"Hemodynamic and neuroendocrine changes in fetuses undergoing stressful procedures have also been used to infer pain perception. As early as 16 weeks’ gestational age, fetal cerebral blood flow increases during venipuncture and transfusions that access the fetal hepatic vein through the innervated fetal abdominal wall but not during venipuncture and transfusions involving the noninnervated umbilical cord. Increased cerebral blood flow is not necessarily indicative of pain, as this response is thought to constitute a “brain sparing” mechanism associated with hypoxia and intrauterine growth restriction."