The Prospective Mother | Page 7

the bladder, giving the
same sensation as when the bladder is distended with urine.
Although the presumptive signs which we have considered by no means exhaust the list,
all the others are totally untrustworthy. Each of the more reliable symptoms, as we have
seen, must be accepted cautiously; but taken altogether, except in very unusual cases,
they may be relied upon. _If, for example, menstruation has previously been regular and
then a period is missed, the patient has good reason to suspect she is pregnant; if the next
period is also missed and meanwhile the breasts have enlarged, the nipples darkened, and
the secretion of colostrum has begun, it is nearly certain that she is pregnant; whether
morning sickness and the desire to pass the urine frequently are present is of no
importance._ But the most characteristic evidence, we must remember, is not available
until the eighteenth or twentieth week; then the signs of pregnancy are unmistakable.
THE DURATION OF PREGNANCY.--After the existence of pregnancy has become
assured, perhaps the greatest interest centers about the date upon which the birth may be
expected. Even to approach accuracy in this prediction the prospective mother must be
familiar with certain facts which she will always observe, but which, unless she
appreciates their importance early in pregnancy, she may fail to record or to remember. In
a few cases, however, such exceptional information as knowing the date of conception
does not lead to an absolutely accurate prediction. But the deviation from the rule will be
understood only after we understand the rule itself, which is based upon what we accept
as the average duration of human pregnancy, technically called the period of gestation.
In a broad sense, the period of gestation for each variety of mammal is determined by the
time required for embryonic development to reach the point where the young may live

independently of the mother. This point is reached more quickly with small animals than
with large. The mouse, for example, generally brings forth its young in three weeks,
whereas the pregnancy of the elephant lasts two years. In human beings, counting from
the time of conception to the time of delivery, pregnancy continues approximately 273
days. This number is merely an estimate calculated from hundreds of cases in which there
was no question as to the underlying facts. Individual cases vary notably, and indicate
that two women may become pregnant on the same day and yet not necessarily be
delivered at the same date.
Irregularities in the duration of pregnancy are not limited to man. Thus, while the mean
period of gestation in the rabbit is thirty-one days, it may be either shorter or longer by as
many as eight days. Similar variations occur in the pregnancies of all animals, and are,
moreover, notably greater among larger animals, since for such animals the period of
gestation is relatively long. For instance, the accurate observations of veterinarians
indicate that the mean period of pregnancy in the cow is 285 days from the time of
conception. This fact notwithstanding, a competent observer found that, of 160 cows, 67
were delivered before the 280th day; 68 between the 280th and the 290th day; and 25
after the 290th day. Although nothing unnatural was observed in any instance, the first
animal was delivered 67 days before the last, and in 5 instances gestation continued 308
days.
In ancient times it was believed that the duration of pregnancy was of even more
uncertain length in man than in the lower animals; but since the eighteenth century
thirty-nine weeks have been accepted as the average duration of the human pregnancy
when reckoned from the day of conception. As this date is seldom known, it is most
convenient to reckon from the first day of the last menstrual period. Estimated in this way
its average duration is 280 days. As this period corresponds to ten menstrual cycles,
physicians prefer to describe pregnancy as lasting 10 lunar months of four weeks each.
This is equivalent to 9 calendar months, in terms of which its duration is popularly stated.
THE ESTIMATION OF THE DATE OF CONFINEMENT.--Since pregnancy is not an
absolutely fixed period, we possess no reliable means of predicting the exact day when it
will end. The most satisfactory method of prediction consists in counting forward 280
days from the beginning of the last menstruation or, what gives the same result, counting
backward eighty-five days from this date. _To make the calculation in the simplest way
we count back three months and add seven days_; this addition is made because seven
days generally represents the difference between three months and eighty-five days. If the
last menstruation, for example, began on October 30th, we count back three months to
July 30th and add seven days, which gives August 6th