Ordinarily the fluid ejaculated by the male must reach the uterus, and in some way be conveyed to the ovaries through the Fallopian tubes to produce fecundation.
It is believed that, as the consequence of copulation, the semen is thrown on the neck of the uterus; that it is carried forward, first, by the movements proper to the uterus and tubes; second, by the movements proper to the spermatozoa till it reaches the ovum, generally in the ovary; that it enters the ovum, and that then fecundation takes place.
Upon being impregnated and the vesicle bursting, the ovum is grasped by the free extremity of the Fallopian tubes, which is in contact with the ovary, the ovum passes from the ovary to the canal, is pressed onwards by the peristaltic motions of the tube through the duct, and finally reaches the uterine cavity; there it continues to grow during the ordinary term of gestation. After two hundred and seventy days the ovule has developed into a child, and is expelled through the natural parts of generation. When gestation proceeds in this manner, it is said to be normal, or good, or uterine; sometimes (though very seldom) the ovule is arrested at some point in its passage, and is developed outside of the womb; this is termed an extra uterine pregnancy.
The time at which conception is most likely to occur is that immediately following the flow of the menses; it may take place immediately before the flow, and sexual intercourse may be fruitful even when it takes place in the middle of the interval between the sexual periods, though the latter is unusual.
When conception takes place a few days or a few hours before the period, it is not followed by the menstrual flow.
UTERO-GESTATION.
At each menstrual period the bulk or size of the uterus is for the time increased, and if conception takes place about that time, the excitement maintains and soon increases the enlargement. The mucous membrane becomes almost doubled in thickness, and when the ovule arrives in the womb, it finds it filled with the membrane, the whole uterus is congested, its vessels enlarge, and are filled with blood, many which were invisible before are now filled with red blood, and the whole form an intricate network on the surface, and in the substance of the organ; the coats of the arteries increase in thickness; the coats of veins are thinner, and admit of still greater distention; the nerves increase in size, and may be seen accompanying the blood-vessels, and there are changes not only in the volume, but in the shape, situation, direction, and relations of the uterus.
The organ increases slowly in size during the early. months of pregnancy, and more rapidly in the later. The walls are distended, however, not mechanically from the development of the ovum, but simultaneously with it, and from a physiological cause; in shape it becomes rounder, and towards the end of pregnancy it has an ovoid form. Simultaneously there is an alteration in its position; at first the neck subsides towards the floor of the pelvis; the presence of the rectum may incline the fundus to the right and the neck to the left; about the fourth month the uterus rises above the superior strait; at four months the fundus uteri is two or three fingers in breadth above the pubis; at five months it is within one finger’s breadth of the umbilicus; between the fifth and sixth month it passes the umbilicus; at seven months it is three fingers’ breadth above the naval; at eight months it is four or five above, but it does not rise higher during the last month. While it is rising it follows the direction of the axis of the superior strait; afterwards it inclines to the right oftener than to the left.
At term, the superior part of the uterus is in contact with the abdominal walls usually, but sometimes there may be some of the intestines interposed between them.
At full term the parietes of the womb are thicker than in the unimpregnated condition; at the point corresponding to the insertion of the placenta, thinner at the neck, and otherwise it retains about its original thickness.