As a species we have evolved to have very large brains compared to our body size, meaning that for us childbirth can be a relatively traumatic experience. Labour lasts much longer for us compared to other mammals, we often require assistance and without pain relief it can be a very painful process for the mother.
Babies cannot talk and therefore cannot tell us if they are experiencing pain so we have to look at other factors to determine if they are suffering pain or not. Until only a few decades ago scientists believed that babies were unable to sense pain. That view has now changed and it has been shown that babies have the same if not more pain receptors in the skin as adults.
Pain levels in babies can be measured by physiological parameters such as blood pressure, heart rate and levels of circulating stress hormones such as cortisol. Research based on these parameters suggests that babies experience significant pain during birth. Caesarean births seem to be the least painful mode of delivery for the baby and assisted vaginal births (such as vacuum extraction) the most painful.
Some evidence suggests that the pain experienced by the baby during birth can actually be beneficial. The high levels of stress hormones released in response to pain during birth help with the onset of breathing. This may explain why babies born by caesarean section are more likely to suffer breathing difficulties than those that had a vaginal birth.
At birth a baby’s brain is not fully developed and it is thought that, although babies experience significant pain during birth, because their brains (especially the regions involved in memory formation) are not fully developed they do not remember this traumatic experience.