The duration of pregnancy is generally from 278 to 300 days. At the end of this period, labor or parturition occurs, the process by which the new human being is brought into the world. This process sometimes begins suddenly, but generally gives indications of its approach for some days or at least hours beforehand.

The symptoms of the approaching conclusion are gradually increased irritability of the bladder, with much difficulty in standing or walking, and a change in form of the abdomen which results from the settling down of the womb, leaving the waist smaller, but increasing the prominence of the lower portion of the abdomen a short time before the labor is to begin. Also the external parts become swollen, and there is a leucorrhoeal discharge of a thick, clear matter somewhat resembling the white of an egg. Uterine contractions, quite painless in character, are also indicative of the approaching crisis. These contractions at first occur at irregular intervals. When they become regular, the labor has begun. The pains usually begin in the back and sacrum, and extend to the front part of the abdomen. What are termed false labor pains arise from colic, constipation, or irritation of the bowels. They differ from labor pains in being irregular. The term pain, as used in obstetrics, is applied to the spasmodic uterine contractions which take place, together with the pain incident to the same.

Presentation and Position

The term presentation has reference to the particular part of the body which presents at the mouth of the womb. The term position has reference to the location of the presenting part in the passages of the mother. The most usual presentation is the head. Occasionally the other extremity of the trunk takes precedence, forming what is termed a "breech presentation." In still other cases the body lies crosswise of the outlet, a presentation which must be modified in some way. before the infant can he born

There are various modifications of each of these classes of presentation, that is, other parts of the head may present. In a perfectly natural labor, the vertex of the head is the presenting part. But vari ous other parts of the head may be presented, more or less complicating the process.