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Demographic studies of fertility1 (621-3) deal with certain phenomena connected with human reproduction2. The term natality1 is sometimes used instead of fertility. These studies are mainly concerned with births3 and the birth rate (630-1) of populations and with the factors affecting them. A birth is the act or process of delivering a child. A distinction used to be made between a live birth4 resulting in the delivery (603-4*) of a live-born child5 and a stillbirth (410-6), the delivery after about the sixth month of pregnancy of a foetus that died before or during delivery. The term effective fertility6 has sometimes been used when late foetal deaths (410-6), and in some cases the deaths of infants or children, are excluded from consideration. The term total fertility7 has on occasions been used to refer to live births and late foetal deaths combined.
- 1. fertility n. — fertile adj.
- 2. reproduction n. — reproduce v. — reproductive adj.
- 3. It is becoming more and more common, to use the term birth to mean live births in view of the introduction of the term late foetal death for still births (410-6*).
Conception1, the fertilization2 of the female ovum3 by a male sperm4 or spermatozoon4 is the beginning of pregnancy5 or gestation5, which consists of the development of the product of conception6 in. the form of an embryo7 or foetus7 (the American spelling is fetus7). Although the distinction between an embryo and a foetus is not precisely defined, the term "embryo" is generally used for the earliest stages of foetal development. An early process in pregnancy is nidation8, the implantation of the fertilized ovum in the wall of the uterus9 or womb9.
- 1. conception n. — conceive v.
- 2. fertilization n. — fertilize v. 5. pregnancy n. — pregnant adj.
- 7. embryo n. — embryonic adj. — embryology n., the science dealing with the development of embryos. foetus n. — foetal adj. 9. uterus n. — uterine adj.
A foetus is said to be non-viable2 during the first part of a pregnancy and viable1 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 gestation3 or duration of pregnancy3 has lasted between 20 and 28 weeks. If the pregnancy has lasted longer than this, the expulsion of the foetus (alive or dead) takes place during confinement4; an earlier expulsion is called an abortion5 (cf. para. 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 puerperium6 (424-3).
- 1. viable adj. — viability n.
- 4. The actual process of the expulsion of the foetus is called delivery or parturition, which is the termination of labour.
- 5. abortion n. — abort v.
- 6. puerperium n. — puerperal adj.
A spontaneous abortion1, an unintentional abortion1 or, in nonmedical terms a miscarriage1 is an abortion which is not purposely caused. An intentional abortion2 or induced abortion2 is one which is purposely caused. A therapeutic abortion3 is one which is undertaken to safeguard the health of the mother. The laws of certain countries permit legal abortions4 for health or other reasons. Abortions which are induced contrary to law are called illegal abortions5 or criminal abortions5.
- 1. miscarriage n. — miscarry v.
Confinements (603-4) and deliveries (603-4*) are said to occur at term1 when the pregnancy has lasted for the normal period of about nine months. If pregnancy ends before the normal period (but after six months) there is a premature delivery2 or premature confinement2 or premature birth2 and the product of conception is called a premature baby4. Births which are not premature are called births at term3 or full-term births3. The word prematurity5 is sometimes 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 weight6 of 5,5 lb. (2,500 grammes) or less is said to be immature7.
Almost confinements there is a single birth1 or single delivery1, but at some there are plural births2, multiple births2 or multiple deliveries2. Two children born during the same confinement are called twins3 and we may distinguish between monozygotic twins4, uniovular twins4 or identical twins4 on one hand, and dizygotic twins5, biovular twins5, fraternal twins5 or non-identical twins5 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.
- 1. Single births result in one child only, who in medical literature is sometimes called a singleton.
- 2. The number of infants born in each delivery has been called litter size by some biometricians but in general, this term is reserved tor animals.
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 called quadruplets and five quintuplets. The terms "twins", "triplets", etc. may be used in different ways. Generally they are used in accordance with the total number of deliveries during a confinement, especially if at least one baby is born alive, e. g. one of a pair of twins may be alive when delivery is complete and the other dead. Occasionally, however, multiple births are classified only in accordance with the number of children born alive.
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