The Embryo : Part 2

The Prospective Mother: A Handbook for Women During Pregnancy
by J. Morris Slemons

(Page 5 of 18)

For the present, the second question cannot be answered with equal assurance. More than five hundred theories have been offered to explain the relation of sex; nearly all of them have no reasonable foundation and are only of historical interest. The view that girls are derived from the right ovary, boys from the left, has long since been disproven, and deserves mention merely because the laity still believe it. Happily, during the last few years, observations and experiments have been made which greatly advance our knowledge of the subject and give promise of an early solution of the problem. The controlling factor in sex determination has been narrowed down to three possibilities; it is inherited either from the single cell contributed by the father or from the single cell contributed by the mother, or it is determined by the effect these two cells have upon each other at the moment when they unite. In most animal species the weight of authority distinctly favors placing the whole responsibility upon the male cell.

According to recent evidence, there are two kinds of male germinal cells; one kind giving rise to female offspring and the other to male. In all probability, at the time of the marital relation, these varieties are deposited in the vagina in equal numbers; and, moreover, the mode of their production is such as to place absolutely beyond human control the possibility of changing this ratio. Since only one spermatozoon enters the ovum, whether or not the child will be a boy or a girl depends entirely upon which type gains entrance. If this explanation is correct, and it is in accord with careful biological observations, it removes from the mother all responsibility for the sex of her child. Furthermore, since the facts indicate that male-producing and female-producing spermatozoa are present in equal numbers, it follows that practically there is an even chance that an embryo will develop into a boy or a girl.

Birth statistics bear out this conclusion, as data gathered from many countries indicate that when long periods of time are studied 105 boys are born with a surprising regularity for every 100 girls. Thus, the records of Berlin, Germany, for a hundred years show that the maximum difference occurred in 1820, when the males outnumbered the females by 4.79 per cent.; the minimum difference, which was noted in 1835, was .64 per cent. in favor of boys.

No inquiry is more often submitted to the physician by prospective mothers than this, "Can you tell me if my baby will be a boy or a girl?" He cannot. Many rules, to be sure, have been advocated as safe guides toward reaching the correct answer; every midwife possesses her individual formula which she has "never known to fail." But the boastful success depends upon the application of some such method as the following, which I have heard my teacher, Dr. J. Whitridge Williams, expose to his classes. The patient is asked if a boy or girl is desired. She confesses, and is then informed that the sex of her child will be the opposite of her wish. When this guess proves to be correct, there is no doubt of the prophet's wisdom; when it is not, his honor is protected, for the parents have had their hope fulfilled. Their happiness makes them forgetful that the guess was wrong, or, for that matter, that it was ever made.

It was once believed that the sexes might be distinguished before birth by the number of heart beats occurring within a minute. In a general way, the action of this organ in females is somewhat more rapid than in males; and so it was thought that a rate of 144 or more indicated the female and a rate of 124 or less the male sex. But experience has taught that this rule leads to accurate prophecy in no more than half of the cases. As a matter of fact, no means of definitely foretelling the sex of the child has been discovered, and I doubt if it ever can be.

Twins. As every one knows, pregnancy commonly terminates with the birth of a single child. Twins appear in approximately only one of ninety pregnancies, while triplets are extremely rare. It is true that even quintuplets may occur, though up to 1904 only 29 authentic instances could be collected from the whole range of medical literature.

Twins are most frequently born to parents whose ancestors have established this tendency; the trait is usually inherited from the mother's family, though occasionally it is passed on through the father. Of course, that does not explain the cause of twins, which in reality may result from either of two circumstances. More commonly their genesis depends upon the ripening of two eggs at about the same time and the fertilization of both by two different spermatozoa. The children, in this instance known as double ovum twins, may be of the same sex or not. On the other hand, single ovum, or identical, twins are always of the same sex; this follows, since but one egg and but one spermatozoon are here concerned. The incident permitting twins to develop from a solitary ovum must occur soon after conception has taken place. It will be remembered that the first step in the development of the fertilized ovum consists in its dividing into two cells. Ordinarily, both these take part in the development of one embryo, but occasionally they separate and give rise to two. Frequently, the presence of twins can be recognized during the latter months of pregnancy, and accurate means are known of determining after they are born to which variety any given pair belongs.

The Rate of Growth. When we recall the definite and often marked differences in the physical character of women, such as weight and height, it is surprising to learn that the prenatal development of their children proceeds with uniform speed. One very practical result is that the physician is thus enabled, at the birth of a premature infant, to estimate accurately the period of its development. Various criteria, some of which are easy of application, aid in this determination. For example, the length of the child is practically constant for each of the ten lunar months into which the whole gestation period is divided; if, therefore, the length of the newborn infant is known, the stage of its development can always be inferred. From the fifth month the calculation is especially simple, since the length measured in centimeters divided by the figure 5 gives the month to which pregnancy has advanced. Similarly, we can infer the period of development from the weight, though the calculation is more intricate and the method less reliable, inasmuch as the size of the child in the latter months varies somewhat according to the weight of its mother.