Functional magnetic resonance imaging (magnetization transfer) and stereological analysis of human placentae in normal pregnancy and in pre-eclampsia and intrauterine growth restriction.

Magnetic resonance imaging provides a non-invasive method for investigating functional changes in the human placenta in vivo. In this study, we combine a magnetic resonance imaging technique called magnetization transfer with established stereological methods in order to analyse and compare placentae from normal (16-36 weeks of gestation) and complicated (pre-eclampsia, intrauterine growth restriction) pregnancies. Magnetization transfer provided an in vivo measure of the ratio of bound protons:total protons and stereological analysis of histological sections was used to estimate a residual:total volume ratio (the ratio of non-vascular volume to total placental volume). Statistical comparisons were drawn using tests for related samples (longitudinal data) or one-way analysis of variance (cross-sectional data). We found no significant differences in magnetization transfer between gestational age groups or between uncomplicated pregnancies and pregnancies complicated by pre-eclampsia or intrauterine growth restriction. In comparable groups of different subjects, stereological analyses also failed to demonstrate significant differences in residual:total volume ratios. We conclude that [a] the ratio of non-vascular volume:total placental volume does not alter between 16 and 36 weeks of normal gestation, and [b] this integrated response is also conserved in pre-eclampsia and intrauterine growth restriction.