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Demography 359
18. It is believed that genital diseases are responsible for the high infertility
rate in some of the developing countries. But setting aside such environmental
influences, a fact remains which has not yet been explained. How is it that out
of the 750,000 odd ovules9 present at the birth of a woman only a few hundred
are used for fecundation purposes? And to what sort of ‘ageing’ process are
those ovules subject? Obviously, the ovules which remain capable of being
fertilized deteriorate in ‘quality’ as the mother grows older, as witness the
increasing incidence of still-birth and congenital defects with the mother’s ad-
vancing years. Lastly, how is it that this ageing process comes to an inevitable
end towards the age of fifty? Here we have a whole field open to research in
the coming years.
The spacing of births
19. Let us now turn to the women who remain fertile at the end of their preg-
nancy. It has been observed that they only regain their fertility after a certain
lapse of time. A dead period intervenes in the production of progeny. While,
however, we know that this dead period exists, we do not yet know much about
the duration and causes of this temporary infertility and, here again, paradoxi-
cally enough, we know more about the populations in the developing countries
than we do about those in the industrialized countries. It is known that breast-
feeding plays a part in it. For the time being, all we can do is to observe the
effect of this in a collectivity. It can be stated, for example, that in a population
where all the women breast-feed their children for, say, two years, the interval
between births is increased by about 30 % as compared with a population where
breast-feeding is not practised. But we are not able to identify in advance those
women who wil remain sterile; which means that the action exerted by breast-
feeding on fertility is far from being understood. Genetic factors are certainly
involved.
20. Let us place ourselves at the moment when the dead period ends and observe
what happens. We wil suppose that the couples do not practice contraception.
The woman is going to become pregnant within a certain time which wil depend
on two factors: the frequency of sexual intercourse and the proportion of ovules
of ‘sound‘ quality. Indeed, it appears that, even in the case of a fertile woman, all
the ovules are not capable of being fertilized. The woman continues to produce
ovules, which is why she is not relegated among the henceforth infertile women.
But from time to time she produces ovules that are not able to be fertilized. This
amounts to a sort of temporary infertility, but which is not bound up this time
with any preceding pregnancy. The corresponding menstrual cycles may even
be anovular, presenting all the characteristics of normal cycles, except for the
presence of ovules. Such explanations are only the reflection of our ignorance.
We know that something happens, but we do not know the mechanism. It is
essential for the demographer to know whether the cycles during which fecunda-
tion is impossible occur at haphazard intervals or whether they occur in a
series.