Fetal macrosomia: a problem in need of a policy

Fetal macrosomia is associated with increased risks for the mother, including emergency Cesarean section (CS), instrumental delivery, shoulder dystocia and trauma to the birth canal, bladder, perineum and anal sphincter; for the baby, complications include increased mortality, brachial plexus or facial nerve injuries, fractures of the humerus or clavicle and birth asphyxia1-7. Fetal macrosomia now is usually defined as a neonate with a birth weight above 4.5 kg2-4 and has a prevalence in developed countries of 1.3–1.5% of all births. A gestational-age-dependent definition, the 97th centile, is sometimes used and has a similar prevalence. Other definitions, such as birth weight > 4 kg (prevalence, 7%) or birth weight > 90th centile5, include many babies with a lower order of risk for adverse outcome. The 4.5-kg limit is only appropriate for term births and can be criticized for being rather arbitrary; for example, the incidence of shoulder dystocia rises steeply between birth weights of 4.0 and 4.25 kg6, so 4.25 kg could legitimately be used as the cut-off. However, the 4.5-kg limit defines unequivocally a high-risk group of babies that requires accurate diagnosis and intelligent management to minimize the risks to mother and baby. Fetuses growing above the 97th centile during the third trimester can also be regarded as macrosomic, but, although at increased risk from metabolic problems7, they do not contribute significantly to the classical injuries associated with fetal macrosomia until term is reached. Three per cent of all births and 5–10% of macrosomic fetuses8 are associated with maternal diabetes and the management of this subset will not be discussed in detail in this Editorial. Women with diabetes or gestational diabetes are usually identified prenatally and monitored and cared for by a specialist team. Induction of labor and elective CS is recommended according to individual circumstances2. Macrosomic fetuses of non-diabetic women can be identified as being at risk by factors such as maternal obesity and family history but are generally unsuspected until the possibility of a big baby is raised by antenatal clinical or ultrasound examination. Management of this group of pregnant women has been determined largely by two influential publications. In the first, Rouse et al.9 performed a decision analysis on the monetary costs of three different management policies, i.e. management without ultrasound; ultrasound and elective CS delivery for a predicted birth weight of 4.0 kg; and ultrasound and CS delivery for a predicted birth weight of 4.5 kg. On the basis of an ultrasound sensitivity of 60% and specificity of 90% for prediction of a macrosomic fetus, they calculated that in the USA the 4.5-kg management policy would entail carrying out 3695 CSs or spending an extra 8.7 million dollars for each brachial plexus injury prevented in non-diabetic gestations. Their conclusion was that, ‘for the 97% of women who are non-diabetic, elective CS for ultrasonically diagnosed macrosomia was economically unsound.’ This study was quoted extensively in the second influential publication, the American College of Obstetricians and Gynecologists (ACOG) Practice Bulletin2, which provided a detailed quantification of the risks of macrosomia and recommended clinical management when ultrasound predicted this condition. The ACOG concluded that although the diagnosis of fetal macrosomia was imprecise, prophylactic CS ‘may be considered’ for suspected fetal macrosomia with estimated fetal weights (EFW) ≥ 5.0 kg (i.e. 11 pounds) in women without diabetes. The implication, of course, is that for weights < 5.0 kg, elective CS should not be considered. This recommendation has since been echoed by several authors8, 10, 11. In the UK, the Royal College of Obstetricians and Gynaecologists (RCOG), in its Shoulder Dystocia Guideline in 201212, refers to the Rouse paper findings and notes the ACOG recommendations, but does not provide any management guidelines for suspected macrosomia in non-diabetic women. However, as the RCOG/National Institute for Health and Care Excellence (NICE) guidelines on antenatal care (2012)13 stipulate that ‘Ultrasound estimation of fetal size for suspected large for gestational age unborn babies should not be undertaken in a low risk population’ and the RCOG/NICE guideline on CS14 does not list fetal macrosomia amongst the indications for elective CS, the view of RCOG/NICE on this subject is clear: elective CS should not be performed for this indication. Thus, while it is universally accepted that elective CS can virtually eliminate shoulder dystocia and brachial plexus injury without increasing maternal mortality, the current mantra is that ultrasound prediction of macrosomia is inaccurate and brachial plexus injuries are rarely permanent, so justification fails both on clinical and on monetary grounds. However, as the ACOG and RCOG recommend elective CS in women with diabetes with a predicted birth weight > 4.5 kg, they appear to be acknowledging tacitly that ultrasound estimates of birth weight are not valueless. The findings of the Rouse paper have been challenged recently by Culligan et al.4, who carried out a similar decision analysis comparing current ‘standard care’ with an ultrasound scan at 39 weeks and elective CS for predicted birth weight ≥ 4.5 kg. This analysis included new longitudinal data on brachial plexus injury to the newborn and also risks of maternal anal and urinary incontinence. Their outcome measures included the number of brachial injuries and cases of incontinence averted, incremental monetary costs per 100 000 deliveries, expected quality of life of the mother and child and the ‘quality adjusted years’ (QUALY) associated with each of the two policies. They conclude that a policy whereby primigravid patients in the USA have a 39-week scan to estimate fetal weight followed by elective CS for predicted birth weights ≥ 4.5 kg was cost effective. This paper has had minimal impact on public health care policy, perhaps because it was published in a urogynecological journal. This Editorial will examine the issues surrounding the debate over elective CS for fetal macrosomia and make suggestions for a policy fit for the 21st century. Published graphs of neonatal mortality against birth weight show a sharp rise in babies > 4.5 kg15, 16. While this may in part be due to the association of macrosomia with post-dates gestations and maternal diabetes, it also reflects the high rate of emergency CS and instrumental delivery and subsequent birth trauma in women who labor with a large fetus. For babies weighing 4.5 kg or more, the emergency CS rate is 45%9 and the instrumental delivery rate 19%17. Long-term damage to the infant is most commonly discussed in relation to shoulder dystocia. The average risk of shoulder dystocia in the obstetric population is 1.4%, but when birth weight is greater than 4500 g the risk varies from 9 to 24%2. The large study from California6, which included 6238 infants with shoulder dystocia, put the risk at 14.3% for non-diabetic infants weighing between 4500 and 4750 g and 21.1% for infants weighing 4750–5000 g. The incidence of shoulder dystocia in vacuum- or forceps-assisted births was 23% for infants with birth weight between 4500 and 4750 g and 29% for those between 4750 and 5000 g. Similar findings were reported by Acker et al.18. Rates of shoulder dystocia in mid-forceps deliveries of infants heavier than 4500 g have been reported to be above 50%2, so, barring extreme emergencies, CS delivery should be performed for mid-pelvic arrest of the fetus with suspected macrosomia. Induction of labor is associated with a doubling of the risk of CS delivery without reducing the risk of shoulder dystocia19, 20. Obstetric brachial palsy injury (OBPI) is strongly associated with macrosomia and shoulder dystocia. The average rate of OBPI in the obstetric population is 0.5–1.9/1000, while for babies with a birth weight > 4.5 kg there is an 18–21-fold increased risk2. Macrosomic compared with non-macrosomic infants delivered after shoulder dystocia are at a higher risk of OBPI. Rouse et al.9, in their analysis, estimated that 26% of babies with birth weights ≥ 4.5 kg delivered following shoulder dystocia will have a brachial plexus injury. Overall, the risk of OBPI for macrosomic infants delivered vaginally is 4–8%2. Raio et al.21 stressed the importance of short maternal stature as an associated risk factor in predicting birth injury. They calculated that the number of CS deliveries required to prevent a single case of permanent OBPI in fetuses predicted to be ≥ 4.5 kg would be 30 in women shorter than 155 cm and 715 in those taller than 180 cm. Gudmundsson et al.22 confirmed this and constructed risk estimation curves based on birth weight and maternal height. The risk of permanent injury is frequently reported to be about 10% among all cases of OBPI2 and Rouse et al.9 estimated for their cost analysis that the risk of permanent injury from OBPI was only 6.7%. Most of these estimates were based on short-term follow-up and few gave details of the pediatric examinations. Subsequent to the Rouse paper, two substantial longitudinal studies, each of over 60 infants with OBPI carried out in orthopedic surgery and rehabilitative medicine departments, were published. Waters23, in an extremely detailed study, found that only 16.7% of OBPI cases spontaneously resolved, 27% were permanent and severe (arm useless throughout life) and 56% were permanent and moderate (abduction and rotation limited to < 30°). Hoeksma et al.24 reported that only 51% of OBPI children underwent complete recovery because shoulder contractures with functional deterioration developed in 30% of infants who had apparently made a full neurological recovery. It should also be noted that persistent OBPI is six times more common when the birth weight is ≥ 4.0 kg compared with < 4.0 kg6. Culligan et al.4 in his cost analysis factored in the data from the Waters study. More serious are the other problems associated with the birth of a large baby. The California study6 found that birth injuries in general as well as birth asphyxia were significantly more frequent in infants born following labors complicated by shoulder dystocia. There was also an association between neonatal length of stay and ‘non-normal’ neonate at discharge. Iffy et al.25 studied retrospectively 316 fetal neurological injuries associated with arrest of the shoulders, across the USA. He found that as many as 64 (20%) children displayed manifestations of central nervous system (CNS) damage, such as cerebral palsy, seizures and cognitive defects, 6 or more months after their birth. They estimated that the risk of irreversible fetal damage in cases of attempted vaginal delivery exceeds 2.5% for fetuses ≥ 4.5 kg and 5% for birth weights above 5 kg. It should be noted that these asphyxia problems were only recorded in association with shoulder dystocia. The overall risk of CNS problems associated with macrosomia is likely to be higher. There is a strong correlation between macrosomia and damage and the of anal and urinary incontinence and weight > 4 kg risk of and due to labor and delivery, instrumental birth is incontinence a and vaginal delivery is now as its Three large found that macrosomia was a strong risk factor for anal The other factor was vaginal delivery, with after delivery of the shoulder dystocia more common in macrosomic infants may contribute to and anal There is a strong association between anal injury and maternal incontinence. A of in which was performed after vaginal birth found a incidence of anal defects, third of which were Culligan et al.4 calculated the of anal incontinence following or anal to be but this high and a of is more incontinence has a on and and is associated with A large baby is also likely to the of the and a injury to the and to vaginal et followed over a women for a longitudinal study after with elective CS delivery, vaginal birth was associated with a significantly greater of incontinence and to or the vaginal delivery significantly increased the for urinary incontinence anal incontinence and was was that CS was when performed in labor to complete birth to incontinence and functional length are following vaginal delivery, but this does not after The association between a large fetus, second and nerve damage has also been et in a follow-up study of found urinary incontinence at 6 months of 10% following CS, following vaginal delivery and following CS at any was et in a study, found that was to birth and In a follow-up and reported a prevalence of of 5 after et they found CS birth to significantly the risk of et found similar with of women after vaginal birth but only following In there is a strong between the delivery of a macrosomic fetus, instrumental delivery, anal and the of anal and urinary incontinence and is also is that most of the serious for both child and mother are to vaginal birth and that CS at any of labor to full is largely for these this it has to be the to a delivery when a decision to CS would these It is likely that the current management of the suspected macrosomic fetus would be different a of fetal weight were It is not that ultrasound is than clinical or the estimation of the weight of There is that ultrasound is to all other at the of the the of ultrasound is the only with which to pregnant women for fetal macrosomia. The is to put the of and length a which A few of the that are used the the by and a few the of the has a of 100 which that weight in for fetuses appear to be more many have found ultrasound prediction of macrosomia to be inaccurate and of clinical There are two to in ultrasound i.e. the which is on the of the prediction and the which is on the of the and can be by and fetal and that the of the fetal have been Other factors that are maternal and an In analysis of 11 different it is that the of the are to the for fetuses but most the weight of large and the weight of is also from analysis is that the for large fetuses is than that for or with findings were confirmed by et who compared different on fetal weight of birth. For fetuses ≥ 4.5 kg, the was 10% or in with an overall of The of birth weights in this was The that a of the of the by for the study population could have the in the macrosomic This it to have a for fetuses over 4.5 kg, to to a Most fetal weight prediction for macrosomia 4 kg and above as the of macrosomia or such as women with diabetes or who are the of the by Rouse et al.9, a high is to costs from for the age infant is to be it be a to a i.e. a scan at to a high-risk followed by a detailed scan at 39 weeks in those identified as being The of the or scan would be to as high a sensitivity as so that most large fetuses are in the The of the second scan would be to a high so that the would that of a fetus weighing more than 4.5 kg are The 39-week scan being performed on a high-risk population with a higher prevalence of large fetuses would be more likely to a for macrosomia and the ultrasound or were the of is that the of size limit the of that can be so the current is to include the of a short rather than a in the For example, recently et used a of fetal and and of fetal and to the weight of and ultrasonically For fetuses > 4.5 kg the at a of they were to of macrosomic fetuses for a rate of This was an on for the prediction of macrosomia. the it is a as are made but, with the of may to the of weight is to to shoulder dystocia on the that it is more likely to in fetuses with large This is of the fetus of the A paper in this of the this although and had and an > had a high of for predicting shoulder dystocia. of the scan would be to provide an to and women with and any problems associated with The scan would also an in which is also associated with at the other of the any have found to be as accurate as more for predicting fetal weight or While would be the of the in For example, in a study from a care performed between and weeks the of two of cases of macrosomic fetuses with a of all the had been performed after 30 the would likely have have reported that is in the large fetus in the third although many have used a birth weight of 4 kg as the of macrosomia. et found that with between 30 and weeks identified of babies with birth weight over 4 kg for a rate of A full with only a in the et a reported specificity and of in an population at a of as the they a sensitivity of and specificity of for the prediction of birth weight > 4.5 kg. the was only it is likely that this would rise the 27% of women identified as high risk were at 39 The and by Rouse et al.9 and Culligan et al.4 to their decision were but were based on of or post-dates gestations or babies with birth weights over 4 kg, and are not to the of an population to birth weights over 4.5 kg. Rouse et al.9 a low for ultrasound and calculated the cost of a of CSs to It should be that most show that ultrasound the birth weight of macrosomic the were with of 10% for all would be between 4 and 5 kg. Shoulder dystocia rises between 4 and 4.5 kg which that an would a high-risk This is not so for fetal weight for a birth weight many fetuses would be included in the ultrasound In ultrasound of fetal weight to although imprecise, are not valueless. It a and a of the of the and the importance of as accurate as factors the delivery of the macrosomic fetus, it is in relation to maternal and birth in the of this there was an debate in the as to elective CS should be performed at a in the of an obstetric indication. is is that there was that elective CS and vaginal birth were in of mortality for the mother, but that both had different of of which should be made In a quoted a to they or their would elective CS or vaginal delivery they had a with at The rate was Overall, CS, with of this over vaginal the for elective CS was of term of vaginal incontinence and anal damage, of damage from vaginal birth and its on and of damage to the baby. A in for of CS with greater on individual in decision has for a to to women on they should birth. the should be on of the of vaginal CS The of CS in women made of such will be more appropriate than any of the current The in published a in a the of would to the of elective CS delivery in a after were challenged in by and who that the of elective CS as a ‘may be by their to the complications of Their to a CS delivery on maternal included to a a second and a of and in a with the which be for a similar USA confirmed a high for maternal among American urinary and anal incontinence and for fetal or injury as A in found that of of of and of the of elective is to this Editorial is that when in the were with the that the baby was in but the was > 4.5 kg, of and 60% of elective that had from to in of elective CS for their when of the that the fetus was The paper with the this of should the of elective CS delivery be to all suspected fetal macrosomia are not with a but with in which the predicted weight of the fetus is 4.5 kg or with this most would elective CS for or their so it is that any with this would not his on the risks of vaginal birth associated with macrosomia and at a of elective Most women a vaginal birth. et reported that only of women in their of women an elective CS, but women about the risks of birth injury and to their their baby is at the of on the when is is a big baby. the of the mother will be a vaginal birth and it will be to the to provide the of risks so that and can make an about the of The risks of elective CS, such as neonatal CS and which part of the over maternal for CS, when the risks of vaginal birth with a macrosomic fetus are now on the other of the The maternal mortality rate with elective CS in a in is now as being greater than that of vaginal although data are not as the RCOG in their maternal mortality is virtually to the fetal and maternal for most of the to make a CS at any of labor is of most of the serious to mother and child that as a of shoulder dystocia, instrumental delivery and vaginal The that be is this is do these injuries to Shoulder dystocia can at the of a but this is more likely when it is associated with a baby. the current on to the number of CSs performed be a is it that the of the labor is not to fetal macrosomia does not that elective CS is the of although it should be made to the that elective CS is the is is that each and should be of the risks associated with a macrosomic fetus and shoulder dystocia. The of ultrasound should be part of the as well as the of CS in labor on both and fetal that will the elective CS will be a maternal and other risk factors such as age over 30 and history of A with a over cm has a significantly lower of shoulder dystocia and of labor be should be on the they have there is to the the It is that the in the decision they This is a in which maternal is Fetal macrosomia should be defined as a birth weight ≥ 4.5 kg. It is a high-risk which should be as by as ACOG in their appear to be in with this The cost analysis by Rouse et al.9, on which they does not factor in data on of asphyxia and maternal and it is in many of its The cost analysis by Culligan et al.4 is although of their can be that the risk of anal incontinence has been but has been made for the costs associated with birth which is a of shoulder dystocia. There in the cost estimates based on to to be that elective CS at 39 weeks in with an ultrasound > 4.5 kg is of the possibility of macrosomia should at the antenatal is a risk factor and a > 30 should of a is also associated with maternal weight of the is the to management and of Obstetricians and be as of the of a large fetus as of a is imprecise, but it is than other in predicting fetal macrosomia. performed over 90% of ultrasound of birth weight ≥ 4.5 kg will be over 4 kg and this will a group at high risk for emergency CS, vaginal delivery and maternal and fetal fetal macrosomia ultrasound of fetal size macrosomia in the third A scan between and with a scan at 39 has to a diagnosis of fetal macrosomia is the mother and be made of the risks of vaginal birth and be to elective CS or of labor without Induction of labor is as it the risk of shoulder dystocia. all cases of predicted fetal macrosomia is so that the in the labor will recommend CS there is any in or arrest of rotation or CS should also be the an fetal of the will prevent of from anal and incontinence and of a birth will prevent fetal trauma and from brachial plexus injury and fetal the are not in for CS are in and