Some 31 female prisoners gave birth while serving jail terms in the nine months to March 2021 in England and Wales, new figures show.
Data from the Ministry of Justice reveals that 29 women in custody gave birth in hospital, and two gave birth on the way to hospital.
In the year to March 2021, 19 babies were received into prison mother and baby units.
On average, there were 26 pregnant women in prison per week in the nine months to March 2021.
There have been renewed calls in recent days to stop jailing pregnant women after a report found there were "missed opportunities" to help a prisoner who gave birth to a stillborn baby in her cell toilet.
Mother Louise Powell, who did not know she was pregnant, said she “cannot forgive” the prison for what happened.
Prisons and probation ombudsman (PPO) Sue McAllister said staff made a “serious error of judgment” when they did not visit Powell or properly assess her after she started bleeding and reported being in pain – Read more: Fear of more baby deaths as ministers stand firm on jailing pregnant womenwrongfully deciding she was having a painful period.
The watchdog's report found Powell was forced to give birth in “shocking circumstances”.
The findings come just months after a damning report revealed how a newborn baby died after a teenage girl gave birth alone in a cell in Europe’s largest women’s prison, HMP Bronzfield in Middlesex, despite calling staff for help.
In this report, Ms McAllister said the mother suffered a “terrifying, painful and traumatic experience” and described the case as “deeply sad and distressing”.
Prison staff called the duty nurse three times to raise concerns about the prisoner over two hours but, without visiting her or properly assessing her, “concluded incorrectly that she was bleeding and suffering severe stomach pain as a result of a painful period”.
The report added: “Regardless of the cause, it is not acceptable that anyone should be in unexplained acute pain for several hours without proper assessment or consideration of pain relief.”
Kate Paradine, chief executive of Women in Prison, said: “This is the second time a tragedy like this has happened in nine months.
"How many times do we need to address this avoidable sadness and pain before the government ends the harm and violence inflicted by our prison system?
"Time and time again, we hear that women are not able to access vital healthcare with devastating consequences.
"While women continue to be imprisoned, tragedies like this will continue to happen.
"The government must act now, starting with the immediate release of women from prison.
"Only investment in community support will keep our communities safe from harm.”
Prisons minister Victoria Atkins said: “The tragic events detailed in this report should quite simply never happen to any woman or child, and my deepest sympathies remain with the mother.
“We have already implemented the report’s recommendations and important improvements have been made to the care received by pregnant women in custody. We are also looking at how we can better screen for pregnancy in jails so no woman falls through the cracks.
“But there is clearly much more to do to ensure expectant mothers in prison get the same support as those in the community – something I will continue to prioritise.”
Watch: Daily politics briefing, 18 January