According to one of the studies:
Sleep deprivation can cause changes in the levels of hormones involved in appetite regulation. Keep in mind, though, that there are multiple factors involved in causing postpartum women to sleep less. These include just having a newborn, having other small children at home, possible postpartum depression, illness of the newborns, if any, work, etcetera.
Most every mother would love to hit the hay for a bit longer, but making it happen isn't necessarily a matter of choice. What's your take on the issue?