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The Obstetrician & Gynaecologist
Review Management of large-forgestational-age pregnancy in
non-diabetic women
Authors San San Aye / Veronica Miller / Saloni Saxena / Mohamad Farhan
Key content:
• Over the last two to three decades there has been a 15–25% increase in many countries
in the number of women giving birth to large infants.
• Rates of shoulder dystocia and caesarean birth rise substantially at 4000 g and again
at 4500 g.
• There is an increase in maternal and neonatal morbidity associated with fetal macrosomia.
• Serial measurement of fundal height adjusted for maternal physiological variables
substantially improves antenatal detection.
• Sonographic assessment of fetal weight is frequently inaccurate.
• Induction of labour for suspected macrosomia in non-diabetic women has not been shown
to reduce the risk of caesarean section, instrumental delivery or perinatal morbidity.
Learning objectives:
• To identify the risks associated with fetal macrosomia and to be aware of the long-term
implications.
• To understand the limitations of predictive tools.
• To be able to take an informed approach to managing the macrosomic fetus.
Ethical issues:
• To what extent should the fear of medico-legal action influence obstetricians’
management of suspected fetal macrosomia?
• What advice should clinicians give women regarding modes of delivery?
Keywords birth weight / estimated fetal weight / induction of labour / macrosomia /
shoulder dystocia
Please cite this article as: Aye SS, MillerV, Saxena S, Farhan M. Management of large-for-gestational-age pregnancy in non-diabetic women. The Obstetrician & Gynaecologist 2010;12:250–256.
Author details
San San Aye MMedSc MRCOG
Consultant Obstetrician and Gynaecologist
North Devon District Hospital, Raleigh Park,
Barnstaple, Devon EX31 4JB, UK
Email: [email protected]
(corresponding author)
250
Veronica Miller MRCOG
Consultant Obstetrician and Gynaecologist
Stoke Mandeville Hospital, Mandeville Road,
Aylesbury, Buckinghamshire HP21 8AL, UK
Saloni Saxena MBBS
Senior House Officer in Obstetrics
and Gynaecology
University Hospital Lewisham, Lewisham
High Street, London SE13 6LH, UK
Dr Mohamad Farhan MBBS
Senior House Officer in Obstetrics
and Gynaecology
Wycombe General Hospital, Queen
Alexandra Road, High Wycombe,
Bucks HP112TT, UK
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Introduction
There has been a rise in the prevalence of large
newborns in many parts of the world. Over the last
two to three decades, an overall 15–25% increase in
the proportion of women giving birth to large
infants has been documented in the USA, Canada,
Germany, Scotland and Denmark.1–5 This trend has
been attributed to increases in maternal height,
body mass, gestational weight gain and diabetes;
reduced maternal cigarette smoking; and changes
in sociodemographic factors.2,4 The prevalence of
liveborn infants weighing 4000 g was 11.65% in
our institution (Wycombe Hospital, UK) in 2008.
It is known that there is an increase in maternal
and neonatal morbidity associated with fetal
macrosomia. However, there is no universal
consensus on the definition, diagnosis and
antenatal management of fetal macrosomia. In this
review, we try to provide a sensible approach to
management of large-for-gestational-age (LGA)
pregnancies in non-diabetic women based on the
available evidence.
Search strategy
Electronic searches of literature published between
1980 and 2009 were undertaken using MEDLINE,
Embase, CINHAL, the Cochrane Database of
Systematic Reviews and the National Institute for
Health and Clinical Excellence (NICE) website.
Search items included: pregnancy, fetal
macrosomia, foetal macrosomia, macrosomic
fetus, large for dates, large for gestational age and
macrosomia, combined with the terms nondiabetic, brachial plexus injury, shoulder dystocia,
antenatal care, perinatal care and management.
Terms were connected by the Boolean operator
‘OR’. This retrieved a total of 312 references and,
after exclusion of duplicate and obviously
irrelevant papers, 60 studies published in the
English language or with an English language
abstract were identified.
Terminology
The term large-for-gestational-age has mainly been
used for fetuses or newborns with an (estimated)
weight 90th percentile or 2 standard deviations
from the mean for the gestational age.6–8 The
Ponderal Index is an indicator of body proportions
of infants, defined as body weight divided by the
third power of length (g/cm3). Macrosomia is a term
mostly used for newborns with a birth weight above
a certain limit. However, there is no consensus as to
what this limit should be. Birth weights 4000 g,
4200 g and 4500 g are used as definitions of
newborn macrosomia.6–8 Generally, it seems
appropriate to consider a fetus or newborn with an
estimated or actual birth weight 4000 g as
macrosomic,6,9 especially in cases of insulindependent diabetes mellitus.6 However, it is more
important to supplement the term fetal macrosomia
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with information about body proportions,
composition and metabolic characteristics,
which are determinants of short-term obstetric
complications and long-term health problems.
In this article, we will define LGA fetuses as those
with an (estimated) birth weight 4500 g.9–12
Risk factors and obstetric
complications associated
with macrosomia
In an American cohort study, Stotland et al.9
identified the risk factors associated with neonatal
birth weight 4500 g. Male infant sex, multiparity,
maternal age 30–40 years, white race, diabetes and
gestational age 41 weeks appeared to be
associated risk factors (P 0.001). Adverse
obstetric outcomes were also studied in this cohort.
Women who delivered a macrosomic infant were
more likely to undergo caesarean birth and to suffer
shoulder dystocia, chorioamnionitis, fourth-degree
perineal lacerations, postpartum haemorrhage and
longer hospital stay. Adjusted odds ratios (ORs) for
caesarean birth of birth weight groups 4000–4499 g,
4500–4999 g and 5000 g were 1.69, 2.99 and 5.46;
and for shoulder dystocia were 6.29, 13.05 and
17.52, respectively.9 Limitations of this study are
secondary data analysis, lack of data on
confounding factors and the study group being
a cohort of privately insured patients.
On the other hand, the evidence showed no
differences in adverse birth outcomes between birth
weights of 3500–3999 g and those of 4000–4499 g.10
High birth weight (4500–4999 g) and very high birth
weight (5000 g) were found to be associated with
early neonatal death; the leading cause of death was
asphyxia. The majority of post-neonatal deaths were
caused by sudden infant death syndrome.Very high
birth weight infants were twice as likely to die of
sudden infant death syndrome as normosomic
infants, whereas high birth weight infants were not at
increased risk.10 The risk of shoulder dystocia rises
from 1.4% for all vaginal deliveries to 9.2–24% for
birth weights 4500 g.11
The American College of Obstetricians and
Gynecologists defines macrosomia as birth weight
4500 g, irrespective of gestational age, as both
maternal complications and perinatal morbidity
and mortality begin to rise from that birth weight.12
Long-term health risks
Meta-analysis of the 14 studies that examined the
association between birth weight and risk of type 2
diabetes in later life showed a U-shaped association.
Low birth weight (2500 g) and high birth weight
(4000 g) were associated with increased risk of
type 2 diabetes.13 Size at birth, particularly length
and head circumference, is associated with
increased risk of breast cancer in premenopausal
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women after adjustment for adult risk factors and
birth weight.14 A population-based cohort study by
Sin et al.15 determined the relationship between
birth weight and risk of emergency visits for asthma
during childhood. Those with a high birth weight
had a significantly increased number of visits and
the relationship was linear if birth weight was
4500 g, such that every increment of 100 g in
birth weight was associated with an additional 10%
increase in the risk of emergency visits. A number
of very large, well-conducted studies have shown an
association between birth weight and subsequent
body mass index (BMI) (kg/m2) or overweight, at
least for young white adults and children. By
contrast, several studies have shown no association
in middle-aged subjects, although these were fairly
small studies. Genetic factors were predominant in
this association, especially with BMI in adulthood.16
Diagnosis of fetal macrosomia
(See Figure 1.) Clinical estimations are based on
palpation of the uterus and measurement of the
height of the fundus of the uterus; both are subject
to considerable variation.
Fundal height measurements are an inaccurate way
of estimating fetal size. They are influenced by the
maternal size, amount of amniotic fluid, status
Figure 1
Algorithm for the diagnosis of LGA
pregnancy in non-diabetic women.
At all stages of management, it is
crucial to obtain the woman’s
agreement
of the bladder, pelvic masses (e.g. fibroids), fetal
position and many other factors.
Serial measurements of fundal height adjusted
for maternal physiological variables such as age,
weight, height, ethnicity, parity and birth weight
in previous pregnancies, significantly increase
the antenatal detection of LGA babies (the
detection rate was 46% in the study group
compared with 24% in the control group; OR
2.6; confidence interval [CI] 1.3–5.5). This is
followed by fewer investigations and, hence, is a
cost-effective screening tool for fetal growth in
the community. To improve assessment of fetal
growth it is critical that the measurements are
taken serially rather than done as a one-off
measurement.17
Ultrasonographic prediction
of fetal macrosomia
Ultrasound measures used for predicting a
macrosomic fetus are either single parameters
(such as abdominal circumference or subcutaneous
tissue thickness) or combinations of measurements
to estimate fetal weight. Ultrasound biometry used
to detect fetal weight 4000 g is characterised by
low sensitivity, low positive predictive value and
high negative predictive value.18,19
Clinically LGA at 36 weeks of gestation by
palpation
SFH >90th centile confirmed on personalised
growth chart
Ultrasound biometry, including AFI
EFW >90th centile and increased AFI
Check glucose in urine, GTT at booking visit,
previous history of gestational diabetes mellitus
Increased AFI or glucose in urine
Arrange GTT34,35
Normal GTT
Follow primiparous or
multiparous pathway (Figure 2
and Figure 3)
Abnormal GTT
Refer to diabetes team
AFI = amniotic fluid index; EFW = estimated fetal weight; GTT = glucose tolerance test;
SFH = symphysio–fundal height
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A systematic quantitative review of 63 accuracy
studies21 (which included 51 evaluating the
accuracy of estimated fetal weight [EFW] and
12 evaluating the accuracy of fetal abdominal
circumference, including a total of 19 117 women)
assessed ultrasonographically-estimated fetal
weight and abdominal circumference in the
prediction of macrosomia. The summary receiver
operating characteristic curve (sROC) area for
EFW was not different from the area for fetal
abdominal circumference (0.87 versus 0.85,
P 0.91), suggesting that there was no difference in
accuracy between ultrasonographically-estimated
fetal weight and abdominal circumference in the
prediction of a macrosomic baby at birth. For
predicting a birth weight of 4000 g, the summary
likelihood ratios (LRs) were 5.7 (95% CI 4.3–7.6)
for a positive test and 0.48 (95% CI 0.38–0.60) for a
negative test, using Hadlock et al.’s formula of
estimating fetal weight ultrasonographically.20
For ultrasound fetal abdominal circumference of
36 cm, the respective LRs for predicting birth
weight 4000 g were 6.9 (95% CI 5.2–9.0) and 0.37
(95% CI 0.30–0.45). A positive test result is more
accurate at ruling in macrosomia than a negative
test result at ruling it out.21
Similarly, ROC curves indicated that measurements
of soft tissue are not superior to clinical or other
sonographic predictions in identifying fetuses with
weights of 4000 g, although the study had limited
power.22
Combinations of amniotic fluid index and EFW
measurements during the middle of the third
trimester are useful predictors of macrosomia at
birth. Combined analysis of amniotic fluid index
60th percentile and EFW 71st percentile
resulted in a positive predictive value of 85%.23
Several studies24,25 have compared clinical with
ultrasound estimation of birth weight and none of
these have demonstrated ultrasound to be superior
to clinical estimation. Both clinical and
sonographic predictions of macrosomia include
areas of the ROC curve between 0.81 and 0.95,
which is defined as useful from a statistical point
of view. However, predictions of macrosomia by
these techniques are limited by the substantial
false-positive and false-negative rates inherent in
these tests.26
There are some studies that suggest ways to
improve the predictive accuracy of fetal
macrosomia. Serial sonographic measurements can
increase the positive predictive value.19 However,
serial biometry is time consuming and the cost
effectiveness is questionable. Regardless of the
formula used, the accuracy of sonographic estimates
decrease with increasing birth weight.19 Threedimensional ultrasound and magnetic resonance
© 2010 Royal College of Obstetricians and Gynaecologists
2010;12:250–256
Review
imaging (MRI) are expected to be additional tools in
future to estimate fetal weight and even body
composition, but their usefulness needs to
be further investigated.19,27,28 A software program
(a customised fetal growth chart) that calculates on
the basis of pregnancy variables entered at the first
visit provides an adjusted normal range for that
particular fetal size and is, thus, more specific.
Using the program, 22% of those designated large
(90th centile) on the standard population growth
chart were within normal limits for the pregnancy.
Conversely, 26% of babies identified as large, with
adjusted centiles, were ‘missed’ by conventional
unadjusted centile assessment. Adjustment for
physiological variables makes assessment of fetal
growth more precise and reduces unnecessary
interventions and parental anxiety.29,30 Similarly,
computerised combinations of a number of risk
factors such as diabetes and twin pregnancy may
also improve identification of macrosomia.31
Other predictors of macrosomia
A change in maternal BMI during pregnancy has an
independent positive predictive value for fetal
macrosomia. An increase in BMI 25% during
pregnancy has a sensitivity of 86.2%, specificity of
93.6%, positive predictive value of 71.4% and
negative predictive value of 97.45% for
macrosomia.32
Women with a history of one macrosomic infant
are at significantly increased risk of another
macrosomic infant in a subsequent pregnancy. For
women with two or more macrosomic infants, the
risk is even greater.33
Management
Management of pregnancies with suspected fetal
macrosomia (Figure 2, Figure 3 and Box 1) is
challenging for clinicians. Elective caesarean
section is intended to prevent several of the
complications associated with fetal macrosomia,
especially brachial plexus injuries and maternal
perineal lacerations. However, it has been
estimated that 3600 caesarean deliveries need
to be performed in non-diabetic women with
suspected fetal macrosomia (4500 g) to
prevent a single permanent brachial plexus
injury.36 Thus, elective caesarean section for the
sole indication of macrosomia cannot be
justified.
Clinical research, in conjunction with costeffectiveness analyses, has led to the consensus that
elective caesarean delivery is only beneficial for
non-diabetic women whose fetus is suspected to be
5000 g.37,38
Before caesarean section became reasonably safe,
induction of labour for suspected macrosomia was
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Figure 2
No further scans after 36 weeks
Maternal BMI, cervical
assessment at 41 weeks
Algorithm for antenatal management
of LGA pregnancy in non-diabetic
primiparous women. At all stages
of management, it is crucial to obtain
the woman’s agreement
BMI <30,
favourable cervix
BMI >30,
unfavourable cervix
Induction of labour
at 41+4 weeks
Consider elective
lower segment caesarean
section or induction of labour
Figure 3
Algorithm for antenatal management
of LGA pregnancy in non-diabetic
multiparous women. At all stages
of management, it is crucial to obtain
the woman’s agreement
No further scans after 36 weeks
Previous history of
macrosomia,vaginal delivery,
no birth injuries
Induction of labour
at 41+4 weeks
Previous
caesarean section
Previous vaginal
delivery or indication
for caesarean section
not failure to
advance; and/or
BMI <30
Vaginal birth
after caesarean
section
Box 1
First stage
Management in labour of women
with LGA pregnancy
Intravenous line, group and save
Continuous cardiotocograph monitoring
Adequate pain relief
Regular cervical assessment, especially of descent of the
presenting part
Timely augmentation with oxytocin if delay in the first stage
is diagnosed
Previous history
of shoulder dystocia
No previous vaginal
delivery; or previous
caesarean section
indicated by failure to
advance; and/or BMI
>30
Consider elective
lower segment
caesarean
section
Mild (no
brachial
plexus injury)
Severe (brachial
plexus injury)
Induction of
labour at 41+4
weeks and short
trial of labour
Elective lower
segment
caesarean
section
expectant management with labour induction in
women with suspected fetal macrosomia.Based
on data from nine observational studies,labour
induction for suspected fetal macrosomia results
in an increased caesarean delivery rate without
improving perinatal outcomes.However,two
randomised controlled trials have not confirmed these
findings,although their statistical power is limited.
Second stage
Early recourse to caesarean section if there is no descent
of the presenting part
Delivery by a senior midwife
Obstetric registrar or consultant in attendance
Third stage
Active management of third stage and administration of
Syntometrine® (Alliance) (ergometrine and oxytocin) by
injection
performed because it was thought to prevent
problems from severe cephalopelvic disproportion
and its associated maternal mortality and severe
morbidity. Nowadays, many obstetricians induce
labour at term when the fetus is estimated to be
either LGA or macrosomic.
A meta-analysis of systematic review on 11 studies by
Sanchez-Ramos et al.39 compared the outcomes of
254
Similarly, according to Irion and Boulvain,40
compared with expectant management, induction
of labour for suspected macrosomia in nondiabetic women has not been shown to reduce the
risk of caesarean section or instrumental delivery.
Perinatal morbidity (shoulder dystocia) was not
significantly different between groups.
Thus, current evidence shows no benefit of a policy
of routine induction of labour at the mere indication
of suspected fetal macrosomia (4000 g).
From the retrospective case-controlled study by
Ben-Haroush et al.,41 induction of labour for
suspected LGA fetuses increases the risk of
caesarean section, confirming the results of
previous studies. However, within the subgroup of
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multiparous women, caesarean section rates were
not increased, with no major maternal or fetal
complications, showing that nulliparity was
significantly and independently associated with
increased risk of caesarean section.
A holistic approach should be taken in the
management of pregnant women. Important
variables such as women’s age, height, BMI, parity,
birth weights of previous babies and obstetric
history, including previous shoulder dystocia and
cervical score, should be considered in the decisionmaking process.
Based on an analysis of treatment of suspected fetal
macrosomia,37 expectant treatment is the most
cost-effective approach. In a large cohort studied
by Walsh et al.,33 88% of women who laboured with
a macrosomic infant achieved vaginal delivery. If
expectant management is decided upon, the
woman should be fully informed about the benefits
and possible consequences, including care during
labour.
An observational study carried out by Draycott
et al.42 demonstrated that the introduction of
shoulder dystocia training for all maternity staff
was associated with improved management and
neonatal outcomes of births complicated by
shoulder dystocia.
During labour, regular assessment of progress is
required, especially of engagement, descent and
rotation of the fetal head. Continuous electronic
monitoring of the fetal heart rate should also be
performed because of the increased oxygen
requirement of the macrosomic fetus and the
association with prolonged labour. Thorough
second stage assessment is crucial if it is prolonged,
in order to avoid forceful extraction by
instrumental delivery. A competent obstetrician
must be in attendance to handle shoulder dystocia
promptly and effectively. Moreover, a paediatrician
should be present at the time of delivery, since
hypoxia and other injuries may be expected. Active
management of the third stage of labour should be
exercised to avoid postpartum haemorrhage.
Management of fetal
macrosomia in special
circumstances
Previous caesarean section
The medical literature does not support elective
caesarean section for suspected fetal macrosomia
in non-diabetic women and there appears to be
no reason for treating mothers with previous
caesarean sections differently.43
There is still a very low threshold for elective
caesarean section in non-diabetic pregnant women
© 2010 Royal College of Obstetricians and Gynaecologists
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with a birth weight of 4000 g. One in four nondiabetic pregnant women with a birth weight
4000 g underwent elective caesarean section with
the indication of ‘one previous caesarean section
with large for date’ in our institution (unpublished
retrospective audit from 1 January 2008 to 30 June
2009).
Strong predictors of success of vaginal delivery are:
previous vaginal birth, indication for previous
caesarean delivery and maternal BMI. Previous
vaginal birth predicted the success of trial of vaginal
births in women with macrosomic fetuses.43–46
'Failure to advance’ as an indication for previous
caesarean section seems to be associated with lower
success rates of trial of labour.46 Maternal obesity is
an independent risk factor for failed trial of labour
in women with previous caesarean sections.47
Previous shoulder dystocia
Women (with or without diabetes) with previous
shoulder dystocia have an increased risk of
recurrence, ranging from 1.1–16.7%.48,49 In
non-diabetic women, there is insufficient
evidence to support routine elective delivery;
however, the contrary applies to those cases
complicated by permanent brachial plexus
injury.50 A thorough review of previous delivery
records is necessary.
Shoulder dystocia seldom results in brachial plexus
injury. Most injuries are transient; half the cases of
shoulder dystocia occur in infants with birth
weights 4000 g and approximately one-third of
brachial plexus injuries are not even associated with
a clinical diagnosis of shoulder dystocia. As many as
50% of all brachial plexus injuries are attributable
to unavoidable intrapartum or antepartum
events.51 They can, therefore, occur through
mechanisms other than the efforts exerted to
reduce an impacted shoulder. This implies that the
mode of delivery does not have a major impact on
the incidence of injuries in about 40% of women
experiencing brachial plexus injury.52 In fact,
brachial plexus injury has been reported even after
caesarean delivery. Thus, caesarean delivery reduces
but does not eliminate the risk of birth trauma
associated with macrosomia.51
Conclusion
The widespread availability of obstetric ultrasound
and the fear of medico-legal action due to shoulder
dystocia have led obstetricians to consider
interventions for ultrasonographically diagnosed
macrosomia. We have found no evidence to
support a policy of induction of labour or routine
elective caesarean section of non-diabetic women
with ultrasonographically diagnosed LGA
pregnancies if the EFW is 5000 g. However, there
is evidence to support elective caesarean section
for women with EFW 5000 g.
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Management of clinically LGA non-diabetic
pregnancies should not rely solely on ultrasonic
measurements and there should be a holistic
approach complemented by clinical judgement,
including maternal body weight, past obstetric
history and clinical assessment.26 Moreover, prompt
assessment and management of shoulder dystocia
and preparation to maximise the efficiency of
shoulder dystocia manoeuvres are critical.
Acknowledgements
We thank Claire Coleman, Postgraduate Medical
Centre Librarian, Wycombe Hospital, for help
with the systematic literature search.
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