Placental Lakes

Placental lakes are irregular, echo poor spaces within the placenta, caused by pooling of maternal blood in the intervillous space, with slow swirling flow on Doppler. They matter because a few are normal, but many or large lakes are linked with raised maternal serum alpha fetoprotein, growth restriction and, in women with a uterine scar, placenta accreta spectrum.

• Large lakes measure 2 cm or more, and many lakes raise concern.
• Risk factors: advanced maternal age, previous caesarean section, multiparity, placenta previa.
• Isolated small lakes need no action.

Women have no symptoms. Some with large lakes have light bleeding or a small for dates uterus.

• Found at the anomaly scan.
• Normal examination in most.
• Differential diagnosis: normal venous lakes, placental infarct, intervillous haematoma, placental cyst, chorioangioma, accreta lacunae.
• Complications: fetal growth restriction, preeclampsia, placenta accreta spectrum with previous caesarean section, antepartum bleeding, preterm birth.

The approach is ultrasound with Doppler and a check for accreta features in women with a uterine scar.

• Ultrasound: anechoic or hypoechoic lacunae within the placenta with swirling slow flow (low velocity) on spectral Doppler.
• Count and size of lakes; look for loss of the retroplacental clear zone and bladder wall irregularity in women with a previous caesarean section.
• Uterine artery Doppler at 20 to 24 weeks; growth scans from 28 weeks; maternal serum alpha fetoprotein if measured.
• MRI where available when accreta is suspected.

The principle is surveillance of growth, with a plan for accreta spectrum when features are found.

• Supportive: reassure for small isolated lakes; avoid smoking; daily fetal movement counts; teach to attend for bleeding.
• Pharmacological: aspirin 150 mg oral at night from 12 weeks to 36 weeks if uterine artery Doppler is abnormal or preeclampsia risk is high; ferrous sulphate 200 mg oral 8-hourly for anaemia; betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days if preterm delivery is likely; oxytocin 10 IU IM at birth.
• Procedures: growth scans every 4 weeks from 28 weeks; delivery at 39 to 40 weeks for isolated lakes; for suspected accreta spectrum plan caesarean birth at 34 to 36 weeks in a tertiary unit with 4 to 6 units of blood and surgical and anaesthetic teams.
• Special groups: women with a previous caesarean section and large lakes with a low placenta need review for accreta spectrum and delivery in a tertiary unit.
• Red flags: antepartum bleeding, falling growth centile, hypertension, abnormal Doppler, reduced fetal movements.
• Follow-up: repeat scan at 28 and 32 weeks; antenatal review every 2 to 4 weeks; placental histology after birth.