The recent investigations of Stengel and Stanton tend to show that the increase of the heart's work during pregnancy is less considerable than has generally been supposed, and that beyond some enlargement and dilatation of the right ventricle there is not usually any hypertrophy of the heart.
The total quantity of blood is raised. While increased in quantity, the blood appears on the whole to be somewhat depreciated in quality, though on this point there are considerable differences of opinion. Thus, as regards hæmoglobin, some investigators have found that the old idea as to the poverty of hæmoglobin in pregnancy is quite unfounded; a few have even found that the hæmoglobin is increased. Most authorities have found the red cells diminished, though some only slightly, while the white cells, and also the fibrin, are increased. But toward the end of pregnancy there is a tendency, perhaps due to the establishment of compensation, for the blood to revert to the normal condition.[[177]]
It would appear probable, however, that the vascular phenomena of pregnancy are not altogether so simple as the above statement would imply. The activity of various glands at this time—well illustrated by the marked salivation which sometimes occurs—indicates that other modifying forces are at work, and it has been suggested that the changes in the maternal circulation during pregnancy may best be explained by the theory that there are two opposing kinds of secretion poured into the blood in unusual degree during pregnancy: one contracting the vessels, the other dilating them, one or the other sometimes gaining the upper hand. Suprarenal extract, when administered, has a vaso-constricting influence, and thyroid extract a vasodilating influence; it may be surmised that within the body these glands perform similar functions.[[178]]
The important part played by the thyroid gland is indicated by its marked activity at the very beginning of pregnancy. We may probably associate the general tendency to vasodilatation during early pregnancy with the tendency to goitre; Freund found an increase of the thyroid in 45 per cent. of 50 cases. The thyroid belongs to the same class of ductless glands as the ovary, and, as Bland Sutton and others have insisted, the analogies between the thyroid and the ovary are very numerous and significant. It may be added that in recent years Armand Gautier has noted the importance of the thyroid in elaborating nucleo-proteids containing arsenic and iodine, which are poured into the circulation during menstruation and pregnancy. The whole metabolism of the body is indeed affected, and during the latter part of pregnancy study of the ingesta and egesta has shown that a storage of nitrogen and even of water is taking place.[[179]] The woman, as Pinard puts it, forms the child out of her own flesh, not merely out of her food; the individual is being sacrificed to the species.
The changes in the nervous system of the pregnant woman correspond to those in the vascular system. There is the same increase of activity, a heightening of tension. Bruno Wolff, from experiments on bitches, concluded that the central nervous system in women is probably more easily excited in the pregnant than in the non-pregnant state, though he was not prepared to call this cerebral excitability "specific."[[180]] Direct observations on pregnant women have shown, without doubt, a heightened nervous irritability. Reflex action generally is increased. Neumann investigated the knee-jerk in 500 women during pregnancy, labor, and the puerperium, and in a large number found that there was a progressive exaggeration with the advance of pregnancy, little or no change being observed in the early months; sometimes when no change was observed during pregnancy the knee-jerk still increased during labor, reaching its maximum at the moment of the expulsion of the fœtus; the return to the normal condition took place gradually during the puerperium. Tridandani found in pregnant women that though the superficial reflexes, with the exception of the abdominal, were diminished, the deep and tendon reflexes were markedly increased, especially that of the knee, these changes being more marked in primiparæ than in multiparæ, and more pronounced as pregnancy advanced, the normal condition returning with ten days after labor. Electrical excitability was sensibly diminished.[[181]]
One of the first signs of high nervous tension is vomiting. As is well known, this phenomenon commonly appears early in pregnancy, and it is by many considered entirely physiological. Barnes regards it as a kind of safety valve, a regulating function, letting off excessive tension and maintaining equilibrium.[[182]] Vomiting is, however, a convulsion, and is thus the simplest form of a kind of manifestation—to which the heightened nervous tension of pregnancy easily lends itself—that finds its extreme pathological form in eclampsia. In this connection it is of interest to point out that the pregnant woman here manifests in the highest degree a tendency which is marked in women generally, for the female sex, apart altogether from pregnancy, is specially liable to convulsive phenomena.[[183]]
There is some slight difference of opinion among authorities as to the precise nature and causation of the sickness of pregnancy. Barnes, Horrocks and others regard it as physiological; but many consider it pathological; this is, for instance, the opinion of Giles. Graily Hewitt attributed it to flexion of the gravid uterus, Kaltenbach to hysteria, and Zaborsky terms it a neurosis. Whitridge Williams considers that it may be (1) reflex, or (2) neurotic (when it is allied to hysteria and amenable to suggestion), or (3) toxæmic. It really appears to lie on the borderland between healthy and diseased manifestations. It is said to be unknown to farmers and veterinary surgeons. It appears to be little known among savages; it is comparatively infrequent among women of the lower social classes, and, as Giles has found, women who habitually menstruate in a painless and normal manner suffer comparatively little from the sickness of pregnancy.
We owe a valuable study of the sickness of pregnancy to Giles, who analyzed the records of 300 cases. He concluded that about one-third of the pregnant women were free from sickness throughout pregnancy, 45 per cent. were free during the first three months. When sickness occurred it began in 70 per cent. of cases in the first month, and was most frequent during the second month. The duration varied from a few days to all through. Between the ages of 20 and 25 sickness was least frequent, and there was less sickness in the third than in any other pregnancy. (This corresponds with the conclusion of Matthews Duncan that 25 is the most favorable age for pregnancy.) To some extent in agreement with Guéniot, Giles believes that the vomiting of pregnancy is "one form of manifestation of the high nervous irritability of pregnancy." This high nervous tension may overflow into other channels, into the vascular and excretory system, causing eclampsia; into the muscular system, causing chorea, or, expending itself in the brain, give rise to hysteria when mild or insanity when severe. But the vagi form a very ready channel for such overflow, and hence the frequency of sickness in pregnancy. There are thus three main factors in the causation of this phenomenon: (1) An increased nervous irritability; (2) a local source of irritation; (3) a ready efferent channel for nervous energy. (Arthur Giles, "Observations on the Etiology of the Sickness of Pregnancy," Transactions Obstetrical Society of London, vol. xxv, 1894.)
Martin, who regards the phenomenon as normal, points out that when nausea and vomiting are absent or suddenly cease there is often reason to suspect something wrong, especially the death of the embryo. He also remarks that women who suffer from large varicose veins are seldom troubled by the nausea of pregnancy. (J. M. H. Martin, "The Vomiting of Pregnancy," British Medical Journal, December 10, 1904.) These observations may be connected with those of Evans (American Gynæcological and Obstetrical Journal, January, 1900), who attributes primary importance to the undoubtedly active factor of the irritation set up by the uterus, more especially the rhythmic uterine contractions; stimulation of the breasts produces active uterine contractions, and Evans found that examination of the breasts sufficed to bring on a severe attack of vomiting, while on another occasion this was produced by a vaginal examination. Evans believes that the purpose of these contractions is to facilitate the circulation of the blood through the large venous sinuses, the surcharging of the relatively stagnant pools with effete blood producing the irritation which leads to rhythmic contractions.