Sonographic detection of physiologic pleural fluid in normal pregnant women

Purpose This prospective study was conducted to determine the normal incidence of a small amount of pleural fluid in healthy pregnant women on sonography. Methods Chest sonography to detect pleural fluid was performed in 47 pregnant volunteers, first with the subjects leaning on 1 elbow (the “elbow position”) and then with subjects in a sitting position. A 9–12‐MHz linear‐array probe was used. If the result of this first examination was positive (showing a 2‐mm or thicker anechoic layer), the subject was rescanned with a 3–6‐MHz large‐radius curved‐array probe. Results A thin layer of fluid with a typical wedge‐shaped appearance was visible in the pleural cul de sac space of 28/47 (59.5%) pregnant volunteers, on both sides in 18/47 (38.3%) and unilaterally in 10/47 (21.2%). The mean (± standard deviation) thickness of fluid layer (mean of measurements obtained in both positions) was 2.9 ± 1.1 mm (range, 1.8–6.4 mm). The number of pregnant women with visible pleural fluid was the same regardless of the fetus' sex, but the difference in fluid layer thickness between the 2 groups was statistically significant (by the t‐test, p < 0.05). A fluid layer thicker than 3 mm was easily detected with the 3–6‐MHz abdominal curved‐array probe in 7/47 (15%) women. Conclusions Small amounts of pleural fluid can be visualized by chest sonography in healthy pregnant women. This result, if isolated, should not be taken as a sign of occult thoracic disease. © 2005 Wiley Periodicals, Inc. J Clin Ultrasound 33:63–66, 2005