Clinical Research in the Management of Macrosomia/Big baby in non-diabetic mothers

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. This trend has been attributed to increases in maternal height ,body mass, gestational weight gain and diabetes, reduced maternal cigarette smoking; and changes in socio demographic factors.

It is known that there is an increase in maternal and neonatal morbidity associated with fetal macrosomia.

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. Birth weights 4000 g, 4200 g and 4500 g are used as definitions of newborn macrosomia.

Macrosomic infants are sub-classified into three groups:

Grade 1   4000-4499g

Grade 2   4500-4999g

Grade  3  > 5000g

Risk factors and obstetric complications associated with Macrosomia

Male infant, multiparity, maternal age 30–40 years, white race, diabetes and gestational age 41 weeks and previous macrosomic baby appeared to be associated risk factors. Women who delivered a macrosomic infant were more likely to undergo caesarean birth and to suffer shoulder dystocia, chorioamnionitis, fourth-degree perineal tear, postpartum haemorrhage and longer hospital stay.

The research/evidence showed no differences in adverse birth outcomes between birth weights of 3500–3999 g and those of 4000–4499 g. 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. The risk of shoulder dystocia rises from 1.4% for all vaginal deliveries to 9.2–24% for birth weights 4500 g.

Long-term health risks

The association between birth weight and risk of type 2 diabetes in later life showed a U-shaped association.Those with a high birth weight had a significantly increased risk of asthma during childhood, 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.

Diagnosis of Fetal Macrosomia

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 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.

To improve assessment of fetal growth, it is critical that the measurements are taken serially rather than done as a one-off measurement.

Ultrasonographic prediction of fetal macrosomia

Ultrasound measures used for predicting a macrosomic fetus are either single parameters(such as abdominal circumference or combinations of measurements to estimate fetal weight. Ultrasound biometry used to detect fetal weight 4000 g is characterized by low sensitivity, low positive predictive value and high negative predictive value.

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. 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.

Management on the basis of Research/Evidence

Management of pregnancies with suspected fetal macrosomia 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 tears. 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. Thus, elective caesarean section for the sole indication of macrosomia cannot be justified.

Clinical research, in conjunction with cost effectiveness 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.Labour induction for suspected fetal macrosomia results in an increased cesarean delivery rate without improving perinatal outcomes. Compared with expectant management, induction of labor for suspected macrosomia in non diabetic 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 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 research/ evidence shows no benefit of a policy of routine induction of labor at the mere indication of suspected fetal macrosomia (4000 g).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 decision making process.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 labor, 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 labor. 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 pediatrician should be present at the time of delivery, since hypoxia and other injuries may be expected. Active management of the third stage of labor should be exercised to avoid postpartum hemorrhage.

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.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. Failure to advance’ as an indication for previous caesarean section seems to be associated with lower success rates of trial of labor. Maternal obesity is an independent risk factor for failed trial of labor in women with previous caesarean sections.

Previous shoulder dystocia

Women (with or without diabetes) with previous shoulder dystocia have an increased risk of recurrence, ranging from 1.1–16.7%. 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. 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.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.

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 labor or routine elective caesarean section of non-diabetic women with ultrasonographically diagnosed LGA pregnancies. 

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. Moreover, prompt assessment and management of shoulder dystocia and preparation to maximize the efficiency of shoulder dystocia maneuvers are critical. The best plan of management should include an informed mother and well designed plan for obstetric emergencies.

Prevention of Macrosomia.

 The association between maternal weight, weight gain during pregnancy and macrosomia has led to a proposal that the optimization of maternal weight before pregnancy and limitation of weight gain during pregnancy would be useful strategies.

References:

?The Obstetrician and Gynecology

?High Risk pregnancies.

?Recent Advances in Ob/Gy.

RCOG Guidelines