CHAPTER V
SIGNS, SYMPTOMS, AND PHYSIOLOGY OF PREGNANCY
Signs and Symptoms of Pregnancy. Unfortunately for all parties concerned, the exact duration of pregnancy has never been ascertained, since there is no way of knowing when the ovum is fertilized, the moment which marks the beginning of pregnancy.
It is obviously impossible, therefore, to foretell exactly the date of confinement. But labor usually begins about ten lunar months, forty weeks or from 273 to 280 days after the onset of the last menstrual period.
Thus the approximate date of confinement may be estimated by counting forward 280 days or backward 85 days from the first day of the last period. Or what is perhaps simpler, and amounts to the same thing, one may add seven days to the onset of the last period and count back three months. For example, if the last period began on June third, the addition of seven days gives June tenth, while counting back three months indicates March tenth as the approximate date upon which the confinement may be expected.
This is probably as satisfactory as any known method of computation, but at best it is only approximate, being accurate in about one case in twenty. But it comes within a week of being correct in half the cases, and within two weeks of the date in eighty per cent of all pregnancies.
Another method sometimes employed by obstetricians is to estimate the month to which pregnancy has advanced by measuring the height of the fundus, and thus forecasting the probable date of confinement. It is generally agreed that the ascent of the fundus is fairly uniform and that at the fourth month it is half way between the symphysis and umbilicus; at the sixth month, on a level with the umbilicus; at the seventh month, three fingers’ breadth above; at the eighth month, six fingers above the umbilicus and at the ninth month just below the xiphoid. At the tenth month, or term, the fundus sinks downward to about the position it occupied at the eighth month. (Figs. [31], [32] and [33].)
This method, however, is measuring by months, not days, and leaves a wide margin for conjecture as to the exact date.
Fig. 31.—Height of fundus at each of the ten lunar months of pregnancy.
Still another method is to count forward 20 or 22 weeks from the day upon which the expectant mother first feels the fetus move. As we shall see presently, this experience, termed “quickening,” usually occurs about the 18th or 20th week, but is so irregular that it is unreliable as a basis for computation.