Placental glycogen

The quantity and distribution of glycogen has been studied in 86 placentae from the last trimester of pregnancy and 8 of 8 to 16 weeks gestational age. In the first trimester glycogen concentrations were high, between 4-5 to 6-5 mg/g of blood-free tissue, but from about 12 weeks to term the concentrations were within a narrow range around 1-5 mg/g. The level did not deviate appreciably from normal in a range of clinical conditions: diabetes, intrauterine growth retardation, pre-eclampsia or acute fetal distress, and was unaffected by the length of labour and whether or not the mother had been given an infusion of dextrose. Nor was it affected by a wide range of glucose concentrations in the maternal and fetal plasma and in the placental tissue itself or by insulin concentrations in either circulation. After the first few weeks of pregnancy glycogen in the placenta was shown to be restricted to the vicinity of major fetal blood vessels. Here it may be presumed to act as an energy reserve for vasomotor activity. All the evidence suggests that any importance placental glycogen may have is likely to be local, in relation to the placental vessels; a more general role, as an emergency energy source for the fetus, seems unlikely.