A LONGITUDINAL-STUDY OF UMBILICAL ARTERY DOPPLER WAVE-FORMS IN NORMAL-PREGNANCY - ANALYSIS USING LAPLACE TRANSFORM TECHNIQUES

Objective To analyse umbilical artery Doppler waveforms using the Lapl ace transform analysis technique, an alternative method of waveform sh ape analysis, and to determine the normal ranges for the variables of this technique throughout normal pregnancy. Design A prospective longi tudinal study. Setting Department of Obstetrics and Gynaecology, Notti ngham University Hospital. Sample A cohort of 17 healthy women investi gated every four weeks from the end of the first trimester until term. Methods Umbilical artery Doppler signals were recorded and analysed u sing the Laplace transform analysis technique. The median and interqua rtile ranges for each variable were determined and serial changes duri ng pregnancy described. Results Vessel wall tone decreases in the umbi lical artery at the beginning of the second trimester. Alpha, the vari able related to upstream flow conditions, also decreases at this stage of pregnancy but values are then comparatively stable from 24 weeks o f gestation until term. A fall in downstream resistance within the fet oplacental circulation during pregnancy is detected using the C-coeffi cient. Real pole appears to be of no value In the assessment of downst ream resistance to flow in the fetus. Conclusions The normal ranges fo r the Laplace transform analysis variables have been established for t he umbilical artery longitudinally through normal pregnancy. Changes i n fetal blood flow during complicated pregnancy can now be investigate d using this technique.