As a rule, a woman has one child at a time. Twins, when they occur, are looked upon with disfavor by most people. There is a popular notion that they are apt to be wanting in physical and mental vigor. This opinion is not without foundation. A careful scientific examination of the subject has shown, that of imbeciles and idiots a much larger proportion is actually found among the twins born than in the general community. In families where twinning is frequent, bodily deformities likewise occur with frequency. Among the relatives of imbeciles and idiots, twin-bearing is common. In fact, the whole history of twin-births is of an exceptional character, indicating imperfect development and feeble organization in the product, and leading us to regard twins in the human species as a departure from the physiological rule, and therefore injurious to all concerned. Monsters born without brains have rarely occurred except among twins.
The birth of twins occurs once in about eighty deliveries. A woman is more apt to have no children than to have more than one at a time. In view of the increased danger to both mother and child, this rarity of a plural birth is fortunate.
WHY ARE TWINS BORN?
What are the causes or favouring circumstances bringing about this abnormal child-bearing? For it is brought about by the operation of laws. It is not an accident. There are no accidents in nature. By some it is supposed to be due to the mother, by some to the father. There are facts in favour of both opinions. Certain women married successively to several men have always had twins, while their husbands with other wives have determined single births. Certain men have presented the same phenomenon. We can scarcely cite an example more astonishing than that of a countryman who was presented to the Empress of Russia in 1755. He had had two wives. The first had fifty-seven children in twenty-one confinements; the second, thirty-three in thirteen. All the confinements had been quadruple, triple, or double. A case has come under our own observation in which the bearing of twins has seemed to be due to a constitutional cause. The wife has nine children. The first was a single birth, a girl; the others were all twin-births, and boys.
It has been asserted that compound pregnancies are more frequent in certain years than in others. But that which seems to exert the greatest actual influence over the production of twins is the age of the mother. Very extensive statistics have demonstrated that, from the earliest child-bearing period until the age of forty is reached, the fertility of mothers in twins gradually increases. Between the ages of twenty and thirty, fewest wives have twins. The average age of the twin-bearer is older than the general run of bearers. It is well known that by far the greater number of twins are born of elderly women. While three-fifths of all births occur among women under thirty years of age, three-fifths of all the twins are born to those over thirty years of age. Newly-married women are more likely to have twins at the first labour the older they are. The chance that a young wife from fifteen to nineteen shall bear twins is only as one to one hundred and eighty-nine; from thirty-five to thirty-nine the chance is as one to forty-five,—that is, the wives married youngest have fewest twins; and there is an increase as age advances, until forty is reached.
Race seems to have some influence over plural births. They occur relatively oftener among the Irish than among the English.
INFLUENCE OF TWIN-BEARING ON SIZE OF FAMILIES.
Do women bearing twins have in the end larger families than those never having but one at a time? Popular belief would answer this question in the affirmative. Such a reply would also seem to receive support from the fact, well established, that twins are more frequently additions to an already considerable family than they are either the first of a family or additional to a small family. But statistics have not answered this question as yet positively. They seem, however, in favour of the supposition that twin-bearing women have larger families than their neighbors.
Women are more apt to have twins in their first pregnancy than any other, but after the second confinement the bearing of twins increases in frequency with the number of the pregnancy. It becomes, therefore, an indication of an excessive family, and is to be deplored.