Women who have previously given birth have more relaxed uterine muscles which are more sensitive to fetal motion during subsequent pregnancies.
[4] Quickening indicates the start of fetal movements, usually felt 14–26 weeks after conception, or between the fourth and sixth month.
However, due to the greater impact of local customs and contested jurisdictions in earlier stages of legal history, the customary origins of the common law are murky, and scholars can point to other cases where abortion was not considered such a serious matter.
[11] Blackstone explained the subject of quickening in the eighteenth century, relative to feticide and abortion: Life... begins in contemplation of law as soon as an infant is able to stir in the mother's womb.
The law held that no women could be granted a second reprieve from the original sentence on the ground of subsequent pregnancy, even if the fetus had quickened.