Embryonic and fetal tiny pericardial fluid collections at less than 12 weeks of gestation.

Objectives: To describe embryonic and fetal tiny pericardial fluid collections (PFCs) using transvaginal sonography and HDlive Silhouette at less than 12 weeks of gestation.

Methods: During an 8-month period from November 2021 to June 2022, one-hundred and thirty transvaginal scans were performed for first-trimester dating, and eleven tiny PFCs of the embryo or fetus were identified at 8+4 - 11+3 weeks of gestation (three at 8, six at 9, and two at 11 weeks). HDlive Silhouette features of PFC were evaluated. Their clinical characteristics and outcomes were also investigated.

Results: The incidence of tiny PFCs was 8.5 % at less than 12 weeks of gestation. The mean gestational age at the initial examination was 9.5 weeks (SD: ± 0.9). The mean crown-rump length was 25.0 mm (SD: ± 8.5). The mean PFC dimension was 0.8 mm (range: 0.5-1.3, SD: ± 0.2). Pleural effusion was associated with 3 out of 11 PFCs (27.2 %). Ascites was noted in 2 cases (18.2 %). Skin edema was identified in only in 1 case (0.09 %). There was no arrhythmia. Tiny PFC could also be depicted using HDlive Silhouette. First-trimester fetal ultrasound scans at 11 - 13+6 weeks showed no abnormal findings. PFCs resolved until 13 weeks of gestation (Mean: 12 weeks, SD: ± 1.2). All PFC pregnancies resulted in healthy neonates.

Conclusions: The incidence of tiny PFCs was relatively high in early pregnancy. HDlive Silhouette can depict tiny PFCs of the embryo. Tiny PFCs in early gestation are transient, benign findings in utero.