Quickening

Overview
In pregnancy terms, the moment of quickening refers to the initial motion of the fetus in the uterus as it is perceived or felt by the pregnant woman. According to the Oxford English Dictionary, to "quicken" means "to reach the stage of pregnancy at which the child shows signs of life." In the twentieth century, ultrasound technology made it possible to see that a fetus is in motion even if the pregnant woman does not yet feel it. This technological development made the concept of "quickening" a bit more complex.

Medical facts
The first natural sensation of quickening may feel like a light tapping, or the fluttering of a butterfly. These sensations eventually become stronger and more regular as the pregnancy progresses. Sometimes, the first movements are misattributed to gas or hunger pangs.

A woman’s uterine muscles, rather than her abdominal muscles, are first to sense fetal motion. Therefore, a woman’s body weight usually does not have a substantial effect on when movements are initially perceived. Women who have already given birth have more relaxed uterine muscles that are consequently more sensitive to fetal motion, and for them fetal motion can sometimes be felt as early as 14 weeks.

Usually, quickening occurs naturally at about the middle of a pregnancy. A woman pregnant for the first time (i.e. a primiparous woman) typically feels fetal movements at about 20-21 weeks, whereas a woman who has already given birth at least two times (i.e. a multiparous woman) will typically feel movements around 18 weeks.

Legal history
Historically, quickening has sometimes been considered to be the beginning of the possession of "individual life" by the fetus. British legal scholar William 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. For if a woman is quick with child, and by a potion, or otherwise, killeth it in her womb; or if any one beat her, whereby the child dieth in her body, and she is delivered of a dead child; this, though not murder, was by the ancient law homicide or manslaughter. But at present it is not looked upon in quite so atrocious a light, though it remains a very heinous misdemeanor.

Nevertheless, quickening was only one of several standards that were used historically to determine when the right to life attaches to a fetus. According to the "ancient law" mentioned by Blackstone, another standard was formation of the fetus, which occurs weeks before quickening. Henry Bracton explained the ancient law, about five hundred years before Blackstone:

If one strikes a pregnant woman or gives her poison in order to procure an abortion, if the foetus is already formed or quickened, especially if it is quickened, he commits homicide.

The rule that a fetus was considered alive upon formation dates back at least another millennium. In the Septuagint text of the Old Testament, formation of the fetus was emphasized instead of quickening, according to the Book of Exodus:

22 And if two men strive and smite a woman with child, and her child be born imperfectly formed, he shall be forced to pay a penalty: as the woman’s husband may lay upon him, he shall pay with a valuation. 23 But if it be perfectly formed, he shall give life for life, 24 eye for eye, tooth for tooth, hand for hand, foot for foot, 25 burning for burning, wound for wound, stripe for stripe.

Thus, in the earliest history of Judeo-Christian tradition, the highest value for life was thought to accrue when the fetus is formed. Later in history, the moment of quickening became the predominant standard for a right to life. Ultimately, the moment of fetal viability became more significant, although the moment of conception has also been used as a standard for when the right to life legally attaches to a human being.