Macrosomia Clinical Presentation

Updated: Feb 03, 2017
  • Author: Anna R Baur, MD; Chief Editor: Christine Isaacs, MD  more...
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Fetal macrosomia has been defined to include birth weight greater than 4000g or greater than 4500 g. [1] Macrosomia may place the mother and fetus or neonate at risk for adverse outcomes. Identification of pregnancies with antenatal risk factors for macrosomia may allow intervention to reduce the risk, to provide appropriate counseling, and to implement appropriate plans for monitoring and follow-up care during pregnancy and after delivery.

Note the following:

  • Maternal diabetes is a strong risk factor associated with giving birth to an infant that is considered large for gestational age. Pregestational and gestational diabetes result in fetal macrosomia in as many as 50% of pregnancies complicated by gestational diabetes and in 40% of those complicated by type 1 diabetes mellitus. Studies of macrosomic infants of diabetic mothers reveal a greater amount of total body fat, thicker upper-extremity skin fold measurements, and smaller ratios of head to abdominal circumference than macrosomic infants of nondiabetic mothers. [5]

  • Maternal weight prior to pregnancy can affect the weight of the fetus. Women who are obese are more likely to have larger infants. [19, 20, 3]

  • Excessive weight gain in pregnancy is a risk factor for macrosomia. The risk is greater for women with obesity than for women without obesity. [19, 3]

  • Gestational age is associated with macrosomia. Birth weight increases as gestational age increases. Prolonged pregnancies (>41 wk) are associated with an increased incidence of macrosomia. Macrosomic infants account for about 1% of term deliveries and 3-10% of postterm deliveries. [5] See the Gestational Age from Estimated Date of Delivery (EDD) calculator.

  • Multiparity and grand multiparity increase the risk of macrosomia. [21] Parity has been reported to be associated with 100-150 grams of weight gain at birth. [22]

  • A history of macrosomia can influence future pregnancies. Women who previously delivered a macrosomic fetus are 5-10 times more likely than women without such a history to deliver a baby considered large for gestational age the next time they become pregnant. [23]

  • Fetal sex influences macrosomic potential. Male infants weigh more than female infants at any gestational age. Recent studies have confirmed this association. [24, 15]

  • Excessive amniotic fluid defined as greater than or equal to 60th percentile for gestational age has recently been associated with macrosomia. [25]

  • Despite these so-called risk factors for macrosomia, much of the variation in birth weights remains unexplained. Most infants who weigh more than 4500 g have no identifiable risk factors. Kim et al found that 46.8 - 61.0% of the mothers with macrosomic infants assessed in their study had none of the three primary risk factors studied, which included maternal overweight, excessive gestational weight gain and GDM. [3]



Many physical examination findings help identify a pregnancy at risk for macrosomia.

Maternal obesity

Maternal obesity is associated with fetal macrosomia. [20] Maternal body mass index (BMI) is a good way of diagnosing obesity prior to pregnancy. The most widely accepted definition for obesity is based on the World Health Organization (WHO) criteria, which uses the BMI. Under this convention for adults, grade 1 overweight (commonly and simply called overweight) is a BMI of 25-29.9 kg/m2. Grade 2 overweight (commonly called obesity) is a BMI of 30-39.9 kg/m2. Grade 3 overweight (commonly called severe or morbid obesity) is a BMI greater than or equal to 40 kg/m2.

A BMI greater than 30 kg/m2 is associated with larger infants at delivery.

Pregnancy weight gain

The recommendations for weight gain in pregnancy have been based on the Institute of Medicine (IOM) guidelines which were updated in 2009. The suggested weight gain is 28-40lbs for BMI < 18.5, 25-35 lbs for BMI 18.5 – 24.9, 15-25 lbs for BMI 25.0-29.9, and 11-20 lbs for BMI > or = 30.0. [16]

Fundal height measurements and Leopold maneuvers

Fundal height measurements are an inaccurate way of estimating fetal size. They are influenced by maternal size, the amount of amniotic fluid, the status of the bladder, the presence of pelvic masses (eg, fibroids), fetal position, and many other factors. 

Leopold maneuvers are techniques developed to determine fetal presentation, lie, and size. They are also limited by many factors, as mentioned previously for fundal height measurements. However, these maneuvers provide the clinician with a general appreciation of fetal size and other important information. Prospective studies designed to evaluate Leopold maneuvers with fundal height measurement for the prenatal diagnosis of possible macrosomia report sensitivities of 10-43%, specificities of 99-99.8%, and positive predictive values of 28-53%. [26, 27] However, discrepancy between fundal height and estimated gestation age is often used to screen women for referral for evaluation of possible large for gestational age fetus by growth ultrasound.



Causes for macrosomia include factors that contribute to excessive fetal growth and weight gain.

There are numerous contributors to macrosomia, many of which are assessed in a case-control study by Okun et al, which list factors including: prior macrosomic infant, maternal prepregnancy weight, excessive gestational weight gain, multiparity, male fetus, gestational age >40 weeks, ethnicity, maternal birth weight, maternal height, maternal age younger than 17 years, and a positive 50g glucose screen with a normal 100g glucose tolerance test, in descending order of effect according to their analysis of data from 1000 deliveries of macrosomic and non-macrosomic infants in Edmonton, Alberta. [4]

A study done by Kim et al reviewed vital records between 2004 and 2008 in the state of Florida to assess the association between maternal BMI, maternal weight gain, and gestational diabetes mellitus with fetal macrosomia. They found that excessive maternal weight gain had the strongest association for a large for gestational age infant of the examined variables.  BMI of greater than 25 and gestational diabetes were also associated with having LGA infant. Initial BMI and gestational weight gain are also both modifiable risk factors and provide potential interventions to decrease a patient’s risk of having a macrosomic infant. [3]

Poor glycemic control in pregnancy is a major risk factor for fetal macrosomia. This is believed to be partially explained by excessive growth due to elevated maternal plasma glucose levels and resulting elevated insulin and insulin-like growth factor levels, which stimulate glycogen synthesis, fat deposition, and fetal growth.

Genetic factors also contribute to fetal size. Taller and heavier parents typically produce larger offspring.




Morbidity and mortality associated with macrosomia can be divided into maternal, fetal, and neonatal categories.

Maternal morbidity

Macrosomia is associated with a higher incidence of cesarean delivery (double that of control subjects) and with birth canal lacerations associated with vaginal delivery. Mulik et al reviewed the outcomes of 8617 deliveries over a period of 11 years. [14] In that population, 666 neonates were born with a birth weight of 4000-4499 g and 97 neonates were larger than 4500 g. In their study, Mulik et al found maternal morbidity to be associated with a birthweight of 4500 g or higher compared with a birth weight of less than 4000 g. Postpartum hemorrhage occurred in 3.1% of mothers with newborns weighing 4500 g or more compared with 1.5% in mothers with newborns weighing less than 4000 g. Blood transfusions occurred in 15.4% of mothers with newborns weighing 4500 g or more compared with 3.1% in mothers with newborns weighing less than 4000 g.

Neonatal morbidity

Macrosomic neonates are at risk for shoulder dystocia and birth trauma. This risk is directly related to neonatal birth weight and begins to increase substantially when birth weight exceeds 4500 g and particularly when it exceeds 5000 g. [6] Brachial plexus injury is rare, with an incidence of fewer than two cases per 1000 vaginal deliveries. This risk is approximately 20 times higher when the birth weight is more than 4500 g. [12] Mulik et al reported a higher incidence of NICU admissions for neonates with a birth weight higher than 4500 g compared with newborns with a birth weight of less than 4000 g (9.3% vs 2.7%). Risk of shoulder dystocia was 10 times higher in the larger babies (4.1% vs 0.4%).

In a large study by Raio et al, 3356 newborns who weighed more than 4500 g at birth were studied. Shoulder dystocia occurred in 310 of the newborns, and brachial plexus injuries occurred in 94 of the newborns (about 10% and 3%, respectively). In this population, gestational diabetes increased the risk of shoulder dystocia by a factor of two, while preexisting diabetes increased the risk four-fold. [28]

Fetal morbidity/mortality

Modestin et al investigated the effects of birth weight on fetal mortality and demonstrated that higher fetal mortality rates are associated with a birth weight of greater than 4250 g in nondiabetic mothers and a birth weight of 4000 g in diabetic mothers. [13] Stillbirth rates in macrosomic infants are twice as high as those in control subjects, irrespective of diabetes. However, for a birth weight of 4500-5000 g, the fetal death rate is fewer than two deaths per 1000 births for nondiabetic women and is approximately eight deaths per 1000 births for diabetic women. For a birth weight of 5000-5500 g, this rate is five to 18 deaths per 1000 births for nondiabetic women and is approximately 40 deaths per 1000 births for diabetic women. [13]

A retrospective cohort analysis designed to demonstrate the link between SGA and perinatal demise showed a “reverse J-shaped relationship” between birth weight percentile and risk of fetal and neonatal death. This means that the greatest risk of perinatal death is at birth weights < /= 3rd percentile and >/= 98th percentile. A great deal of research and management guidance has gone into surveillance for SGA infants, and this study would suggest that more investigation is warranted to examine the perinatal risks and optimal surveillance of the fetus with accelerated growth. [29]

This is supported by a study by Boulet et al that showed increased risk of neonatal death with increasing birth weight, most notable and statistically significant for infants with birth weights greater than 5000 g, or “grade 3 macrosomia” according to the model in their study. [6]