The postpartal thickness of the amniochorionic membrane was measured by means of 20 MHz ultrasound after 28 inconspicuous deliveries in the course of a prospective study. The aim of our investigation was to determine the thickness of the amniochorionic membrane using high frequency ultrasound and to evaluate the results for a statistical correlation with fetal and maternal parameters. The data obtained were compared with histological sections for measurement accuracy using a linear regression analysis method. Membrane thickness of the total study group was 0.83 +/- 0.11 mm (0.72-1.08 mm). Based on a statistical comparison with the histological sections, the high frequency ultrasonographic examination was shown to be highly reliable with a correlation coefficient of r = 0.96 (p < 0.0001). Results obtained by ultrasonography were correlated with maternal (gestational age, patient age, parity) and neonatal (size and weight at birth, sex, placental weight, Apgar 1/5/10) parameters by means of linear regression analysis. There was a statistically significant correlation between parity and membrane thickness (r = 0.485, p < 0.05). There was also a correlation of Apgar scores at 5 minutes post partum (r = 0.485, p < 0.05). We were able to demonstrate that the measurement of membrane thickness by ultrasound is an objective and reliable method and may be a gain to prenatal diagnostics when used in vivo.