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 mis-attributed 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 primigravida woman) typically feels fetal movements at about 18–20 weeks, whereas a woman who has been pregnant more than once (i.e., a multipara woman) will typically feel movements around 15–17 weeks.
The word "quick" originally meant "alive". 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 de 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 fetus 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 before Bracton. For example, in the Septuagint text of the Old Testament, killing the fetus was considered to be taking a life, "if it be perfectly formed". However, other translations of exactly the same verses maintain that killing the fetus was considered to be taking a life without regard to its physical formation. Thus, quickening perceived by a woman has been only one of the standards used to mark when a human life legally begins. Others include viability, birth, and conception.
In the eighteenth and nineteenth centuries, a woman convicted of a capital crime could claim a delay in her execution if she were pregnant; a woman who did so was said to "plead the belly". In Ireland on 16 March 1831 Baron Pennefather in Limerick stated that pregnancy was not alone sufficient for a delay but there had to be quickening.
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- Blackstone, William (1979) . "Amendment IX, Document 1". Commentaries on the Laws of England 5. Chicago: University of Chicago Press. p. 388.
- Henry de Bracton (1968) [c. 1250]. "The crime of homicide and the divisions into which it falls". In George E. Woodbine ed.; Samuel Edmund Thorne trans. On the Laws and Customs of England 2. p. 341. OCLC 1872.
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- "Exodus", Septuagint LXX in English, translated by Lancelot Brenton. (Bagster & Sons 1851). The Septuagint text was written in 285-246 BC.
- Keil, F. & Delitzsch, F., Biblical commentary on the Old Testament, Volume II, pages 134-135 (T. & T. Clark 1869)
- Limerick Evening Post and Clare Sentinel, 18 March 1831.
- First Fetal Movement : Quickening, American Pregnancy Association.
- Fetal movement: Feeling your baby kick, babycenter.com.