Revision as of 10:43, 16 November 2009

601

Demographic studies of fertility ¹ deal with certain phenomena connected with human childbearing ² or reproduction ². The term natality ¹ is sometimes used instead of fertility. These terms refer to the frequency of occurrence of births ³ or more specifically live births ⁴ — within populations and sub-populations. A birth is the process of delivering a child. Live births or the births of live-born children ⁵ are distinguished from late foetal deaths (cf. 411-5) by evidence of life, such as respiration, movement of voluntary muscles or heartbeat of the child after complete expulsion or extraction. The term effective fertility ⁶, which was once used to indicate that late foetal deaths were not counted among the total number of births, should refer to the cases in which the deaths of infants or children are excluded from consideration. The term differential fertility ⁸ designates fertility differences between the subgroups of a population.

• 1. On the meaning of the term fertility in demography, see also § 623.
• 2. Reproduction, n. - reproduce, v. - reproductive, adj. Frequently, reproduction refers to the balance of births and deaths (as in § 711) rather than to the process of childbearing or procreation.
• 3. The word birth is now commonly used to mean live birth.
• 4. Live-born, adj. also used as noun to mean: infant born alive.

602

Conception ¹ results from the fertilization ² of an ovum ³ by a spermatozoon ⁴ or sperm cell ⁴ and marks the beginning of pregnancy ⁵ or gestation ⁵ for the impregnated woman. In the course of its development the product of conception ⁶ is successively called an embryo ⁷ and then a foetus ⁷ — sometimes written as fetus ⁷. The moment at which the embryo becomes a foetus is not precisely determined: certain scientists set it at the end of 12 weeks or three months of intra—uterine life, although successive developmental stages after the eighth week are often termed foetal. Nidation ⁸ refers to the implantation of the egg in the wall of the uterus ⁹ or womb ⁹, a process which occurs a few days after fertilization.

• 1. Conception, n.- conceive, v.
• 2. Fertilization, n. - fertilize, v.
  Artificial fertilization: fertilization obtained by artificial insemination, i.e. by a process other than coitus (627-2).
• 3. A fertilized ovum is called an egg or zygote.
• 5. Pregnancy, n. - pregnant, adj.: gravid, expectant. Certain scientists consider that a pregnancy begins only at the time of nidation (602-8) of the egg.
• 7. Embryo, n. - embryonic, adj. - embryology, n.: the science dealing with the development of the embryo.
  Foetus or fetus, n. - foetal or fetal, adj. (cf. 411-).
• 9. Uterus, n. - uterine, adj.

603

A foetus is said to be non-viable ² during the first part of a pregnancy and viable ¹ thereafter. The change occurs when the foetus becomes capable of independent existence outside its mother, which is commonly considered to take place when the period of gestation ³ or duration of pregnancy ³ has exceeded 28 weeks. If the pregnancy has lasted longer than this, the expulsion of the foetus (alive or dead) takes place during confinement ⁴; an earlier explusion associated with an early foetal death is called an abortion ⁵ (cf. § 604). The period of about six weeks after delivery (during which the uterus usually regains its normal size and in which the probability of conception is low) is called the puerperium ⁶.

• 1. Viable, adj. - viability, n.
• 2. The minimum period determining viability varies between 20 and 28 weeks among countries, but the World Health Organization has recommended that 28 weeks be the standard time period. Generally the duration of pregnancy is computed from the onset of the last menses. This constitutes the conventional duration of pregnancy, as opposed to the true duration of pregnancy, computed from the time of conception.
• 4. The actual process of expulsion of the foetus is called delivery or parturition, which is the termination of labor. In addition to those, confinement includes expulsion or removal of the placenta or afterbirth.
• 5. Abortion, n. - abort, v.t. or v.i. - abortifacient, adj. used as n.: capable of inducing abortion. - abortionist, n.: a person who performs abortions. In everyday language, the term abortion often takes the meaning of induced abortion (604-2), as opposed to spontaneous abortion (604-1).
• 6. Puerperium, n. - puerperal, adj. (cf. 424-4).

604

Abortions following a non-induced infra-uterine death, which may have occurred some time before expulsion, are called spontaneous abortions ¹ or miscarriages ¹, in contrast to intentional abortions ², or induced abortions ². A therapeutic abortion ³ is one undertaken for medical reasons. The laws of certain countries permit abortions for health or other reasons; these are legal abortions ⁴. Abortions which are induced contrary to law are called illegal abortions ⁵ or criminal abortions ⁵. According to the technique used, there are abortions by curettage ⁶, abortions by vacuum aspiration ⁷, abortions by dilatation and evacuation ⁷, hysterotomies ⁸ (involving surgical cutting into the uterus), and abortions by medical induction procedures ⁹.

• 6. Also called abortions by dilatation and curettage, (abbreviated to D and C).
• 7. Also called abortions by suction. When the procedure is used very soon after a presumed conception, the terms menstrual regulation or menstrual extraction are used.
• 9. Such procedures involve amniotic fluid exchange as in the instance of an abortion by saline injection, or the use of prostaglandins.

605

Full term deliveries ¹ occur when the pregnancy has lasted at least 37 weeks, measured in conventional duration of pregnancy (603-3*). A pregnancy ending before the normal period is termed a premature delivery ² or premature confinement ² or premature birth ² and the product of this delivery is called a premature baby ⁴. Births which are not premature are called births at term ³ or full-term births ³ The word prematurity ⁵ is used to refer to phenomena connected with premature delivery. A classification of births by stage of development that does not depend upon an estimate of the period of gestation is used in many countries. In this classification a live-born infant with a birth weight ⁶ of 2,500 grams (5 1/2 lbs.) or less is said to be immature ⁸. Immaturity ⁷ is often combined with debility ⁹, an abnormal state of weakness.

606

At most confinements there is a single birth ¹ or single delivery ¹ but at some there are plural births ², multiple births ² or multiple deliveries ². Two children born during the same confinement are called twins ³ and we may distinguish between monozygotic twins ⁴, uniovular twins ⁴ or identical twins ⁴ on the one hand, and dizygotic twins ⁵ or biovular twins ⁵ on the other. Monozygotic multiple births occur when one ovum splits after fertilization; the resulting children must always be of the same sex. Dizygotic multiple births are .due to the simultaneous fertilization of two or more ova and the resulting children may be of different sexes.

• 2. In British official terminology the term maternity is used to denote a confinement resulting in the birth of one or more children; the number of births per maternity may be computed.
• 3. Where a multiple birth results in three children, these are-called triplets, four are quadruplets, and five quintuplets. The terms "twins", "triplets", etc. are generally used in accordance with the total number of deliveries during a confinement; occasionally, however, multiple births are classified only in accordance with the number of children born alive.