Large for Gestational Age (LGA): Definition and Implications
Large for gestational age (LGA) refers to a fetus or newborn whose estimated weight or birth weight exceeds the 90th percentile for the corresponding gestational age. This classification is based on population-specific growth charts that account for gestational age and often gender 1.
Diagnostic Criteria
LGA is determined through:
- Prenatal assessment: Ultrasonographic estimation of fetal weight (EFW) above the 90th percentile for gestational age 1
- Postnatal assessment: Birth weight above the 90th percentile for gestational age 1
The accuracy of LGA diagnosis depends on:
- Precise pregnancy dating (ideally using first-trimester crown-rump length measurements) 1
- Standardized fetal biometry measurements (biparietal diameter, head circumference, abdominal circumference, and femur length) 1
- Appropriate growth charts that reflect the population being evaluated 1
Clinical Significance
LGA status carries significant implications for both maternal and fetal/neonatal outcomes:
Maternal Risks
- Increased likelihood of cesarean delivery (adjusted OR = 1.98,95% CI = 1.10-3.55) 2
- Higher rates of instrumental deliveries 2
- Greater risk of postpartum hemorrhage 2
- Increased incidence of vaginal lacerations 3
Fetal/Neonatal Risks
- Shoulder dystocia during vaginal delivery 3
- Clavicle fractures and brachial plexus injuries 3
- Increased need for resuscitation (adjusted OR = 2.52,95% CI = 1.33-4.79) 2
- Higher rates of admission to neonatal intensive care units (adjusted OR = 3.76,95% CI = 1.89-7.49) 2
- Long-term risks of childhood obesity and metabolic disorders 3
Risk Factors for LGA
Several maternal factors increase the likelihood of LGA births:
- Pre-pregnancy obesity (strongest modifiable risk factor, adjusted OR = 2.73,95% CI = 1.49-5.01) 2
- Gestational diabetes mellitus (GDM) (increases risk 2.44-fold) 4
- Previous pregnancy (adjusted OR = 2.03,95% CI = 1.08-3.81) 2
- Maternal marital status (married mothers have adjusted OR = 1.85,95% CI = 1.00-3.42) 2
Growth Patterns of LGA Fetuses
Recent evidence shows that LGA fetuses demonstrate:
- Larger biometry measurements from as early as 20 weeks' gestation 5
- Consistently higher fetal adiposity measures throughout pregnancy 5
- Accelerated growth trajectories compared to appropriate-for-gestational-age (AGA) fetuses 5
Long-term Implications
LGA birth has significant long-term health implications:
- For the child: Increased risk of childhood obesity and development of type 2 diabetes later in life 3
- For the mother: Women with both GDM and LGA delivery have a significantly higher risk of developing metabolic syndrome later in life (54.4% vs. 43.6% in women with GDM but AGA delivery) 6
Clinical Pearls and Pitfalls
- Early detection is crucial: Evidence suggests that second-trimester identification of LGA fetuses may predict future GDM development and LGA status at birth 4
- Differential diagnosis: Distinguish between constitutionally large fetuses and those with pathological overgrowth due to maternal diabetes or other conditions
- Avoid overdiagnosis: Using inappropriate growth charts for specific populations may lead to misclassification
- Prevention focus: Pre-pregnancy weight optimization represents the most effective modifiable intervention to reduce LGA risk 2
LGA identification and management requires careful consideration of both maternal and fetal risks to optimize outcomes for both mother and baby.