Macrosomia Clinical Presentation
- Author: Allahyar Jazayeri, MD, PhD, FACOG, DACOG, FSMFM; Chief Editor: Christine Isaacs, MD more...
Fetal macrosomia has been defined in several ways. The definitions include birth weight greater than 4000-4500 g or greater than 90% for the newborn adjusted for race, sex, and gestational age. Based on these definitions, macrosomia occurs in 1-10% of all deliveries. Macrosomia may place the mother and fetus or neonate at risk for adverse outcomes. Antenatal risk factors reportedly predict macrosomia at birth. Identification of these at-risk pregnancies 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 one of the strongest risk factors 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. 
Maternal weight prior to pregnancy can affect the weight of the fetus. Women who are obese are more likely to have larger infants. [7, 8]
Excessive weight gain in pregnancy is a risk factor for macrosomia. The risk is greater for women with obesity than for women without obesity. 
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.  See the Gestational Age from Estimated Date of Delivery (EDD) calculator.
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.
Fetal sex influences macrosomic potential. Male infants weigh more than female infants at any gestational age. Recent studies have confirmed this association. 
Excessive amniotic fluid defined as greater than or equal to 60th percentile for gestational age has recently been associated with macrosomia. 
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.
Many physical examination findings help identify a pregnancy at risk for macrosomia.
Maternal obesity is associated with fetal macrosomia. Maternal body mass index (BMI) is a good way of diagnosing obesity prior to pregnancy. Calculated based on height in meters and weight in kilograms, BMI is determined using the following formula:
BMI = (weight [kg])/(height [m])2
Body fat percentage
Body fat percentage can be estimated using the following Deurenberg equation:
Body fat percentage = 1.2(BMI) + 0.23(age [y]) – 10.8(sex) – 5.4
Males are coded as 1 and females are coded as 0. This formula has a standard error of 4% and explains approximately 80% of the variation in body fat.
WHO criteria for BMI
The most widely accepted definition for obesity is that 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 published in 1990. The suggested weight gain is 11.2–15.9 kg (25–35 lb) for women with a normal BMI, 6.8 –11.2 kg (15–25 lb) for women who are overweight, and 6.8 kg (15 lb) for women who are obese. Excessive weight gain in pregnancy, especially in women who are already obese, is a risk factor for macrosomia.
Fundal height measurements
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. However, in general, a fundal height that is 3-4 cm larger than the gestational age of the pregnancy in the third trimester necessitates further testing to determine the cause. Excessive fetal growth can be one reason for the discrepancy between the fundal height and the gestational age of the pregnancy.
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%.[14, 15]
Causes for macrosomia include factors that contribute to excessive fetal growth and weight gain.
Diabetes that is poorly controlled in pregnancy is the greatest 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 insulinlike growth factor levels, which stimulate glycogen synthesis, fat deposition, and fetal growth.
Excessive maternal weight gain and/or prepregnancy weight also play the some role in macrosomia by providing excessive growth in selected cases. Whether this is also due to undiagnosed glucose intolerance in these individuals remains to be studied.
Genetic factors also contribute to fetal size. Taller and heavier parents typically produce larger offspring.
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