Length of Human Gestation With Special Reference to Prematurity

Abstract

Prematurity is regarded as an important predisposing cause of numerous pathological conditions in early infancy. It is the greatest single cause of early loss of infant life, deaths classified under this heading being 8861 out of a total of 14,002, or 63 yo, in the first year of life.The premature child is relatively unprotected against infection and has difficulty in obtaining adequate nutrition.The conditions associated with prematurity such as poor maternal health, multiple pregnancies, foetal deformity have been enumerated by investigators (Brown, Lyon & Anderson, 1945; Crosse, 1945, etc.), but the cause of prematurity in a large number of cases is unknown.That the normal dangers of birth trauma of the central nervous system are increased in cases of prematurity is the general opinion of medical authorities, and this is confirmed by observation. The results of an investigation by Nevinny (1936) show something of the extent of these particular dangers.Nevinny had access to data of 15,130 infants of 1500 g. (34 lb.) or over, among which were ninety-three deaths accompanied by birth trauma confirmed by autopsy. Of these, forty-eight were cases of spontaneous birth and forty-five were of delivery by operation. Table 1 shows the data divided into groups of spontaneous and operative delivery for premature and full-term foetuses. The number of deaths with birth trauma is given as a percentage of the cases confirmed by autopsy, showing 34 yo among the premature as compared with 25 yo among the full-term in the cases of spontaneous delivery. For operative delivery the proportion is about one-half of the deaths, whether for premature or full-term foetuses. It may be observed that the number of autopsies carried out was not, in any group, a large proportion of the deaths from all causes; perhaps it was a selected group, so that the proportions 34 and 25 yo, if applied to the numbers 128 and 190 respectively, would give too high figures for deaths accompanied by birth trauma; on the other hand, the absolute figures 15 and 33 would be too low.Taking the figures 15 and 33 as minima a comparison can be made of the risk of death with birth trauma among the premature and the full-term infants.Of the forty-eight cases of birth trauma (spontaneous birth), fifteen were among the premature, the total number of whom can be estimated. The proportion of premature among all births is calculated variously as round about 3.5 %. The number of spontaneous births among the 16,130 is given as 14,000 in round figures by Nevinny. Thus, not allowing for the slight difference there may be in the percentage 3.5 for spontaneous births only, the premature would number 490, and the full-term 13,510.The proportions of deaths with birth trauma are, then, 151490, or 3.1 yo, among the premature, and 33/13,510, or 0.24 yo, among the full-term. The former percentage is thirteen times the 1atter;'hence the risk of death accompanied by birth trauma of the central nervous system is very much greater for premature than for full-term infants.

SOME FACTORS ASSOCIATED WITH PREMATURITY part II.

“…Since 71 per cent of babies weighing 54 pounds or less were premature by length of gestation as well as by birth-weight, it can be estimated that 4.3 per cent of legitimate single births satisfy both these standards of prematurity. A recent study of 226 babies delivered in University College Hospital (Karn, 1947) shows that 3.5 per cent were premature by both standards, and this percentage does not differ significantly from the maternity survey estimate. Table IV relates the alleged duration of pregnancies resulting in premature delivery to the weight of the babies at birth.…”

“…This standard was first suggested in 1919 by Ylppo and has since been generally adopted, although it is by no means an exact index of an abnormally short gestation period. It would, however, be just as unreliable to use duration of pregnancy as the measure of prematurity for, on the one hand, there may be great difficulties in establishing the date of conception and, on the other, normal pregnancies vary greatly in length ; according to Karn (1947) the limits of normality are 247 and 317 days with a mean of 278 days.…”

Observations on all Births (23,970) in Birmingham, 1947 : II. Birth Weight

“…Among larger series are those of Pearson (1900;1914), Zangemeister '(1917), Bruce Murray (1924), Martin (1931), Anderson and others (1943), Karn (1947), and Hosemann (1948), all on hospital populations. Perhaps the most representative is that of Anderson and others, since it was assembled in a city (Cincinnati) in which there were few facilities for deliveries at home.…”

Relative Weight Deficiency in the Newborn

“…A n u m b e r o f stu d ies h av e ap p eared in recent y ears concerning relativ e w eight deficiency in th e new born an d th e crite ria for distinguishing t h a t group from th e to ta l n u m b e r o f p re m a tu re babies [1,2,3,4,5].…”