Etiology. A perfectly satisfactory explanation for the occurrence of placenta prævia has not yet been found. Clinical observation shows that any chronic inflammation or congestion of the womb predisposes to it. Hence placenta prævia is three to six times more common in multiparæ than in primiparæ, and is more often met with in the working classes. Uterine myomata and carcinoma of the cervix are predisposing causes, on account, no doubt, of the endometritis that accompanies them. Ingelby reports two cases of abnormally low situation of the tubal orifices, in one of which placenta prævia occurred three times; in the other, ten. Multiple pregnancies, according to Winckel, furnish four times as many cases of placenta prævia as do single pregnancies, and a woman beginning to bear children late in life is liable to placenta prævia in subsequent pregnancies. Uterine malformations are apparently a predisposing cause. A case is reported by Schwarz of uterus bicornis in which placenta prævia recurred three times. Hofmeier and Kaltenbach1 furnish the best explanation for the abnormal situation of the placenta. These observers have demonstrated, by the examination of young ova, that the chorion villi in the lower pole of the ovum may develop in an hypertrophied decidua reflexa, thus carrying the placenta down to and across the internal os. At first an adhesion between the decidua vera and the reflexa is prevented by catarrhal discharge, but as the ovum develops the reflexa may adhere to the vera, thus fixing the placenta in its abnormal situation, permitting its continued growth, and giving rise to an apparent hypertrophy of the decidua serotina. Gottschalk's observation of a young ovum implanted at the edge of the internal os demonstrates that an abnormally low attachment of the ovum in the uterine cavity may be accountable for placenta prævia. Varieties.-Four divisions are made of cases of placenta prævia -central, partial, marginal, and lateral. In the first the center of the placenta lies over the internal os; in the second the greater mass of the placenta lies upon one side of the lower uterine segment, usually the left (56: 37, Müller), though the internal os is completely covered by it; in the third a margin of the placenta projects over the internal os; in the fourth the placenta is situated upon one side of the lower uterine segment and only the edge of it projects into the cervical canal, if it does so at all, when the os is fully dilated. This classification is justified upon clinical grounds. In central and partial placenta prævia the hemorrhage begins early in pregnancy, is profuse and 1 "Lehrbuch der Geburtshülfe.” 66 2 Verhandl. d. deutsch. Gesellsch. f. Gynäk.," Bd. vii, 1897, S. 289. frequently repeated, and in labor is more dangerous than is the hemorrhage of the lateral variety. There is an added difficulty. too, on account of the obstruction offered by the placenta, stretched across the internal os, to the spontaneous descent of the child, or to the physician's efforts to reach and extract it. In lateral placenta prævia hemorrhage usually does not occur till labor is well advanced, and often does not appear at all. Lateral and marginal placenta prævia are the commonest varieties. In 270 cases the placenta was marginal and lateral 217 times; central and partial 53 times (Winckel). Strictly speaking, central placenta prævia is very rare. There is almost invariably more of the placenta on one side the internal os than on the other. Fig. 427. Varieties of placenta prævia: in A there are seen the normal, lateral, and marginal implantation; in B there are represented the implantation of the placenta at the fundus, which is rare, and implantation over the internal os; in C lateral implantation and that of a cotyledon immediately over the internal os; and in D partial implantation (Dickinson). Clinical History.-A woman with placenta prævia may begin to bleed as early in pregnancy as the second month, but the first hemorrhage usually occurs in the last trimester. There is a sudden gush of blood, often without apparent cause and without pain. The bleeding commonly recurs in increasing amounts and at decreasing intervals as pregnancy advances. In very rare cases the blood leaks away continuously (stillicidium), though this is more characteristic of the premature separation of a normally situated placenta. The cause of the hemorrhage during pregnancy is the impact of the embryo and fetus upon the placenta, the pressure of the ovum upon the lower uterine segment, and the imperfect attachment of the placenta in certain areas to the uterine wall. A prediction of the amount of bleeding in labor can not always be made by the amount of blood lost or the frequency of the hemorrhages in pregnancy. The first hemorrhage may occur in labor, which may be ushered in by a tremendous outpour of blood, even in lateral placenta prævia. Ordinarily, however, the greater the bleeding during pregnancy, the more likelihood is there of serious hemorrhage in labor. The bleeding in labor is easily explained. The placenta is attached in that portion of the uterine cavity which must be dilated to allow the advance of the presenting part. The stretching of the uterine walls expands the area of the placental site, and necessarily detaches the placenta, while the reversal of the ordinary mechanism of placental detachment keeps the gaping mouths of the torn uteroplacental vessels wide open, and allows the blood to pour from them till the hemorrhage is checked by syncope, by thrombosis, by the pressure of the presenting part, or by a vaginal tampon. The source of the bleeding in rare cases is a rupture of the circular sinus of the placenta, a laceration of the fetal vessels or of the cervix. The bleeding is usually most profuse just as the uterine contraction passes off. During the height of the pains it may cease altogether, from the pressure of the presenting part or of the intra-uterine contents upon the placental site. As the placenta occupies a portion of the space in the lower uterine segment and may prevent the descent of the presenting part, abnormalities in the presentation and position of the fetus are common. Transverse and oblique positions are ten times, breech presentations four times, more frequent than in normal labor. In the first stage of labor, inertia uteri is common, partly because the cervix is not pressed upon and reflex irritation is absent, partly on account of the loss of blood. The os is usually patulous, even before labor begins, and the cervical canal is easily dilated. Occasionally, however (twelve per cent.), the os is contracted and the cervix rigid. The insertion of the cord is often marginal or velamentous, and prolapse of the cord is common. The placenta is often anomalous in shape, size, thickness, and weight. There is frequently a placenta succenturiata. As the os dilates the placenta may be torn and thus separated into two parts. An adherent placenta may be expected in more than a third of the cases (Müller, thirty-nine per cent.). After labor there is a tendency to inertia, and consequently to postpartum hemorrhage, and there is an extraordinary liability to septic infection. Placenta prævia, as a complication in labor, would be much more common than it is if it did not so often interrupt pregnancy. The frequency of abortion and miscarriage is placed in different statistics at forty to sixty per cent. In quite a large proportion of cases placenta prævia would be unrecognized in labor without a careful examination of the membranes and placenta afterward. Even in the marginal variety the presenting part, unobstructed, may descend quickly, exerting such pressure upon the placental site that bleeding does not occur. Symptoms and Diagnosis.-Repeated hemorrhages during the latter part of pregnancy make the diagnosis of placenta prævia almost certain. On digital examination the cervix is found enlarged in all directions; the vaginal vault is soft and boggy the presenting part can not be plainly felt; pulsating vessels are detected around the cervix; the external os is dilated and the cervical canal is patulous to the internal os, through which a finger can easily be pushed. Under favorable conditions the placenta may be felt through the abdominal walls, as was first pointed out by Spencer. Finally the maternal face of the placenta or its margin is felt over the internal os, the uneven surface of the cotyledons and a gritty feel distinguishing it from a blood-clot, the membranes, or the presenting part. During the first stage of labor the causes of hemorrhage are lacerations of the birth-canal, rupture of blood-vessels, and placenta prævia. The hemorrhage of placenta prævia occurs early, with unruptured membranes, with feeble pains or in their absence altogether, and the symptoms of uterine rupture and of lacerations along the lower birth-canal are absent. In the rare event of a ruptured blood-vessel along the lower birth-canal, the blood does not flow from the uterine cavity. Treatment. If a placenta prævia is detected during pregnancy, gestation should be terminated at the end of the seventh month, or at any time thereafter that the diagnosis is established. The hemorrhage before the thirty-second week is scarcely ever dangerous, though in one case I was obliged to induce abortion before the fifth month on account of a loss of blood that was almost incessant. After the seventh month the In the 128 deaths of Müller's statistics there was not one before the seventh month. |