Fig. 9.—The usual position of the baby just before he is born.
The average normally developed baby has grown to a length of about 20 inches and weighs about 7¼ pounds, boys usually being about three ounces heavier than girls, but there may be a variation of weight among entirely normal, healthy babies from a minimum of 5 pounds to as high as 11 pounds or more. Newborn babies very seldom weigh more than 12 pounds, in spite of legends and rumors to the contrary.
The size of the baby is affected by the race of his parents; colored babies, for example, averaging a smaller weight than white babies. And, as might be expected, the size of the parents is likely to be reflected in their infants, large parents tending to have large children and vice versa.
The number of children which the mother has previously borne is also a factor, since the first child is usually the smallest, the size of those following showing an increase with the mother’s age up to her twenty-eighth year, if her pregnancies do not occur at too frequent intervals.
Twins. Sometimes a woman gives birth to more than one baby at the same time. When there are two they are called twins; triplets when there are three; quadruplets, quintuplets and sextuplets respectively, when there are four, five and six babies within the uterus at once. Six is the largest accredited number on record.
It is estimated that twins occur once in ninety pregnancies and triplets once in about seven thousand cases. The tendency seems to be inherited, as is evidenced by the number of twins and triplets to be found among relatives.
Twins are often prematurely born and each is likely to be smaller than a baby resulting from a single pregnancy, but their combined weight is greater than the weight of one normal baby.
Extra-uterine Pregnancy. Another departure from the normal pregnancy is when the baby develops outside of the uterus. Although in the normal course of events the fertilized ovum travels down the tube and becomes attached to the uterine lining, it is possible for it to stop, and more or less completely develop at any point along the way. This is called an extra-uterine pregnancy, since it occurs outside of the uterus. If the baby develops in one of the ovaries, it is termed an ovarian pregnancy, and a tubal pregnancy if it develops in a tube, this being the most frequent variety of extra-uterine pregnancies. Only about one out of a hundred such pregnancies continue throughout the allotted period, and accordingly, a live baby, capable of living for any length of time, seldom results.
To sum up a normal pregnancy, we find that in the course of ten lunar months following the fertilization of an ovum, the uterus grows from a small, flattened pelvic organ, 3 inches in length, to a large muscular sac, about 15 inches long occupying the abdominal cavity. It increases its weight sixteen times, that is, from 2 ounces to 2 pounds, while the capacity of the uterine cavity is multiplied five hundred times. Within the uterus is a baby weighing about 7¼ pounds; a placenta weighing perhaps 1¼ pounds and approximately a quart of fluid. The baby is attached to the placenta by means of a jelly-like cord about as thick as one’s first finger and 20 inches long; baby, placenta, cord and fluid all being contained in a thin, but strong sac frequently called the bag of waters, but by the doctors termed the membranes. The total weight of the uterus and its contents at the end of pregnancy is usually about 15 pounds.