Management of Placenta Lakes
Primary Recommendation
Placenta lakes are generally benign findings that do not require specific intervention, but large placental lakes (>2 cm × 2 cm) identified in the second trimester warrant increased fetal surveillance for the remainder of pregnancy due to association with small-for-gestational-age status. 1
Understanding Placenta Lakes
Placental lakes are sonolucent or hypoechoic areas within the placenta, typically representing physiological dilation of the intervillous space. 2, 3 They occur in approximately 2.2% of pregnancies and are usually considered a normal variant. 3
Clinical Significance Based on Size
Small Placental Lakes
- Small placental lakes (<2 cm × 2 cm) are not associated with adverse pregnancy outcomes. 3
- No statistically significant differences in birth weight, gestational age at delivery, or adverse obstetric outcomes have been demonstrated. 3
- Routine obstetric care is appropriate without additional surveillance. 3
Large Placental Lakes
- Large placental lakes (≥2 cm × 2 cm) are significantly correlated with fetal small-for-gestational-age status. 1
- These require appropriate surveillance for the remainder of pregnancy. 1
- Some large placental lakes may decrease or disappear during pregnancy, while others persist. 1
Recommended Management Approach
Initial Assessment
- Document the size of placental lakes when identified during second-trimester anatomy scan (20-22 weeks). 1, 4
- Measure dimensions to determine if lakes are ≥2 cm × 2 cm in diameter. 1
- Perform color Doppler examination to characterize blood flow patterns and exclude other pathologies. 2, 5
Surveillance Protocol for Large Placental Lakes
- Serial ultrasound examinations for fetal growth assessment at 2-4 week intervals in the third trimester. 6
- Monitor for development of fetal growth restriction using umbilical artery Doppler studies. 6
- Reassess placental lake size at 30-32 weeks gestation to determine if persistence or resolution has occurred. 1, 4
Differential Diagnosis Considerations
Important caveat: Not all anechoic placental areas are benign placental lakes. The differential diagnosis includes: 5
- Placenta accreta spectrum disorder (particularly with multiple lacunae)
- Placental tumors (chorioangioma)
- Subchorionic hematoma
- Placental infarction
If multiple lacunae are present or there are concerning Doppler findings, evaluate for placenta accreta spectrum disorder, especially in patients with prior cesarean delivery or placenta previa. 6, 7
Delivery Planning
Timing of Delivery
- Routine timing of delivery is appropriate for isolated placental lakes without fetal growth restriction. 3
- If fetal growth restriction develops, follow standard protocols for timing of delivery based on Doppler findings and gestational age. 6
Mode of Delivery
- Mode of delivery is not affected by the presence of placental lakes alone. 3
- Standard obstetric indications should guide delivery decisions. 3
Key Clinical Pitfalls to Avoid
- Do not dismiss large placental lakes (≥2 cm) as entirely benign—they require fetal growth surveillance. 1
- Do not confuse placental lakes with placental lacunae of placenta accreta spectrum, which have different Doppler characteristics and clinical implications. 6, 5
- Do not perform digital cervical examination until placenta previa has been excluded if placental abnormalities are identified on ultrasound. 7
- Do not assume all placental lakes will persist—some decrease or resolve during pregnancy, necessitating follow-up imaging. 1
Pathologic Examination
Histopathologic examination of the placenta after delivery is reasonable when large placental lakes were identified prenatally, to understand underlying pathophysiology and guide counseling for future pregnancies. 6