This is surprising, and controversial
There is no new evidence to show foetuses feel pain in the womb before 24 weeks, and so no reason to challenge the abortion limit, doctors say.
The Royal College of Obstetricians and Gynaecologists' review said foetuses are "undeveloped and sedated".
Brain connections are not fully formed, and the environment of the womb creates a state of induced sleep, like unconsciousness, they add.
No pain for almost the first two trimesters? Really?
The study comes amid efforts by some MPs - including Prime Minister David Cameron - to lower the existing abortion limit.
Mr Cameron argued in April that the time-limit for abortions should be cut to "20 or 22 weeks".
But on the issue of pain perception, the report says: "Connections from the periphery to the cortex are not intact before 24 weeks of gestation.
"As most neuroscientists believe the cortex is necessary for pain perception, it can be concluded the foetus cannot experience pain in any sense prior to this gestation."
It adds: "There is increasing evidence that the foetus never experiences a state of true wakefulness in utero and is kept, by the presence of its chemical environment, in a continuous sleep-like unconsciousness or sedation."