Objective: To assess the elaboration of placental stem villous vessels from pregnancies complicated by intrauterine growth restriction (IUGR) with absent end-diastolic flow velocity detected prior to delivery in the umbilical artery.
Design: Comparison between IUGR and control groups of the distribution, in 15 microns increments of 600 randomly chosen stem vessel profiles (post-fixation diameter 10-160 microns) identified by immunohistochemical localisation of alpha-smooth muscle actin in the vessel media.
Setting: Clinical teaching hospital and university anatomy department.
Subjects: Paraffin-fixed blocks obtained from placentas of eight pregnancies complicated by IUGR and eight gestational age-matched controls.
Results: The distribution of the stem villous vessels in the IUGR placentas, as assessed by the mean vessel diameter in each case, did not differ from the controls (mean vessel diameter 31.8 microns [SD 2.4] vs 29.6 microns [2.3]; P = 0.13). In five IUGR cases alpha-smooth muscle actin positive cells (myofibroblasts) were identified within the stroma of nonmuscularised peripheral (mature intermediate and terminal) villi, but in none of the controls.
Conclusions: Our data do not support the theory that IUGR with absent end-diastolic flow velocity in the umbilical artery is due to a selective loss of small stem villous vessels. The increased impedance in this condition may be conferred more distally within the nonmuscularised capillaries of the peripheral villi.