To discuss prenatal ultrasonographic characteristics of placental lake-like lesions and the significance of prenatal diagnosis of these lesions.

Six patients with prenatal placental lake-like lesions (maximal diameter>5 cm) detected by ultrasound were selected from Beijing Obstetrics and Gynecology Hospital, Capital Medical University from February 2016 to December 2021. Their demographic data, ultrasound features, clinical diagnoses and pregnancy outcomes were retrospectively analyzed.

All the patients had a singleton pregnancy, aged 27-33 years at diagnosis, and were initially found with placental lake-like lesions at 18 weeks and two days of pregnancy to 31 weeks and 6 days of pregnancy. Lake-like lesions with clear margins with placenta were detected by ultrasound in cases 1, 2 and 3, all of them were clinically diagnosed with massive subchorionic hematoma (MSH) , then underwent ceserean section at less than 34 weeks but greater than 33 weeks of pregnancy, less than 30 weeks but greater than 29 weeks of pregnancy, and 32 weeks of pregnancy, respectively, and all of 3 neonates had hypospadias. In case 4, a lake-like lesion with definite border protruding into amniotic cavity was found, which spontaneously disappeared in minutes. Fetal growth was unremarkable during pregnancy. In follow-up, the lesion was decreased significantly. Final diagnosis was real large placental lake. In cases 5 and 6, lake-like lesions diffusely involved most part of placenta, with decreased normal placental tissues. Both cases were complicated by early-onset fetal growth restriction (all biometric parameters<1%, abdominal circumference 2.3%) . Absence of diastolic flow in umbilical artery and notches in uterine arteries (bilateral, unilateral) were found in ultrasound examinations in both cases. Case 5 chose to terminate pregnancy at 23 weeks of pregnancy, and case 6, who was also complicated by preeclampsia, terminated pregnancy at less than 28 weeks but greater than 27 weeks of pregnancy. Clinical diagnosis for both of them was maternal vascular malperfusion (MVM) with early-onset FGR.

Placental lake-like lesions can be caused by different etiologies. Each type can be differentiated according to ultrasound characteristics. Timely prenatal diagnosis by ultrasound will benefit close monitoring of fetal status in MSH and MVM cases to prevent negative pregnancy outcomes.