Medical Care
Induction of labor for presumed fetal macrosomia has in recent history been discouraged due to unclear benefit. However, in a randomized controlled trial (RCT) by Boulvain et al, 822 women with estimated fetal weight > 95th percentile at term were randomized to induction versus expectant management. Induction of labor was associated with reduced risk of shoulder dystocia; however, the study was underpowered to detect a difference in brachial plexus injury and none occurred in either group. In addition, induction of labor did not increase cesarean section rate as had been feared. A Cochrane systematic review of four RCTs that included 1190 patients examined outcomes with induction of labor for large for gestational age. [58] The Boulvain RCT contributed 800 of the 1190 patients and dominated the findings of the review. The review concluded that induction of labor in suspected fetal macrosomia does not reduce the risk of brachial plexus injury but does reduce birth weight, or the risk of skeletal injury and shoulder dystocia. [59]
Macrosomia is related to perinatal complications and the term fetus increases its body mass approximately 150-200g per week. Early term or 39-week induction of labor can reduce rates of macrosomia compared with expectant management, and therefore may decrease the complications of macrosomia.
A large retrospective cohort study using the U.S. Vital Statistics data that included singleton, non-anomalous deliveries at 37-39 weeks of gestation from 2011 to 2013 compared maternal and neonatal outcomes of appropriate weight for gestational age (AGA) infants versus large for gestational age (LGA) but non-macrosomic infants (< 4000 g). The study showed that LGA non-macrosomic birth weights were associated with increased composite maternal and neonatal morbidity compared with infants born with AGA growth. Maternal morbidity included maternal transfusion, ruptured uterus, unplanned hysterectomy, admission to intensive care unit, or unplanned procedure. Neonatal morbidity included Apgar score less than 5 at 5 minutes, assisted ventilation for more than 6 hours, seizure or serious neurologic dysfunction, significant birth injury, or neonatal mortality. [60]
Even though the risk of fetal and maternal morbidity increases with macrosomia, most deliveries of macrosomic infants are uncomplicated. The American College of Obstetricians and Gynecologists (ACOG) continues to recommend against delivery before 39 0/7 weeks unless medically indicated. Data remain inconclusive whether intervention is better than expectant management for suspected LGA fetuses. Therefore, induction of labor for suspected macrosomia before 39 0/7 weeks of gestation is not recommended by ACOG owing to insufficient evidence that reducing the risk of shoulder dystocia outweighs the risks associated with early delivery. [1]
Cesarean delivery to reduce the risk associated with macrosomia may place the mother at risk, and subsequent pregnancies are at risk of uterine dehiscence before or during the onset of labor. Not all cases of nerve injuries can be prevented by cesarean delivery because some occur in utero. Estimates indicate that as many as 3,695 cesarean deliveries in non-diabetic women and 443 cesarean deliveries in diabetic women must be performed to prevent a single permanent brachial plexus nerve injury in infants of estimated fetal weight greater than 4,500 g. [61] Expert opinion suggests that there may be some benefit to offering scheduled cesarean section to mothers with suspected macrosomia (>5000 g in non-diabetic mothers and >4500 g in diabetic mothers); however, the decision to perform cesarean section for macrosomia is left to the provider and patient. [1]
Decision making regarding delivery should be individualized to the patient, taking into account risks and benefits of both macrosomia and other delivery factors such as surgical risks, including implications for future childbearing, and the neonatal risks of early term delivery.
Surgical Care
The obstetrician involved in the care of a macrosomic infant must be familiar with procedures that release a shoulder dystocia at delivery. See the Medscape topic Shoulder Dystocia for more information.
Because macrosomic infants are at increased risk of cesarean delivery the provider must be capable of performing a cesarean delivery or must have backup help available in case cesarean delivery is necessary.
Operative vaginal deliveries (eg, forceps, vacuum) must be performed with caution in infants with risk factors for macrosomia. Midpelvic procedures are associated with a much greater risk of significant shoulder dystocia (50%) in macrosomic infants than non-macrosomic infants. [62]
Consultations
In patients with poorly controlled diabetes resulting in macrosomia, consultation with a maternal fetal medicine specialist to obtain better control may be useful.
In cases of significant macrosomia (estimated fetal weight >99th percentile), a careful evaluation of the dates and a sonographic evaluation of fetal anatomy can be helpful to investigate potential causes of the macrosomia. Incorrect gestational age is frequently encountered and may result in estimated fetal weights that are greater than the 90th percentile but usually should not result in estimations greater than 4000 or 4500 grams. Intra-abdominal and intracranial masses may result in larger abdomen and head measurements resulting in a large estimated fetal weight. Such causes should be diagnosed prior to delivery if at all possible.
Diet
Pre-gestational obesity and excessive gestational weight gain in pregnancy are two of the strongest predictors of macrosomia at birth; therefore, a possible intervention to prevent macrosomia may be nutrition education and an exercise program. Excessive maternal weight gain can double the risk of macrosomia; thus, a reasonable suggestion is careful weight control for women who exceed the recommended weight gain in pregnancy. [10, 36, 43] Gestational weight gain is a modifiable risk factor. [36] Intuitively, this type of intervention, if successful, may reduce the risks of macrosomia in those women who are obese prior to pregnancy or who may gain excessive weight in pregnancy. In diabetic patients, maternal diet alone, without the use of insulin, did not alter rates of macrosomia. [63, 64]
A systematic review that included 18 RCTs with 1151 women revealed that dietary changes/interventions resulted in a greater decrease in fasting and postprandial glucose values and a lower need for medication treatment for gestational diabetes. Dietary interventions were also shown to be associated with lower birth weight and lower rates of macrosomia (relative risk, 0.49 [95% CI, 0.27-0.88]; P =.02). [65]
A multi-center RCT by Landon et al assessed 958 women with mild gestational diabetes and randomized them to usual prenatal care vs diet and lifestyle intervention with treatment as medically indicated for glycemic control. The study found a statistically significant difference in the control group vs treatment group in the frequency of large-for-gestational-age infants, 14.5% vs 7.1%, as well as reduced frequency of shoulder dystocia (4.0% vs 1.5%) and birth weight over 4000 g (14.3% v 5.9%). [44]
One study randomized 98 women with gestational diabetes mellitus and fetal abdominal circumference of >75% for gestational age to either diet alone or diet and twice-daily insulin. Insulin along with diet decreased the risk of birth weight > 90th percentile from 45% in those treated with diet alone to 13% in those treated with diet and insulin (P< .01). [63]
Dietary and weight gain guideline education should be provided for obese patients of patients experiencing excessive gestational weight gain as these are associated with macrosomia, gestational diabetes, cesarean delivery, and preeclampsia. Such intervention may potentially reduce maternal and neonatal risks. At the present time, clinical trials are lacking support of the effectiveness of such intervention. [66]
Activity
ACOG recommends that women without any contraindications should be encouraged to participate in aerobic and strength conditioning exercises during pregnancy to reduce the risk of macrosomia. [1] The U.S. Department of Health and Human Services Physical Activity Guidelines for Americans recommends at least 150 minutes of moderate intensity aerobic exercise per week during pregnancy and postpartum. [67] Despite these recommendations, only 9-15% of pregnant women meet this guidelines. [68]
A systematic review that included 135 studies revealed that prenatal exercise is safe and beneficial for the fetus, with decreased rates of macrosomia without an increase in neonatal complications or adverse childhood outcomes. [68] Another meta-analysis that included RCTs comparing standard care with standard care plus supervised prenatal exercise revealed that prenatal exercise reduced the risk of having a LGA infant (greater than 4000 g or greater than 90th percentile for gestational age) without increasing the risk of having a small for gestational age (SGA) infant (odds ratio, 0.69; 95% CI, 0.55-0.86). Maternal gestational weight gain and odds of cesarean delivery were also decreased in the group that had supervised prenatal exercise. [69]
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Photograph of a macrosomic newborn soon after birth.
