Introduction The presence of reduced fetal movements (RFM) is associated with increased incidence of fetal growth restriction (FGR) and stillbirth. RFM is thought to represent fetal compensation to nutrient and oxygen deprivation resulting from placental insufficiency. Evidence of this has been identified in FGR, but no such investigations have been undertaken in RFM. We aimed to assess whether placentas from RFM-affected pregnancies have altered placental structure and function.

Methods Placentas were collected from women with RFM if they delivered within 1 week of presentation (n=36) and analysed for macroscopic changes using photographs and weights, microscopic changes through histological and immunohistochemical studies and functional changes through System A amino acid transporter activity (n=12). Women with normal FM were used as controls (n=18).

Results Significant structural and functional differences exist between RFM and normal placentas. RFM placentas were smaller, with reduced weight (471.2 g vs normal 539.5 g; p<0.05), reduced surface area (220.4 cm² vs normal 262.1 cm²; p<0.005) and more infarcts (3.5% vs normal 0.6%; p<0.01). Microscopically, the placental villi displayed reduced vascularity (5.6 vs normal 6.6 capillaries/terminal villus; p<0.001), reduced syncytiotrophoblast area (19.8% vs normal 14.8% of total villous area; p<0.01) and increased syncytial knots (89.9 vs normal 25.0 knots/mm²; p<0.001) compared to normal. These structural abnormalities were associated with reduced System A activity (60.6 vs normal 94.2 pmol/mg protein).

Discussion In women who deliver within 1 week from presentation RFM is associated with altered placental structure and function, suggesting that women with RFM merit further antenatal investigation to identify those with placental insufficiency.