The Determination of Sex
All human cells contain 44 chromosomes plus two sex chromosomes, giving a total of 46 in all. The 44 normal chromosomes affect the structure and function of the body and are responsible for all its hereditary characteristics. The normal female cell contains two sex chromosomes, both of which are X chromosomes. These are responsible for all the female characteristics and are denoted as XX. The normal male cell contains two sex chromosomes of which one is an X chromosome and one is a Y chromosome, and they are denoted as XY. The ovum consists of 22 chromosomes plus one sex chromosome which must be an X chromosome. Sperms each contain 22 chromosomes plus one of the sex chromosomes, which may be either an X or a Y chromosome. The human male cell containing 44 chromosomes plus XY divides to form sperms each with 22 chromosomes plus either X or Y. Obviously the same number of sperms containing X and Y chromosomes are formed. If the ovum is fertilized by a sperm which contains 22 plus X chromosomes, then the offspring will be 44 plus XX, which is female. If on the other hand the ovum is fertilized by a sperm containing 22 plus Y chromosomes, the offspring will be 44 plus XY, which is male.
The sex of the child is, therefore, entirely a male responsibility and no woman should ever apologize or feel sorry for failing to produce a child of the sex her husband wanted. The mother cannot influence the selection of X or Y containing sperms. An escape clause is possible because some people believe that women have a method of differentiating between ‘male’ and ‘female’ sperms, but this has not been proved.
Predestination of Sex
There is no scientific evidence that the production of male or female children may be an hereditary phenomenon. It is appreciated that some families produce a long list of males whilst other families produce a large number of female children, but nevertheless statistically each pregnancy stands an equal chance of being male or female and any long run of one sex is entirely fortuitous. It may well be that the present state of our knowledge is incomplete and that eventually some factor will be discovered which does show why some families are predisposed to produce one sex.
One very interesting factor about sex determination is the repeated production of male children by the sub-fertile couple. This is particularly noticeable when the male is the sub-fertile partner and tends to support the old adage that ‘anyone can produce a son but it takes a real man to produce a daughter’. The reason for this is not known.
X and Y chromosomal sperms are produced in equal numbers and, despite many popular theories, there is no certain method of separating X from Y and thus deciding the eventual sex of the child. A lot of experimental work has been done on this problem with a certain amount of success in the veterinary world, where the predetermination of sex is of more value than in humans. Experiments have been conducted using human sperms and it has been suggested that passing an electric current through seminal fluid will separate ‘male’ and ‘female’ sperms so that the sex can then be selected for artificial insemination, but this is not, at present, a practical proposition.
The various theories regarding what should be done to produce either a male or a female child are not supported by scientific evidence. Theories such as the time in the menstrual cycle, or the time at night at which intercourse should take place, or that a male child is born when ovulation coincides with a particular phase of the moon, are without foundation. There is no realistic way as yet by which sex can be predetermined in the human. Various methods have been used throughout history and it is commonly thought that an acid medium will predispose to male fertilization. While this may be true, there is no medical evidence to support it. For centuries grand ladies in various countries have douched with a variety of acid mixtures from vinegar to lemon juice prior to intercourse, in the hope that this will allow them to conceive a male child. Since the fertilizing sperm must gain access to the cervical canal in order to survive and the mucus in the canal of the cervix is uninfluenced by vaginal douching, the argument for this is not very strong. It is weakened even further when it is appreciated that the normal acidity of the vagina is much greater than that of either dilute vinegar or lemon juice. Similarly, the taking of acid or alkaline diets and medicines will not help.
Many non-medical, and some medical, authorities believe that the ‘male’ and the ‘female’ sperms have different characteristics, especially regarding their motility and their ability to survive, and that these properties can be utilized to preselect sex in 80 per cent of people. Some consider that they have ample evidence to prove this.
Prenatal Determination of Sex
There is no way in which the sex of the unborn child can be accurately determined without some danger to the foetus. The only certain method of finding out the sex of the unborn child is to withdraw some of the fluid surrounding the baby by a process known as amniocentesis. The cells which it contains are stained by a special method and then carefully examined under the microscope. If the XX chromosomes are present they form a characteristic stain within the nucleus of the cell, known as a Barr body, which can be seen when the cells are examined under the microscope. By this method it is possible to determine the sex of a child with 100 per cent accuracy at any stage after about the 12th week of pregnancy. Examination of the baby’s cells is used only for definite medical indications because it does present a slight hazard to the unborn baby, as well as to the mother. It is not used unless the advantages of the knowledge obtained outweigh the disadvantages. At the time oi writing it is not considered that the satisfaction of curiosity regarding sex is an adequate excuse for performing amnio¬centesis. The only exception to this is where the infant may be thought to suffer from mongolism or a sex-linked disease such as amyotonia congenita, when abortion may be considered.
X-rays will not determine the sex of a child in utero because simple X-rays only outline the bones.
Counting the baby’s heart rate in the uterus is probably the simplest and most accurate method of determining sex. The normal heart rate is between 120 and 160 beats per minute. A heart rate which is persistently below 140 beats per minute is usually male, whereas one which is persistently above 140 beats per minute is usually female. The foetal heart should be counted before the foetus has been disturbed by examination. This method is, however, only about 70 per cent reliable and the expectant mother is advised against choosing the colour of her layette on the results.
Suspension of an object on the end of a piece of string over a pregnant uterus is believed by many people to give an indication of the sex. When the object moves in a clockwise direction the child is said to be male and if it moves counter clockwise it is said to be female.
There are many other methods, according to folk lore, of assessing the sex of the infant, including the time at which movement is first felt, the shape of the abdomen, the amount of nausea and sickness and the occurrence of nose bleeds.
There is a certain amount of medical evidence that the female baby produces a greater effect upon its mother than does a male baby and that the carrier of a female child will, therefore, suffer from more nausea and sickness and will ‘ feel more pregnant ’ than the carrier of a male child. A woman who may even be unaware of the fact that she is pregnant except for the absence of her menstrual period is more often carrying a male child.
Although parents all over the world are always anxious for any indication of the sex of their unborn child, the majority of them would, in retrospect, prefer not to know the answer till the child is actually delivered. It would be rather an anticlimax if the sex of the child were known for months before delivery.
Boy : Girl Ratio
More male children are delivered than female children. The ratio is 106 boys to every 100 girls. It is considered that the incidence of male pregnancies at conception is even greater than this, a ratio of about n 3 male to 100 female, but the preponderance of male babies is reduced because of the higher incidence of miscarriage amongst the male conceptions. The reason for the higher incidence of male conceptions is not known. The ratio of males to females varies slightly with different races and in different geographic areas.