There are studies that find a correlation, but not causation.
"Birth injury causes nursing strikes". The cause of this myth is likely derived from hospital policies. Which require breastfeeding mothers to refrain from breastfeeding for 24 hours after having had an epidural anesthesia. This causes some mothers to believe that their babies are refusing to breastfeed because it is "injured."
In most cases, there is no way to know if what caused your child's refusal to nurse was an injury sustained during childbirth or not. What usually happens with babies who do experience negative reactions. After having difficulties at birth, is that they may refuse or suddenly stop feeding altogether. Because they are exhausted and overstimulated by the whole experience which makes them too sensitive for it all.