The thickness and density of the uterine parietes form two of the most remarkable changes of pregnancy. The non-gravid uterus has already been described as having very thick walls. After fecundation, these walls maintain usually the same relative thickness; although as the uterus itself increases in size, its parietes becomes less dense, and, instead of being hard and fibrous, are said by Cazeaux, to have a clammy softness, closely resembling that of caoutchouc softened by ebullition, or that of an oedematous limb. “It is now known that the womb preserves nearly the same thickness during the whole course of pregnancy, as it had when unimpregnated. This thickness, which is greater at the insertion of the placenta, generally diminishes from the fundus towards the cervix, where it is frequently found to be more than two or three lines or even less. It increases a little in all parts of the organ at the same time, until the third or fourth month, and then remains rather below its primitive limits, to exceed them again in the last stages of pregnancy, except the cervix, which at that period especially grows thinner.
Structure. The immense enlargement of the womb, from its nongravid size up to to that capable of enclosing one foetus or even more at full term, can only be the result of a very great increase in its entire mass. But this great development in substance, in which the weight of the uterus comes to be reckoned by pounds instead of by ounces, is accompanied with a corresponding development of its proper organization. In its non- gravid condition the uterus exhibits only the type of the wonderful development which it acquires in pregnancy, and which is essential to the proper performance of the important functions with which it then becomes charges, “Its fibres, which were pale, dense and inextricable tangles, soften, become redder and soon represent layers and bundles easy to detect and to follow. The cellular tissue, which was before so firm, dense and elastic, relaxes, becomes supple, and indeed resembles the common cellular tissue, and in this way permits the other elements which it held in bondage, as it were, to follow the impulse that animates the whole womb. The arterial branches, folded upon each other like the vas deferens, and bridled in this condition by dense elastic lamina, yield to the general relaxation, and gradually become lengthened; their angles at first so sharp, with their doubling, grow blunter, enlarge, and at last exhibit only certain zigzags of greater or less depth, tortuousities which do not impede the circulation.
The veins undergo the same metamorphosis: already, in the natural stage, larger and less tortuous, they are enlarged and developed still more rapidly than the arteries; afterwards they are observed to furrow the fleshy layer in every direction, and form a net-work which in some measure separates it into two planes. They are large enough to admit a goose-quill, and in some instances the end of the little finger; near the mucous membrane they dilate so as to constitute cones with inverted bases, which were first termed uterine sinuses, but which are now called venous sinuses. Velpeau.
The lymphatic vessels and the nerves are also enlarged in a corresponding manner in pregnancy. The great change in the texture of the mucous lining membrane of the uterus has already been referred to in describing the formation of the decidua. All the component tissues of the body of the uterus receive accessions both in structure, size and physiological activity, to correspond with the new and most important functions which this organ is called upon to discharge in pregnancy and gestation.
THE CERVIX UTERI is also subject to certain changes during the period of gestation. These occur simultaneously with those already described as affecting the body of the womb; and are the results of the physiological action by which the entire uterus becomes adapted to its new functions. In the consistence of its tissue, in its volume, form, situation and direction, the cervix uteri becomes changed in a remarkable manner; and these changes, so far as they are appreciable, afford valuable indications for determining the fact and the stage of pregnancy.
Softening of the tissue constitutes the principal modification of actual structure of the cervix uteri. The change from a firm, fibrous structure to that of a soft, fungus-like substance, begins as the lower border of the interior surface of the os tincae, in the first month of pregnancy; and increase from within outward, and from below upwards, till at the sixth month this softening embraces the whole thickness of the lips of the o tincae and the lower half of the sub-vaginal portion of the cervix. This softening of the tissue is always from below upwards, and proceeds also. pari passu with the development of the fundus. And so exactly is this proportion maintained that an experienced examiner can always determine with very great accuracy the advancement of the pregnancy by noting the extent of this upward softening in the cervix uteri. It must be borne in mind, however, that in those who have had several children, the sub-vaginal portion of the neck of the uterus loses a considerable portion of its length; otherwise the briefer extend of the softening in such cases might mislead the examiner to conclude that the pregnancy was less far advanced than it really was. So also in cases of first pregnancy, since this softening of the cervix uteri is less strongly marked, and more slow in its development, and therefore more difficult of detection, these circumstances should always be taken into consideration in forming a conclusion is such cases.
The increase in volume of the cervix uteri goes on in equal ration with decrease in the density of its substance. But the cervix does not shorten, the description given from Velpeau, on a previous page, of the development of the fundus at the expense of the cervix, is applicable only to the last fortnight of utero- gestation. On the contrary, the length of the cervix may begin to increase a little after the commencement of the fifth month; and this elongation, which previously had been rather apparent than real, is continued till the final absorption of the cervix itself in the fortnight immediately preceding parturition. At his period, the whole neck having become softened and thickened, becomes more easily distensible; and the development of the body of the uterus form above downwards meets the softening and development of the neck from below upwards, at this juncture, which is at the as internum; and the complete fusion of the fundus with cervix takes place, and the cavity of the womb is one from the fundus to the os tincae or os externum. This fusion causes the sinking down of the fundus from thee pit of the stomach, so often observed in the last weeks of gestation; the fundus must sink as the walls and lower segment of the uterus are expanded. And upon the occurrence of this depression the female breathes freer and feels in all respects.
The form of the cervix uteri differs in the multiparae from what is observed in the primiparae, this difference is principally to be noted in the varying size and shape of the os tincae and of the cavity of the cervix itself. In the primiparae, the os tincae changes from a simple transverse fissure to a circular depression. The cavity from being conical, becomes spindle=shaped; and the softening of the externally constricted os will allow the finger to penetrate into the cavity. The os tincae never been ruptured by parturition, its mucous lining membrane rounds if off very nicely; and none of the inequalities, fissures or puckerings so common in the multiparae, are to be found here.
diagram
A section showing the neck of the uterus; the anterior and posterior lips are seen in situ, being separated from each other by the fusiform cavity in the neck.
In the multiparae the numerous cicatrices and indentations render the os tincae more originally patulous; and the most noticeable effect of the pregnancy upon the orifice in such cases is to cause it to be more easily dilatable. And as the gestation progresses, this dilatibility of the os tincae becomes and actual spreading out of the inferior portion of the cervix, until it reaches the middle part of the cervix uteri about the seventh month, and nearly gains the internal orifice by the ninth month. The cavity of the cervix goes on enlarging simultaneously with the softening of its walls and the advance of pregnancy. And the opening and cavity become thimble-shaped, admitting the finger farther and farther into it, as the pregnancy advances.
The gradual change in the opening of the os tincae and dilatation of the cavity of the cervix, may be seen in the accompanying cuts upon the next page. In the preceding account of the changes in the neck the uterus incidental to pregnancy, we have principally followed the very excellent, and in some respects entirely original, account given by Cazeaux; and for the following summary of these changes, we are indebted to the same author.
