monitoring group (24.5%) than among
those in the induction group (21.2%)"[ 2
]. Its authors admit a bias that might have accounted
for part of the induction cohort's lower rate
of caesarean section, that prostaglandin gel was
used for cervical ripening only in that arm of
the trial.
Although the authors acknowledged later that
"use of prostaglandin gels appears to be
the best method for inducing labour, particularly
when the cervix is unfavourable"[ 15 ], prostaglandin
was proscribed in the expectant cohort "because
we thought that most of the women in that group
who would require induction of labour would have
evidence of fetal compromise"[ 2 ].
In fact, a third (34%) of the women in the monitoring
group were induced, but only half of them (17%
overall) for 'fetal compromise', with the nature
and validity of that generalisation undefined.
The above-mentioned rationalisation for withholding
prostaglandin from the monitoring group implies
that the method was believed to be too dangerous
given possible fetal compromise. It is more logical
that suspected fetal compromise would make reduction
in the number of contractions needed to accomplish
vaginal delivery desirable.
Thus, prostaglandin cervical ripening would
be indicated, not contraindicated, and rationalisation
in the Canadian trial's is a non sequitur.
A second bias that could have contributed to
the higher rate of caesarean section in the expectant
cohort is that the trial was not blinded. Both
accoucheurs and patients knew that what was being
assessed was whether it was safe to let pregnancy
continue past 41 weeks. It is likely that as the
duration of pregnancy extended, both groups would
have felt increasing pressure to intervene, possibly
with caesarean section, in this so-called and
so-conceived high risk situation. This assertion
is not hypothetical, rather probable, given the
revelations of Tversky and Kahneman about how
humans make decisions in the presence of uncertainty[
16 ].
There is a third important bias which could lead
to greater use of caesarean section in the monitoring
cohort.
Within that group, 17% of women were believed
to have sufficient evidence of fetal compromise
that "the fetus was to be delivered immediately"[
2 ]. Envision a woman randomised to the expectant,
possibly conceptually high risk group. The clinician
is told that monitoring indicates that the fetus
is 'compromised' or in distress and should "be
delivered immediately". In such enhanced
alarm, tolerance of typically benign intrapartum
fetal heart rate changes or the passage of meconium
would be reduced, and caesarean section for such
imprecise signals would be more likely[ 17 ].
There is considerable evidence for such behavioural
bias in obstetric settings, and that obstetric
thinking confirms in vivo what Tversky and Kahneman
described as the availability error[ 16 ]. The
Toronto Tri-hospital trial revealed that labelling
a woman gestational diabetic conferred a doubled
rate of caesarean section, regardless of the fetal
or maternal condition, and with no relationship
to birthweight[ 18 ].
Elsewhere, false positive prediction by ultrasound
of macrosomia provoked a 50% increase in caesarean
delivery of same weight babies[ 19 ]. In a German
study, the label growth retardation biased interpretation
of, and action taken for, fetal cardiotocography
and led to twice as many caesarean sections as
occurred in undetected cases of growth restriction[
20 ].
In a Swedish study, older nulliparae had dramatically
increased odds of caesarean delivery, regardless
of maternal or fetal condition[ 21 ]. A study
from Iceland and Scotland of 522 twin pregnancies
in 1990-1993 revealed no difference in management
or outcomes of natural ( n = 453) versus assisted
( n = 69) conceptions, except that elective caesarean
delivery was twice as likely in the assisted conception
group[ 22 ].
A Canadian study of the definition and management
of dystocia found that among the strongest determinants
of a decision for casesarean section were acquisition
of a dystocia perception and label, or its equivalent
in the mind of the attending physician and the
hospital in which the decision was made, although
a significant proportion of such decisions were
made before active labour[ 23 ].
The higher rate of caesarean sections in the
Canadian study's expectant group was almost completely
accounted for by more operations for fetal distress
[8.3 versus 5.7%][ 2 ]. The authors suggested
this occurred because fetuses become progressively
compromised and more prone to intrapartum fetal
distress as pregnancy becomes more post-term.
An alternative, better substantiated explanation
is that monitoring created and reinforced bias
toward inference of fetal distress and made it
more likely that caesarean delivery would be the
response to that inference. Imprecision of the
term fetal distress in obstetric care, despite
its liberal use, promotes the availability error
in decision making, given uncertainty[ 16 ].
As the true risk, in contrast to the perceived
risk, of a fetus dying between 41 and 42 weeks,
in the absence of monitoring, is only 0.1%, it
is extremely unlikely that the 17% of fetuses
in the expectant group believed to be compromised
were actually in trouble. Over 99% of the supposedly
compromised fetuses detected by monitoring most
likely were not, but were rescued from normalcy
by operative delivery for enhanced provider and
patient anxiety.
The assertion that induction at 41 weeks results
in fewer caesarean sections than expectant management
is doubtful at best. It is particularly difficult
to reconcile with considerable and consistent
evidence that induction, especially in nulliparae
with unfavourable cervices, markedly increases
the rate of caesarean sections[ 24, 25, 26, 27,
28, 29, 30, 31, 32 ]. In a four-year period in
southern Alberta, the caesarean rate for women
induced in their 41st week was 23%, compared with
14% in those who laboured spontaneously in the
41st week[ 32 ]. The SOGC cautioned against induction
before 41 weeks, in that "particularly in
nulligravida...the likelihood of cesarean section
may be twice as great when labour is induced as
compared with spontaneous"[ 3 ].
Why this should not be the case for induction
at 41 weeks is unexplained, and unlikely. Given
the odds of stillbirth of 0.1% in the 41st week
without induction for dates alone or special fetal
surveillance, the influence of fetal risk is more
likely that of perception than reality.
One of the most influential biases in the acquisition
of evidence is choice of the question, and the
best evidence in answer to the wrong question
is useless. The rate of caesarean section were
reported in the Canadian study by intention-to-treat,
but they should be analysed also as actually treated.
In the intended-to-induce group, 31% of women
were not induced, and in the intended-not-to-induce
cohort, 34% of women were induced.
In essence, one-third of each cohort were treated
by the opposite method to that intended. In that
true fetal compromise is rare at 41 weeks, the
Canadian study was comparing elective induction
compared with expectant management at 41 weeks.
Comparing the rates of caesarean section in all
women induced versus all women who laboured spontaneously
at 41 weeks would be a more valid test of whether
induction at 41 weeks alters the caesarean rate,
or conveys any other advantage or disadvantage.
One can estimate the results presented as 'treatment
actually received' using the Canadian study's
reported percentage of women in each group treated
by the method intended (Fig. 1a and b). Assuming
a rate of caesarean section of 16% in women starting
spontaneous labour, regardless of intention-to-treat
allocation, one would obtain a caesarean rate
of 16% in women who laboured spontaneously compared
with 29% in those who were induced. If one recalculates
using the 14% caesarean rate for spontaneous labour
at 41 weeks in Alberta in the early 1990s[ 32
], this difference becomes even more striking.
(11.4 KB)Fig. 1: (A) The numbers of women and
caesareans at the bottom of the vertical columns
from Hannah[ 15 ]. The numbers in each cell are
estimates derived from ref. [ 2 ]; (B) the results
if one assumes a 16% caesarean rate in women who
start labour spontaneously. The numerators are
numbers of caesareans, the denominators are numbers
of women, and in parentheses is the percentage
of caesarean sections.
The appropriate counselling "regarding the
higher risks to themselves", that the SOGC
Clinical Practice Guidelines assert must be provided
to women who reach 41 weeks of gestation, should
be that the higher risk is of caesarean delivery
for dubious reasons, and that to avoid it they
should labour and deliver where induction for
dates alone is not the ritual at 41 weeks of gestation.
Despite excluding women with medical or fetal
problems, an urgent need for delivery or contraindications
to vaginal delivery, 31% of nulliparous women
in the Canadian study were delivered by caesarean
section[ 15 ]. Rather than establishing the case
for routine induction at 41 weeks, the results
of the Canadian trial reflect the high intervention
rates of obstetric practice in Canada, which has
the second highest rate of caesarean section in
the developed world[ 33 ].
Given this specific intervention epidemic, it
may be appropriate to note as well that since
previous caesarean section was an exclusion criterion,
the conclusions of the Canadian study even if
valid, would be inapplicable to women in such
circumstances.
4. Resource consequences of a policy of routine
induction at 41 weeks of gestation
Left alone, a significant proportion of pregnancies
are undelivered by 41 weeks of gestation. In one
study using ultrasound dating, 19% of women were
undelivered at 41 weeks, whereas only 3.5% were
undelivered at 42 weeks[ 34 ]. In the aforementioned
Swedish study, 30% of nulligravidae reached 287
days undelivered whereas 10% reached 294 days[
7 ]. In our setting, 23% of women undelivered
by 36 weeks remained as such at 41 weeks versus
7.5% at 42 weeks - (Table: [ 2].
Although proportions of pregnancies undelivered
by 41 versus 42 weeks vary between populations,
depending in part on the use of ultrasound dating[
35 ], about 15%-20% more women will be induced
given routine induction at 41 as opposed to 42
weeks. Using an annual delivery volume of 4000
births per year, about 1000 inductions would be
done solely because gestation had reached 41 weeks,
versus 140-400 per year (3.5%-10%) if induction
for gestation only was deferred to 42 weeks.
Presuming that hospitals would reserve such induction
for otherwise untroubled mothers and fetuses to
five weekdays in each of 52 weeks, a hospital
with 4000 births per year would have to provide
for three added inductions per day, given a policy
of such interference at 41 weeks. These would
be in addition to those indicated for legitimate
and significant maternal or fetal threat. This
is a staggering imposition, given that at least
500 and more likely over 1000 inductions must
be done to prevent one perinatal death from unspecified
relationships to gestation.
We anticipate at least two objections to this
analysis. One is that the SOGC Clinical Practice
Guidelines do not state explicitly that induction
must occur at 41 weeks zero days. The document
is written vaguely enough to be interpreted that
induction any time between 41 weeks zero days
and 41 weeks six days is acceptable.
However, in response to the Clinical Practice
Guidelines, Canadian obstetricians, at least the
ones in the authors' hospitals, now book induction
by, if not before, one week past the supposed
due date, ignoring the modifier 'estimated', as
well as biologic norms and realities. They fear
medico-legal implications should the fetus die
at seven or more days past the due date, with
no regard for the true odds and likely causation
of such outcomes.
The adverse consequences of Clinical Practice
Guidelines have been described in various situations[
36, 37, 38 ]. Lest we be perceived as criticising
the best intentions of our competent and caring
colleagues, the nonsensus consensus about management
of uncomplicated undelivered pregnancy at 41 weeks
is simply a Clinical Practice Guidelines-reinforced
example of the availability error.
Thereby, adversity odds are significantly overestimated,
normally odds are even more significantly underestimated,
and both logic and behaviour are warped as a result[
16 ].
A second anticipated objection is "Those
to be induced at 41 weeks must labour and deliver
sooner or later, so what is the difference?"
The difference is between arriving in labour and
delivering 5-10 hours later compared with induction
with an unfavourable cervix, requiring ripening
with its variable success, then labour for 10
hours or more. The workload increment for nursing,
midwifery and medical staff is significant given
the need to induce 15%-20% more of the pregnant
population, and in that improved outcomes are
dubious, indefensible.
5. Inevitable, unintended and undesirable consequences
of routine induction at 41 weeks
Greatly increased obstetric workload may be argued
to be an acceptable imposition because, otherwise,
one baby in 1000 reaching 41 weeks might die.
We concede that, rarely, one such fetus might
be saved. No test of fetal wellbeing is or likely
ever will be perfect.
But it is uncertain that routine induction at
41 weeks will reduce the number of fetuses who
die, and it is arguable that such practice could
increase perinatal mortality and morbidity. Attention
is a limited resource[ 39 ]. The extra attention
needed for such added induction and its consequences
will draw attention away from women labouring
spontaneously or who are being induced for more
compelling reasons. A mother, or a fetus of less
than 41 weeks who needed help, harmed because
people were busy with somebody else who did not
need help, will not be counted in morbidity and
mortality analysis of intervention by induction
of labour at 41 weeks of gestation.
In one of the authors' hospitals, a pregnant
woman admitted because of hypertension complained
of headaches while her blood pressure rose to
170/110 mmHg. Intravenous antihypertensive drugs
were allowed to be given only on the labour floor.
Transfer to the labour floor was delayed because
there were no beds available, several being filled
with 41-week inductions. The woman died from intracranial
haemorrhage before transfer. Anecdotes are not
the singular source of evidence.
But we wonder, whenever near-misses, near-catastrophes
or true disasters occur on labour wards, whether
they could have been anticipated and prevented
had the staff not been so busy. As was stated
in another context "preoccupation with the
potential benefit to the numerator may make doctors
less sensitive to the adverse effects on the population"[
40 ].
The Canadian trial[ 2 ] resulted in a grave which
we discovered during research into cervical cord
injury[ 41 ]. A mother randomised to induction
was induced, with prostaglandin. Precipitate labour
ensued, with rapid progress to full dilation,
severe decelerations, forceps rotation and extraction.
The baby sustained high cervical cord injury and
quadriplegia. This complication was not identified
in the publication[ 2 ], a subsequent reinterpretation[
15 ], nor in the SOGC Clinical Practice Guidelines[
3 ] and there was no such incident in the study's
expectant cohort.
6. Conclusion
The median and mode for uncomplicated singleton
pregnancy are 40 weeks two days and 40 weeks three
days, respectively[ 42, 43 ], not '40 weeks',
and two standard deviations beyond that is approximately
13 days.
Approximately one-quarter of pregnant women have
not laboured by 41 weeks. Their stillbirth rate
in the subsequent week without fetal surveillance
is approximately 1 in 1000. Routine induction
at 41 weeks is ritual induction at term, unsupported
by rational evidence of benefit. It is unacceptable,
illogical and unsupportable interference with
a normal physiologic situation.
Two decades ago it was argued "that any
infant born at term should survive, provided the
infant has no lethal malformation"[ 44 ].
If only a fragment of such hyperbole is used to
rationalise ritual induction at 41 weeks, to be
logically consistent, we should induce everybody
at 40, or perhaps 39, or 38, or even 37 weeks.
Although the stillbirth rate at those earlier
gestations is less than at 41 weeks, the absolute
number of fetuses who die is greater.
Since more babies die at those gestations than
die in week 41 - (Tables: [ 2, 3], more lives
could- we have not written would-be saved.
Table 3: Number of stillbirths at each week of
gestation. (5.43 KB)
Almost a quarter of a century ago, the prescient
authors of an article entitled Intervention and
Causal Inferences in Obstetric Practice cautioned
that "as ... interventions are applied to
an increasingly large proportion of the obstetric
and fetal population, a threshold will inevitably
be reached beyond which the marginal risks of
the procedure will outweigh the marginal benefits"[
45 ].
The 'evidence' on which current practice and
popularity of routine or as we prefer to think
of it, ritual induction at 41 weeks, is based
is seriously flawed and an abuse of biological
norms. Such interference has the potential to
do more harm than good, and its resource implications
are staggering. It is time for this nonsensus
consensus to be withdrawn.
References
1. Crowley P. Interventions to prevent or improve
outcome from labour at or beyond term. The Cochrane
Library, Oxford: Update Software Issue 1:2001.
2. Hannah ME, Hannah WJ, Hellmann J, Hewson S,
Milner R, Willan A, Canadian Multicenter Post-term
Pregnancy Trial Group "Induction of labor
as compared with serial antenatal monitoring in
post-term pregnancy. A randomized controlled trial",
N Engl J Med, Volume: 326, (1992), pp. 1587-1592
3. Maternal-Fetal Medicine Committee of the Society
of Obstetricians and Gynaecologists of Canada.
Post-term pregnancy (Committee Opinion). SOGC
Clinical Practice Guidelines, No. 15, 1997.
4. Hall PF, "The consensus cult", J
Soc Obstet Gynaecol Can, Volume: 22, (2000), pp.
8
5. Feldman GB, "Prospective risk of stillbirth",
Obstet Gynecol, Volume: 79, (1992), pp. 547-553
6. Minakami H, Kimura H, Honma Y, Tamada T, Sato
I, "When is the optimal time for delivery?-purely
from the fetuses' perspective", Gynecol Obstet
Invest, Volume: 40, (1995), pp. 174-178
7. Ingemarsson I, Kallen K, "Stillbirths
and rate of neonatal deaths in 76,761 post term
pregnancies in Sweden, 1982-1991: a register study",
Acta Obstet Gynecol Scand, Volume: 76, (1997),
pp. 658-662
8. Hilder L, Costeloe K, Thilaganathan B, "Prolonged
pregnancy: evaluating gestation-specific risks
of fetal and infant mortality", Br J Obstet
Gynaecol, Volume: 105, (1998), pp. 169-173
9. Widjaja AH, Mantell CD, "Stillbirths
in Auckland 1983-1986", NZ Med J, Volume:
101, (1988), pp. 768-770
10. Yudkin PL, Wood L, Redman CWG, "Risk
of unexplained stillbirth at different gestational
ages", Lancet, Volume: 1, (1987), pp. 1192-1194
11. Henry GR, "A controlled trial of surgical
induction of labour and amnioscopy in the management
of prolonged pregnancy", J Obstet Gynaecol
Br Commonw, Volume: 76, (1969), pp. 795-798
12. Bergsjø P, Gui-dan H, Su-qin Y, Zhi-zeng
G, Bakketeig L, "Comparison of induced versus
non-induced labour in post-term pregnancy: a randomized
prospective study", Acta Obstet Gynecol Scand,
Volume: 68, (1989), pp. 683-687
13. Dyson DC, Miller PD, Armstrong MA, "Management
of prolonged pregnancy: induction of labor versus
antepartum fetal testing", Am J Obstet Gynecol,
Volume: 156, (1987), pp. 928-934
14. Cardozo L, Fysh J, Pearce JM, "Prolonged
pregnancy: the management debate", BMJ, Volume:
293, (1986), pp. 1059-1063
15. Hannah ME, "Postterm pregnancy: should
all women have labour induced? A review of the
literature", Fet Mat Med Rev, Volume: 5,
(1993), pp. 3-17
16. Tversky A, Kahneman D, Judgment Under Uncertainty:
Heuristics and Biases, (1982), Cambridge University
Press, Cambridge.
17. Alfirevic Z, Walkinshaw SA, "A randomized
controlled trial of simple compared with complex
antenatal fetal monitoring after 42 weeks of gestation",
Br J Obstet Gynaecol, Volume: 102, (1995), pp.
638-643
18. Naylor CD, Sermer M, Chen E, Sykora K, "Cesarean
delivery in relation to birth weight and gestational
glucose tolerance: pathophysiology or practice
style?", JAMA, Volume: 275, (1996), pp. 1199-1200
19. Levine AB, Lockwood CJ, Brown B, Lapinski
R, Berkowitz RL, "Sonographic diagnosis of
the large for gestational age fetus at term: does
it make a difference?", Obstet Gynecol, Volume:
79, (1992), pp. 55-58
20. Jahn A, Razum O, Berle P, "Routine screening
for intrauterine growth retardation in Germany:
low sensitivity and questionable benefit for diagnosed
cases", Acta Obstet Gynecol Scand, Volume:
77, (1998), pp. 643-648
21. Cnattingius R, Cnattingius S, Notzon FC,
"Obstacles to reducing cesarean rates in
a low-cesarean setting: the effect of maternal
age, height, and weight", Obstet Gynecol,
Volume: 92, (1998), pp. 501-506
22. Agustsson T, Geirsson RT, Mires G, "Obstetric
outcome of natural and assisted conception twin
pregnancies is similar", Acta Obstet Gynecol
Scand, Volume: 76, (1997), pp. 45-49
23. Stewart PJ, Duhlberg C, Arnett AC, Elmslie
T, Hall PF, "Diagnosis of dystocia and management
with caesarean section among primiparous women
in Ottawa Carleton", CMAJ, Volume: 142, (1990),
pp. 459-463
24. Xenakis EM-J, Piper JM, Conway DL, Langer
O, "Induction of labor in the nineties: conquering
the unfavourable cervix", Obstet Gynecol,
Volume: 90, (1997), pp. 235-239
25. Smith LP, Nagourney BA, McLean FH, et al.
"Hazards and benefits of elective induction
of labor", Am J Obstet Gynecol, Volume: 148,
(1984), pp. 579-585
26. Macer J, Macer CL, Chan LS, "Elective
induction versus spontaneous labor: a retrospective
study of complications and outcome", Am J
Obstet Gynecol, Volume: 166, (1992), pp. 1690-1697
27. Buist R, Ranchhod N, "Induction of labour:
indications and obstetric outcomes in a tertiary
referral hospital", N Z Med J, Volume: 112,
(1999), pp. 151-153
28. Maslow AS, Sweeny AL, "Elective induction
of labor as a risk factor for cesarean delivery
among low risk women at term", Obstet Gynecol,
Volume: 95, (2000), pp. 917-922
29. Coonrod DV, Bay RC, Kishi GY, "The epidemiology
of labor induction: Arizona, 1997", Am J
Obstet Gynecol, Volume: 182, (2000), pp. 1355-1362
30. Seyb ST, Berca RJ, Socol ML, Dooley SL, "Risk
of cesarean delivery with elective induction of
labor at term in nulliparous women", Obstet
Gynecol, Volume: 94, (1999), pp. 600-607
31. Yeast JD, Jones A, Poskin M, "Induction
of labor and the relationship to cesarean delivery:
a review of 7001 consecutive inductions",
Am J Obstet Gynecol, Volume: 180, (1999), pp.
628-633
32. Lange I, Page R, Mah A, Yee J, "Comparison
of LSCS rates for induced vs spontaneous labour
in low risk primigravids [poster presentation
SOGC Conference, Calgary, Alberta]", Southern
Alberta Perinatal Audit Program Bulletin, Volume:
5, Issue: 2 (1995),
33. Stephenson PA, Bakoula C, Hemminki E, et
al. "Patterns of use of obstetrical interventions
in 12 countries", Paediatr Perinat Epidemiol,
Volume: 7, (1993), pp. 45-54
34. Mongelli M, Wilcox M, Gardosi J, "Estimating
the date of confinement: ultrasonographic biometry
versus certain menstrual dates", Am J Obstet
Gynecol, Volume: 174, (1996), pp. 278-281
35. Goldenberg RL, Davis RO, Cutter GR, Hoffman
HJ, Brumfield CG, Foster JM, "Prematurity,
postdates, and growth retardation: the influence
of use of ultrasonography on reported gestational
age", Am J Obstet Gynecol, Volume: 160, (1989),
pp. 462-470
36. McIntyre KM, "Medicolegal implications
of consensus statements", Chest, Volume:
108, Issue: Suppl (1995), pp. 502S-505S
37. Hyams AL, Brandenburg JA, Lipsitz SR, Shapiro
DW, Brennen TA, "Practice guidelines and
malpractice litigation: a two-way street",
Ann Intern Med, Volume: 122, (1995), pp. 450-455
38. Hirshfeld EB, "Should practice parameters
be the standard of care in malpractice litigation?",
JAMA, Volume: 266, (1991), pp. 2886-2891
39. Cook RI, Woods DD, "Operating at the
sharp end: the complexity of human error",
Bogner MS, (Ed.) Human Error in Medicine, (1994),
pp. 255-310 Lawrence Erlbaum Associates, Hillsdale,
NJ.
40. Woolf SH, Kamerow DB, "Testing for uncommon
conditions: the heroic search for positive results",
Arch Int Med, Volume: 150, (1990), pp. 2451-2458
41. Menticoglou SM, Perlman M, Manning FA, "High
cervical spinal cord injury in neonates delivered
with forceps: report of 15 cases", Obstet
Gynecol, Volume: 86, (1995), pp. 589-594
42. Bergsjø P, Denman DW, Hoffman HJ,
Meirik O, "Duration of human singleton pregnancy:
a population based study", Acta Obstet Gynecol
Scand, Volume: 69, (1990), pp. 197-207
43. Baskett TF, Nagele F, "Naegele's rule:
a reappraisal", Br J Obstet Gynaecol, Volume:
107, (2000), pp. 1433-1435
44. Stubblefield PG, Berek JS, "Perinatal
mortality in term and post-term births",
Obstet Gynecol, Volume: 56, (1980), pp. 676-682
45. Chalmers I, Richards M, "Intervention
and causal inferences in obstetric practice",
Chard T, (Ed.) Benefits and hazards of the new
obstetrics, Clin Devel Med, Volume: 64, (1977),
pp. 34-61
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