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The Duration of Human Nancy

days, illness, time, months, nine and conception

THE DURATION OF HUMAN NANCY.

The process going on within the body of the mother in the production of offspring is called gestation, and the whole time occupied by the process is called the period of gestation. In the human being the length of this period, that is, the average duration of pregnancy, is between 274 and 280 days, or about forty weeks. It is roughly counted as nine calendar months. This period should be estimated from the time of conception to the time of birth. But the time of conception, that is, the time when the male element meets the ovum and enters into it, it is impossible to learn, for the period of conception is not necessarily the same as the period of sexual intercourse. The ovum may be fertilized even before it has left the ovary, or in any part of its course down the fallopian tube before reaching the womb. Conception may not take place thus for several days after intercourse, or it may take place shortly after intercourse, according to the distance the sper matic fluid has to travel before reaching the ovum, The time is, therefore, dated from the end of the last monthly illness, and the usual course is to count 280 days from the kit day of the last illness.

While 280 days have been mentioned as the ordinary duration of human pregnancy, there is good reason for believing that very consider able variation in the length of time may occur and yet the pregnancy be a perfectly natural one. Cases are on record where the only possible conclusion was that pregnancy had extended to 295 days. In Scotch law, and ac cording to the French Code, the utmost limit is 300 days.

Probable Date of' tion is believed usually to occur about a week after the end of the last illness; the duration of pregnancy is counted as nine calendar months, so that the time of confinement is likely to occur nine months and one week from the last day of the last illness, that is, about 280 days.

This supplies a ready method of counting. From the last day of the last illness reckon nine months forwards, and add seven Thus, a woman ceased to be ill on the 7th January ; nine months forwards gives the 7th October, and adding seven days we have the 14th October as the probable date of delivery. A shorter method is to count three months back instead of nine months forwards, and then add the seven days. Thus three months back from 7th January is, of course, 7th October, and seven days gives 14th October as before. As another example, suppose the 10th February to be the last day of the last illness, three months backwards gives the 10th November, and add ing seven days we get November 17th as the probable date of confinement.

This method of counting is based on the fact that, as a general rule, the monthly illness ceases during pregnancy. But the ovum that becomes fertilized may not be the one whose ripening was at the time of the last monthly illness, but it may be the ovum of the succeed ing month, whose maturing was not attended by the monthly discharge, because conception had occurred. That is to say, conception may have occurred either within a few days after the last illness, or immediately before the suc ceeding illness was due. This gives a difference of three weeks. If, then, one has accurately known the last day of the last monthly illness, and has properly counted 280 days (or nine months and seven days) from that time, and if the confinement does not occur within a week after the estimated date, it may be expected not to take place for an additional fortnight, that is, altogether, three weeks after the origi nally fixed date.