Fetal Macrosomia

Aka: Fetal Macrosomia, Large for Gestational Age

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II. Definition

  1. Macrosomia
    1. Fetal weight 4500 grams (ranges from 4000-5000 grams)
  2. Large for Gestational Age
    1. Birth weight above 90th percentile

III. Risk Factors: Macrosomia

  1. Maternal Diabetes Mellitus or Glucose Intolerance
  2. Multiparity
  3. Prior history of macrosomic infant
  4. Post-Dates Gestation
  5. Maternal Obesity or excessive weight gain
  6. Male fetus
  7. Parental stature
  8. Genetic disorders
    1. Beckwith-Wiedemann Syndrome
    2. Sotos Syndrome

IV. Pathophysiology

  1. Fetal Growth
    1. Overgrowth
      1. Hallmark of Diabetes Mellitus
      2. No concurrent vascular disease present
    2. Intrauterine Growth Retardation
      1. Long standing Diabetes Mellitus
      2. Vascular Disease with decreased placental perfusion
  2. Control of Fetal Growth
    1. First half of pregnancy: Genetics
    2. Second half of pregnancy: Multifactorial
      1. Nutrients
      2. Oxygen
      3. Insulin as growth factor
  3. Selective Macrosomia
    1. Insulin sensitive tissue
      1. Heart
      2. Liver and Spleen
      3. Thymus
      4. Adrenal
      5. Subcutaneous fat
      6. Shoulders
    2. Insulin insensitive tissues
      1. Water content
      2. Brain Mass (relative to rest of body)

V. Signs: Classic infant of Diabetic Mother

  1. Gigantism
  2. Visceromegaly
  3. Plump, sleek liberally coated with vernix
  4. Full faced and plethoric

VI. Diagnosis

  1. Clinician's fetal weight estimate (Leopold's Maneuvers)
    1. Error in weight estimation: 300 grams
    2. More accurate than Obstetric Ultrasound estimate
    3. Estimate altered by physiologic characteristics
      1. Amniotic fluid volume
      2. Uterine Size and configuration
      3. Mother's body habitus
  2. Obstetric Ultrasound
    1. Error in weight estimation: 300 to 550 grams
    2. Estimated fetal weight and Abdominal circumference
    3. Correlates 88% with diagnosis of macrosomia

VII. Efficacy: Fetal Macrosomia prediction and prevention

  1. Cesarean delivery for fetal macrosmia indications
    1. ACOG recommends considering cesarean delivery for fetal weight >5000 g (11 lb)
    2. ACOG recommends considering cesarean delivery for Gestational Diabetes AND weight >4500 g (9 lb 15 oz)
    3. (2017) Obstet Gynecol 129(5): e123-33
  2. However, prior studies did not support early induction or Cesarean Section
    1. Elective Cesarean Section
      1. Analysis based on permanent Brachial Plexus Injury
      2. C/S for EFW 4500g prevents 1 case/3700 treated
      3. U.S. cost: $8.7 Million/case prevented
    2. Early induction
      1. Increases rate of Cesarean Section
      2. Does not favorably alter perinatal outcomes
      3. Sanchez-Ramos (2002) Obstet Gynecol 100:997-1002 [PubMed]
  3. Specific population targeting is also ineffective
    1. Vaginal Birth after Cesarean section
    2. Maternal Diabetes Mellitus
      1. Optimal Blood Glucose management is paramount
      2. Other intervention strategies are unproven
    3. Previous Shoulder Dystocia

VIII. Management

  1. Tight glycemic control
    1. Decreased Fetal Macrosomia
    2. Decreased Neonatal Hypoglycemia
    3. Decreased perinatal mortality
  2. Elective Cesarean Section (no support in literature)
    1. Indications per ACOG
      1. Estimated fetal weight > 4500 grams
    2. Possible Indications if Estimated fetal weight >4000g
      1. Pelvic architecture
      2. Prior Cesarean Section
      3. Prior Shoulder Dystocia
      4. Evidence of Cephalopelvic Disproportion
      5. History of poor progress of labor

IX. Complications

  1. Labor Dystocia
    1. Labor Augmentation needed
    2. Prolonged second stage
  2. Shoulder Dystocia
  3. Perinatal asphyxia
  4. Birth injury
  5. Respiratory distress syndrome
  6. Hypoglycemia

X. References

  1. Combs (1993) Obstet Gynecol 81:492-6 [PubMed]
  2. Rouse (1996) JAMA 276:1480-6 [PubMed]
  3. Weeks (1995) Am J Obstet Gynecol 173:1215-9 [PubMed]
  4. Zamorski (2001) Am Fam Physician 63(2):302-6 [PubMed]

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