There is no new evidence to show fetuses feel pain in the womb before 24 week, UK doctors say.
The Royal College of Obstetricians and Gynaecologists' review said fetuses 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.
Anti-abortion campaigners challenged the reports.
The issue of whether a fetus of 24 weeks or below can feel pain had been raised in the debate over whether the current time limit for abortion should be reduced.
The first of the college's reviews examined whether or not a fetus can experience pain.
It found that nerve connections in the cortex, the area which processes responses to pain in the brain, does not form properly before 24 weeks.
The report states: "It can be concluded that the fetus cannot experience pain in any sense prior to this gestation."
Even after 24 weeks, the college concluded a fetus is naturally sedated and unconscious in the womb.
This could mean that late abortions, which are permitted for serious abnormalities or risks to the mother's health, may not result in fetal suffering.
In addition, the report says anaesthetics, which can be risky, would not be required if a fetus requires surgery.
It also tried to define what mental and physical abnormalities could result in a "serious handicap".
One per cent of abortions are carried out on these grounds. Such terminations can take place after 24 weeks.
Ann Furedi, chief executive of the British Pregnancy Advisory Service (BPAS), said taken together the two reports would provide a clear basis for difficult decisions.Source