The case of a mother who was discharged from St Michael's Hospital in Bristol six hours after giving birth was not unusual, it said. Pain-killing epidural drugs were being refused on request, and given only in emergencies.
Anne Jackson-Baker, the director, said: "St Michael's is unusual because they are being upfront about it. But it is happening at many hospitals throughout the country, because of staff shortages.
"If a mother wants to go home after a short time, she should. But many are going home to shared accommodation, and awful bathroom facilities, and it could be too soon.
"What is worse is that nervous mothers, who fear they will not be able to cope with the pain of childbirth, are not being given the option of having an epidural. That is because one-to-one care is needed and, because there are too few midwives, they cannot have it."
The United Bristol Healthcare NHS Trust sent a letter to expectant mothers, explaining that lack of staff meant epidurals could not be administered on request, and that if a mother felt able, she could be discharged within six hours of giving birth.
The Royal College of Midwives said staff shortages were particularly bad in the South and South-west.
There are 32,803 midwives in the UK, 2,500 fewer than two years ago, according to the United Kingdom Central Council register. The shortage is more acute because more midwives are working part time.
The Department of Health said it understood that mothers were not forced to go home, but did so only if they felt able. A spokesman said: "If it is considered clinically safe and the mother wants to go home, then we agree. But the mother has to be happy with the situation."
Alan Duncan, Conservative health spokesman, said: "Labour has already proved a let-down for our health service. Now they are letting down new mothers as well."