DURATION OF PREGNANCY. 939 



The changes in the walls of the uterus during pregnancy are very important. The 

 blood-vessels become much enlarged, and the muscular fibres increase immensely in size, 

 so that their contractions are very powerful when the foetus is expelled. 



It is evident that, on account of the progressive increase in the size of the uterus dur- 

 ing pregnancy, it cannot remain in the cavity of the pelvis at the later months. During 

 the first three months, however, when it is not too large for the pelvis, it sinks back into 

 the hollow of the sacrum, the fundus being directed somewhat backward, with the neck 

 presenting downward, forward, and a little to the left. After this time, however, the 

 increased size of the organ causes it to extend into the abdominal cavity, so that its 

 fundus eventually reaches the epigastric region. Its axis then has the general direction 

 of the axis of the superior strait of the pelvis. 



The enlargement of the uterus and the necessity of carrying on a greatly-increased 

 circulation in its walls during pregnancy are attended with a temporary hypertrophy of 

 the heart. According to Robin, it is mainly the left ventricle which is thickened during 

 utero-gestation, and the increase in the weight of the heart at full term amounts to more 

 than one-fifth. After delivery, the weight of the heart soon returns to nearly the nor- 

 mal standard. 



Duration of Pregnancy. The duration of pregnancy, dating from a fruitful inter- 

 course, must be considered as variable, within certain limits. The method of calculation 

 most in use by obstetricians is, to date from the end of the last menstrual period. Dr. 

 Matthews Duncan, who has made quite a number of observations upon this point, states 

 that the 278th day after the end of the last menses is the average day of delivery ; but 

 he admits that his method of calculation is rough, though he cannot find any that is more 

 reliable. The observations upon which this opinion is based are the following : The day 

 was predicted in 153 cases; in 10 cases, confinement occurred on the exact day; in 80 

 cases, the confinement occurred sooner, presenting an average of 7 days for each case ; 

 and, in 63 cases, the confinement occurred later, presenting an average of 8 days for each 

 case. The great difficulty in predicting the exact time of confinement, which is very 

 important in practice, is mainly due to the comparatively small number of reliable obser- 

 vations in which the pregnancy can be dated from a single intercourse or from intercourse 

 occurring within two or three days. We have received from Prof. Fordyce Barker the 

 following very interesting account of a case in which this observation was made in his 

 own practice : A lady, concerning whose statements there could be no suspicion of inac- 

 curacy, residing in New York, received a visit from her husband, after along interval of 

 absence. He arrived in this city from New Orleans, remained thirty-six hours, and then 

 went to Europe, where he remained for four months. Exactly 298 days from the date of 

 the first visit of the husband, the lady was confined and delivered by Prof. Barker. This 

 occurred in 1852. Taking into account the various cases which are quoted by authors, 

 in which conception has been supposed to follow a single coitus, there appears to be a 

 range of variation in the duration of pregnancy of no less than 40 days, the extremes 

 being 260 and 300 days. 



In the very interesting observations of Kundrat and Engelmann, upon the changes of 

 the uterine mucous membrane during menstruation, published in 1873, the idea is ad- 

 vanced that pregnancy dates really from a menstrual period which is prevented, as far as 

 a discharge of blood is concerned, by fecundation of an ovum, and not from the period 

 immediately preceding, in which the flow takes place. This theory was proposed by 

 Loewenhardt, in 1872. If we adopt this view, the changes in the mucous membrane of 

 the uterus ordinarily terminate in a fatty degeneration of the vascular walls, which re- 

 sults in a capillary hemorrhage ; if, however, an ovum be fecundated, these changes do 

 not pass into fatty degeneration, but advance to an hypertrophy, which is the first stage 

 in the formation of the decidua. The arguments in opposition to this method of calcu- 

 lating the duration of pregnancy are the following: The time, with relation to the men- 



