Squamous cells in the maternal pulmonary circulation.

Identification of squamous cells in the maternal pulmonary arterial circulation, either at autopsy or in blood aspirated from a pulmonary artery catheter, is currently regarded as pathognomonic for amniotic fluid embolism. Sixteen pregnant women underwent pulmonary arterial catheterization for a variety of medical indications. Examination of the buffy coat fraction of the distal lumen aspirate resulted in the identification of squamous cells in all cases. Squamous cells were similarly identified in control specimens from 17 nonpregnant patients; however, the difference in cell count between the pregnant and nonpregnant patients was significant. Such cells presumably reflect, in part, bloodstream contamination from sites of venous access. Reliable differentiation of adult from fetal squamous cells is not possible; however, the significant increase in cell count documented in pregnant patients suggests a possible fetal origin for some squamous cells detected during pregnancy. The detection of squamous cells in the pulmonary arterial circulation of pregnant women is not pathognomonic for amniotic fluid embolism. In a critically ill obstetric patient, such a finding should not deter the clinician from a thorough search for other causes of hemodynamic instability.