Huxley's Brave New World was published in 1932. In it, they described depriving fetuses of oxygen in utero to create workers for menial tasks. At the time of course it was not technically or socially feasible, but nonetheless, they started trying immediately. By the late 1940's doctors had been trained to clamp the umbilical cord immediately after delivery, "immediate/early cord clamping", instead of allowing the proper completion of placental transfusion. This causes hypoxic brain damage in the infant, developmental stunting, and various other effects.

The claim about preventing neonatal jaundice is an excuse. The primary citation I've found is a study that found an incidence of 2% vs 5%, other confounders were poorly reported and not take into consideration, a recent cochrane review also found no real substantiation. Incidence was never high and never has been, the type of vitamin K they used at the time they were trying to bring this in occasionally caused jaundice, many things cause neonatal jaundice, and ultimately it's trivially treatable with photothereapy. I was reading the proceedings of a symposium from the late 50's where they were discussing phototherapy.

Failure to allow placental transfusion to complete in its own natural course causes measureable brain damage (lower myelination at 4 months, feritin remains low for 2-4 months), IQ reduction, and developmental stunting. Also due to the reduced ferritin levels it probably potentiates fenton reaction H2O2-> 2 OH, which is catalyzed further by exposure to ELF fields and myriad other environmental and endogenous stressors. Peroxynitrite and hydroxyl radical in particular will cause a lot of damage, and feritin is required to sequester free iron (which causes the fenton reaction). Feritin is important for other aspects of development in the perinatal period especially, as well.