The number of children to which during the three decades of her sexual life, from the menarche to the menopause, a woman might theoretically give birth, is never actually born. If we assume that, during the period of active sexual life, a woman requires a period of fifteen months to two years for each pregnancy, parturition, and lactation, a woman could easily during this period have fifteen or sixteen children, and this figure would represent the normal product of the normal fertility of the human female. There are indeed, women who, it may be in consequence of an exceptionally long period of sexual activity, or through giving birth repeatedly to twins or triplets, or because they have married several husbands in succession, have given birth to twenty-four children or even more. In Berlin, in the year 1901, there lived a woman 41 years of age who had had 23 children; there were three women, aged respectively 40, 43, and 46 years, who had had each 21 children; 246 women with families numbering 13 to 20; and 169 women each of whom had given birth to 12 children. In the very great majority of cases, however, the fertility of the wife of the present day is never fully developed. It is modified in various ways by the conditions of marriage, by social circumstances, by considerations relating to the health of husband or wife, by actual illnesses, and by voluntary limitation of fertility. Generally speaking, according to the investigations of Quetelet, Sadler, and Finlayson, the fertility of women is greatest in marriages in which the husband is as old as the wife, or a little older, but without marked difference in age. Marriages contracted at a very early age are less fruitful; the highest fertility is found in marriages contracted when the husband is 23 and the wife 26 years of age.
Conception does not generally take place until sexual intercourse has been frequently repeated. As the result of a statistical enquiry of my own, relating to 556 fruitful marriages, I ascertained that in these the first delivery occurred:
Within 10 months after marriage in 156 cases.
Within 11 to 15 months after marriage in 199 cases.
Within 16 to 24 months after marriage in 115 cases.
Within 2 to 3 years after marriage in 60 cases.
More than 3 years after marriage in 26 cases.
Thus we learn that in 35.5% of the cases the first delivery occurred within 1¼ years after marriage; in 15.6% within 10 months; and in 19.9% within 15 months after marriage; and 11.5% of the cases, the first delivery was more than 1¼ years and less than 2 years after marriage; in 6.0% it was between 2 and 3 years after marriage; and in 2.6%, the first delivery did not occur until more than 3 years after marriage.
From examination of the birth registers of Edinburgh and Glasgow, Matthews Duncan determined the mean interval between marriage and the birth of a living child to be seventeen months. In the majority of cases, the first delivery does not occur until a complete year has elapsed since marriage; in fact, in nearly two-thirds of the instances the first delivery occurs during the second year of married life.
The interval between two successive births is, according to Matthews Duncan, on the average 18 to 24 months, according to Goehlert, 24 to 26 months; the latter, however, points out that in cases in which the child dies very soon after birth, the birth of the next child ensues on the average in 16 to 18 months. In this connection, we must not fail to take into consideration the influence of lactation, inasmuch as mothers who do not suckle their children become pregnant considerably earlier, on the average, than those who undertake this duty. In reigning families, for instance, it is by no means uncommon for the consort to be delivered twice within a single year. The degree to which lactation hinders conception is so widely known, that women often suckle their infant for a very long period, with the definite aim of preventing the speedy recurrence of pregnancy. A high official from the Dutch Indies informed me that for this reason the native women were accustomed to suckle their infants for several years, and that it was by no means uncommon to see a small boy running about smoking a cigar, and then hurrying to his mother in order to be suckled.