Johnson, Pamela Valerie; (1993) Cardiovascular pressures in the human fetus. Doctoral thesis (M.D), UCL (University College London).

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Abstract

The technique of ultrasound guided fetal blood sampling has been adapted, as herein described, to permit measurement of intra amniotic, intra umbilical vascular and intra cardiac pressures in the human fetus in utero during indicated procedures. 246 pregnancies have been investigated and reference ranges for these pressures established. The effects of fetal disease on these pressures has been examined. Intra amniotic pressure in the presence of a normal liquor volume is unaffected by fetal abnormality, and increases with gestation. Measurement of intra amniotic pressure in abnormal liquor volumes provides widely varying results and has no proven clinical value. Umbilical venous pressure does not increase with gestation and is not affected by fetal abnormality unless this involves the fetal heart. In nonimmune hydrops, there is a significant relationship between umbilical venous pressure and cardiac size, providing for the first time direct evidence of intrauterine cardiac failure in some cases of hydrops. Elevation of venous pressure also occurs in congenital heart disease if cardiomegaly is present, and congenital diaphragmatic hernia with associated left ventricular compression. Umbilical arterial pressure increases with gestation, and is elevated in the presence of abnormal umbilical artery Doppler blood flow studies and fetal hypoxia. Left and right atrial pressures do not increase with gestation. Although the pressure in the right atrium is higher than the left, this is not statistically significant. Elevation of atrial pressure occurs in nonimmune hydrops with associated cardiomegaly. Left and right ventricular pressures are equal and both systolic and end diastolic pressures increase with gestation. The pressure waveforms are similar to those obtained in postnatal investigations. Abnormalities of pressure waveforms and actual values occur in cases of left and right ventricular outflow obstruction, and these measurements provide additional diagnostic and prognostic information. This study provides new data on umbilical venous pressure in the presence of fetal abnormality and intrauterine cardiac failure. It also provides the results of the first direct measurements of human fetal cardiac pressures in normal and abnormal hearts.

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