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=Effect of Parity in Women on the Pattern of Uterine Enlargement during the Latter Half of Gestation=

S. R. M. Reynolds And J. Tyler Baker

Dcpmtment of Eméryology, Carnegie Im‘titm'iorz of Washington, and Mc>m0rial Hospital, Easton, Maryland

With eleven text ﬁgures 

==Introduction==

One of the important features of uterine accommodation of the products of conception is that the uterus undergoes a characteristic pattern of enlargement during the course of gestation (Reynolds, 1946). These changes in shape have been stressed in a number of studies in which important correlations were made between the shape of the conceptus at any time in pregnancy and the How of maternal blood through the uterus on the one hand (Reynolds, 1947), and fetal maturity and welfare on the other (Reynolds, 1949). Though the basic studies in this work have been made on the rabbit, they have been extended in one way or another to the hamster, rat, guinea pig (Bradin, 1949), monkey (Gillespie, Ramsey, and Reynolds, 1949), and man (Gillespie, 1950).


In the studies on primates just cited, observations on the shape of the uterus during pregnancy were made by analysis of X-ray pictures of the ventral and lateral aspects of the uterus. In monkeys, the uterus was found to increase in size, more or less proportionately, in all three dimensions until about the 100th day of gestation. Between that day and the 105th day the pattern of enlargement undergoes a marked alteration. Growth becomes predominantly longitudinal in direction, although the uterus does, of course, become somewhat wider as pregnancy advances.


In 12 women, similar studies were made without regard to previous pregnancies. Study of X rays of these women showed two periods of change in the pattern of uterine enlargement. Between the 20th and 22d weeks, the uterus ceases to enlarge as a spheroid (i.e., in three dimensions), and begins, instead, to elongate while continuing to grow wider. Between the 28th and 30th weeks, the uterus undergoes a temporary phase of slower lateral widening.

==Pattern of Uterine Enlargement and Functional Conditions==

The signiﬁcance of these changes, especially the conversion from a pattern of spheroidal to elongating enlargement, is referable to two types of phenomena. First and most important, the period of conversion signifies that the fetus has entered upon its period of rapid enlargement and maturation. Second, uterine conversion is associated with a transitory uterine ischemia resulting from local hydrostatic forces within the uterine tissues. These forces are largely determined by the shape of the uterus at that time as determined by the ratio of the size of the uterus to that of the fetus and its associated structures.


The basic facts concerning uterine accommodation during pregnancy were summarized by Reynolds (1949), with particular reference to conditions obtaining in the rabbit. The observations made upon the uterus of the primate have hitherto been confined, as stated, to X-ray studies. These rested upon a total of about 70 observations made on 6 monkeys, and about 150 similar observations on 15 pregnant women. Some of these women were multiparous, some nulliparous. Not all the pregnancies were entirely normal. Even so, the cardinal pattern of uterine enlargement during the latter half of pregnancy in women is established.


The present study was made for three purposes: ﬁrst, to extend our present knowledge by additional data obtained independently; second, to accomplish this by means of direct caliper measurement of uterine dimensions in patients; third, to obtain data on a suﬂiciently large group of subjects to permit separate evaluation of the pattern of uterine enlargement dur— ing pregnancy in primigravid and in multigravid subjects. It was believed that thus a basis for some of the well known but as yet not understood differences between primi— and multigravidae with respect to the complications of late pregnancy might be indicated. Differences in the pattern of uterine enlargement were found, as recorded below, although it is clear that the main problem of what these differences signify in functional terms must be established by future research. 


==Material and Methods==

In 1948, one of us (S. R. M. R.) presented to a group of conferees in the Department of Obstetrics in Iohns Hopkins Hospital the results of his studies on uterine accommodation in the rabbit. The other (I. T. B), having attended that conference, began incorporating into his regular ollice examinations of prenatal patients in Easton, Maryland, observations on the height and width of the uterus. Biweekly records were obtained from the earliest time at which the height and width of the uterus could be measured.


The measurements were made as follows: By the use of calipers, the lateral dimension of the uterus was measured in centimeters at the points of maximum palpable width. The height of the uterus was estimated by measuring the distance in centimeters from the inferior margin of the symphysis pubis to the highest palpable point of the fundus. Since the anterior lip of the cervix lies at about the level of the symphysis pubis (Ivy, 1942), this measurement approaches the actual length of the uterus. For each measurement, the patient lay relaxed and supine.


There are several possible causes of error in such methods of measurement. The width and height measurements will vary, no doubt, depending upon the position of the fetus, the amount of adipose tissue in and on the abdomen, and the amount and location of abdominal contents, including gas within the intestines. Finally, no attempt was made to rule out the effect of Braxton—Hicks contractions at the time of measurement. As a result, it would be expected that the data obtained would show considerable scatter, and that the progress of uterine enlargement in any one subject would not be determinable. This was found to be the case. Attempts to plot the data for individual cases showed considerable fluctuations, so much so that it is not possible to deduce any facts concerning uterine enlargement from speciﬁc, individual instances in this series of cases. Nevertheless, the data taken as a whole may be regarded as grouped data to be viewed in a statistical sense, in order that average conditions pertaining to height and width of the uterus may be understood. Thus, in spite of the fact that these data represent a complex set of measurements which are inﬂuenced by a number of extraneous and undetermined and in part indeterminable factors, they are highly instructive in showing what the pattern of uterine enlargement in the latter half of pregnancy tends to be, on the average, in two groups of women, one primigravidae, the other multigravidae.


The cases selected for study comprised 24 women in their first pregnancies and 30 in second or later pregnancies. Only completely normal cases are included. All were normal with respect to the course of gestation and the onset and progress of labor. All were delivered between the 38th and 41st weeks of pregnancy. No cases of multiple births are included. All the women were white private patients from a relatively small rural community. VVe have, therefore, two clinically homogeneous groups of women for study.


Data will be presented for these two groups of patients with respect to (:1) the height of the fundus above the symphysis pubis; ([2) the maximum width of the uterus; (c) the height :width ratio of the uterus, which expresses the degree of lengthening of the uterus when this ratio exceeds 1.00.

In multigravidae, some uteri were suﬂiciently palpable for measurement by the 12th or 14th week of pregnancy. In primigravidae, no uteri were sulﬁciently palpable externally for these measurements to be made until the 14th week of gestation. After these stages, measurements could be made in all patients, and were so made as opportunity permitted until the 40th week of pregnancy.

==Results==

===Height of the Fudus===

Primigrrwidae. The height of the fundus above the symphysis pubis in primigravidae was variable, as might be expected for the reasons given above. The range of measurements made at any one stage of gestation was, however, only about 6 to 10 cm. By inspec tion of the distribution of the data in ﬁgure 1, the mean curve could be drawn in the graph without difficulty, as shown by the heavy black line.

The curve in primigravidae shows that, starting at about 16 cm. at the 20th week of pregnancy, the fundus height increases rapidly but at a slightly 

CENTIMETERS


HEIGHT OF’ THE FUNDUS

34 ABOVE THE SYMPHYSIS PUBIS PRIMIGRAVIDAE . . 32 O O .0 OD . . 0:5 000 30 )_o.

28

26

24

22


N O

5

I4 20 22 24 26 WEEKS OF PREGNANCY



28 30 32 34 36 38 40

FIG. I. Height of the fundus uteri above the level of the S}’[1‘lpi'1}-‘Sis pubis as nieasiircd by calipers in :4 primigrzivid subjects at different times during pregnancy. Curve placed by inspection.

HEIGHT OF THE FUNOUS

22

20

55

CENT|M_ETERS O5


20 22 24 26 WEEKS OF PREGNANCY

34 ABOVE THE SYMPHYSIS PUBIS MULTIGRAVIDAE o o 00 32 o 00 0:0 0 0 o: 0 0 co 0 0: co: .°.° “‘ no 0 0 .:s_,o::#.o: 3° . ' ' °:"="-"1'==='::':: 0 oo o o 00 00°”. 0 9 O . .009 0 CO0 C 23 oo a too on can 0 no 0 . - C ‘II : 0:: I :.9OX U 2 FIG. 2. Height of the fundus uteri above the 4' " ° ' °° ° ' level of the syn1pl1ysis pubis as measured by 26 /2 " '° 2' _ ° ° ° ° calipers in 30 imiltigmvid subjects at different o o o o «co -o-an-mono-o-o o times during pregnancy. Curve placed by 24 inspection.


28 30 32 34 36 38 40 80 PARITY AND UTERINE ENLARGEMENT

diminishing rate until about the last 2 weeks of pregnancy, when it nears its asymptote at a height of about 31 cm. above the symphysis pubis.

Multigravz'dae. The distribution of data from the group of multigravid subjects (fig. 2) showed marked variation, rather more than in primigravidae, prior to the 28th week of gestation. As in primigravidae, the

3, HEIGHT or-' THE FUNDUS DURING PREGNANCY

- MULTIGRAVIDAE ,6 30 o PRIMIGRAVIDAE °

29

28

26

25 24

23

22

2|



N! O

6

ET:

CENTIMETERS _ C5

5

20 22 WEEKS OF PREGNANCY

24 26 28 30 32 34 36 38 40

Fin. 3. Comparison of average curves of fundal heights in primi- and multigravid subjects. Based on mean curves of ﬁgures I and 2.

increase in height of the fundus continues toward an asymptote of about 31 cm. In contrast with the situation in primigravid subjects, however, the increase continues at a slightly more regular rate but with smaller increments in the last 2 weeks of pregnancy. I”rin2:'g2'az/iduc ucwrrs nzzzltigrauirlrze. Figure 3 shows that there is little apparent difference between the average curves for the height of the fundus during the last 20 weeks of pregnancy. The slight difference that appears in Figures I and 2 for the 20th to 26th weeks shows in figure 3, where the data for primigravidae (circles) occupy a lower position than the comparable data (clots) for the multigravidae. Then, from the 26th to the 39th week, the height of the fundus in primigravidae is greater than it is in multigravidae (except for the 31st and 32d weeks, when they are equal). Only in the last 2 weeks of pregnancy is the situation reversed. This comparison suggests that during the period spanning the 26th to the 36th week of pregnancy, the uterus of the primigravidae encounters less resistance to lengthening than it does to lateral and dorsoventral enlargement. The multigravid uterus, however, is less restrained by lateral or dorsoventral resistance to enlargement. As a result, it rises a little less rapidly toward its ultimate height.


COMPARISON BY GRAVIDITY OF WEEKLY REGRESSION IN HEIGHT OF THE FUNDUS





4: Ln ’c:mbo‘<o'5

0 MULTIGRAVIDAE o PRIMIGRAVIDAE

HEIGHT OF THE FUNDUS _REGRESS|ON to

.I I8 20 22 24 28 32 36 40

WEEKS OF PREGNANCY

FIG. 4. Differences in pattern of increase in height of fundus uteri in primi— and multigravid subjects respectively, as shown by regression curves.


The difference between the primigravid and the multigravid uterus is shown more clearly in the regression curves of ﬁgure 4. Regression curves indicate that proportion of the total distance to be traversed along the ordinate which is gained in any unit period of time (along the abscissa). For example, the primigravid uterus attains some 50 per cent of its total increase in height between the 20th week and the 28th week. The multigravid uterus consistently gains somewhat less than this. Thus we see that throughout the latter half of pregnancy in primigravid women the average weekly regression in height of the fundus above the symphysis pubis exceeds that of the multigravid uterus. Clearly, therefore, comparison of these curves shows that the the curve approaches an asymptote near the end of pregnancy.


Mzzltigrcwidae. In figure 6, the same general relationship is seen to hold for multigravidae. To the eye, there appears to be but a slight difference between the two curves, except that in multigravidae the increment in width is slightly greater, and the asymptote approached at term is just under 24 cm., or some 2 cm. greater, on the average, than is the case in primigravidae.

I’rz'n2igmm'dae versus rrzzzltigraz/idae. The contrast

WIDTH OF THE UTERUS


26 MAXIMUM PRIMIGRAVIDAE . . O. 24 - - ° ° . oo 0 o 0 O O I IO 9 CC DOC 0 0 C00 .0: COD 0 00?? 22 o I . . :. 034:»: "33 00 o . .’’¢/o:’.‘. 0000 0.0: 00 00 O K O . " 0:: o°:°¢{o(.:.: 0°; :0 o no on uo°o.o0°00 r M ' ‘ll fh 20 - ' ° ' ' rm. 5. . - aximum W1( t 1 o t e uterus, measured by calipers, in primigravid o . 0 . . . subjects. Curve placed by inspection. I8 ° ° C | O O O 0 I4

to

a:

ll

u.I|2

3

I 2

“lo

°2o 22 24 26 23 so 32 34 35 33 40

WEEKS OF PREGNANCY

physical forces, which are hydrostatic in nature (Reynolds, 1946), tend to produce greater elongation in primigravidae than in multigravidae.

WIDTH or THE UTERUS

Complementing the foregoing discussion, the data shown in ﬁgures 5, 6, 7, and 8 show the other side of the story just outlined, namely, that the curve of maximum average width of the uterus during the latter half of gestation differs in multigravid and primigravid subjects.

Pn'nzz’gr:zw'c1rze. In this group (see fig. 5) the width of the uterus increases from just under 16 to a little over 22 cm. during the latter half of pregnancy. The increment is at a slightly diminishing rate, so that between the patterns of widening of the uterus in the two groups of subjects is shown especially well in ﬁgure 7. It is clear that the multigravid uterus increases more rapidly, especially from the 30th week of pregnancy on, than does the primigravid uterus. Thus we see that the resistance to increase in the lateral dimension of the uterus is less in the multigravid than in the primigravid uterus. This accords well with, and confirms, the conclusion stated above with respect to the factors contributing to the pattern of increase in height of the fundus.


The regression curves for the lateral enlargement of the uterus in both groups of patients are shown in ﬁgure 8. They reveal instantly that the nature of lateral enlargement of the uterus is more complex traversed along the ordinate which is gained in any unit period of time (along the abscissa). For example, the primigravid uterus attains some 50 per cent of its total increase in height between the 20th week and the 28th week. The multigravid uterus consistently gains somewhat less than this. Thus we see that throughout the latter half of pregnancy in primigravid women the average weekly regression in height of the fundus above the symphysis pubis exceeds that of the multigravid uterus. Clearly, therefore, comparison of these curves shows that the the curve approaches an asymptote near the end of pregnancy.


Multz'graw'dac. In ﬁgure 6, the same general relationship is seen to hold for multigravidae. To the eye, there appears to be but a slight difference between the two curves, except that in multigravidae the increment in width is slightly greater, and the asymptote approached at term is just under 24 cm., or some 2 cm. greater, on the average, than is the case in primigravidae.

I’rr'nzz'gram'dac versus multigraz/idae. The contrast

WIDTH OF THE UTERUS

26 MAXIMUM PRIMIGRAVIDAE . . I. 24 ' ° 9 O0 0 O O 00 9 00 000 CC. .. CC. 00 :o°d"5j 22 0 00 .’:::: 9' out 000 °° to C IO . 2° C.‘ .0. .0 ..Q.“... FIG. 5. Maximum width of the uterus, ° . ° ,

measured by calipers, in primigravid subjects. Curve placed by inspection. I8

I4

F5

OENTIMETERS

I0


20 2 2 24


26 28 30 32 34 36 38 40

WEEKS OF PREGNANCY

physical forces, which are hydrostatic in nature (Reynolds, 1946), tend to produce greater elongation in primigravidae than in multigravidae.

VVIDTH or THE UTERUS

Complementing the foregoing discussion, the data shown in ﬁgures 5, 6, 7, and 8 show the other side of the story just outlined, namely, that the curve of maximum average width of the uterus during the latter half of gestation differs in multigravid and primigravid subjects.

Pr:'mz'gr:zw'dae. In this group (see ﬁg. 5) the width of the uterus increases from just under 16 to a little over 22 cm. during the latter half of pregnancy. The increment is at a slightly diminishing rate, so that

between the patterns of widening of the uterus in the two groups of subjects is shown especially well in figure 7. It is clear that the multigravid uterus increases more rapidly, especially from the 30th week of pregnancy on, than does the primigravid uterus. Thus we see that the resistance to increase in the lateral dimension of the uterus is less in the multigravid than in the primigravid uterus. This accords well with, and conﬁrms, the conclusion stated above with respect to the factors contributing to the pattern of increase in height of the fundus.

The regression curves for the lateral enlargement of the uterus in both groups of patients are shown in ﬁgure 8. They reveal instantly that the nature of lateral enlargement of the uterus is more complex 



WIDTH OF THE UTERUS

25 MAXIMUM . MULTIGRAVIDAE 00 0 00 ... 0 .. 0 24 0 . 00 0 000 0 0.0% :: ‘:2; :0 o 000 g 0 00 :° 0:0 .0.0‘_g00":::.::—:: 0 u 000000 000 00 000 00 22 o 0 o 000 00 9:0 3:. :.Z :0: o 900 0 ° 0 9° °yo;o 9'9’. 00 :0 0:: 0'0°0 :: 0000: ° '5 000 00 O 2 0 000 0:0 Jo o:o00.0"0':0::: 00: no 9 : 9 9 0 00 "if. : 0 : g 0/0 :. |8 0 on o 3 .9 g g 1:. . ° ,_ :. ° 0 I6 ° co 0 CO . 0

MI4 °

C

I.lJ

5:2

E

I 2

8:0


20 _ 22 24 26 28 30 32 34 36 38 40

WEEKS OF PREGNANCY

Fro. 6. Mzucimum width of the uterus, measured by calipers, in multigravid subjects. Curve placed by inspection.

COMPARISON OF WIDTH OF UTERUS IN PRIMIGRAVIDAE AND MULTIGRAVIDAE 24

' MULTIGRAVIDAE ° PRIMIGRAVIDAE



22

2|

20

CENTIMETERS an

I5




20 22 24 26 28 30 32 34 36 38 40 WEEKS OF PREGNANCY

FIG. 7. Comparison of the pattern of increase in width of the uterus in primiand multigrzwid subjects. Based upon the curves of ﬁgures 5 and 6. PARITY AND UTERINE ENLARGEMENT 83

than is the pattern of elongation of the uterus. In primigravidae, the weekly regression at ﬁrst is about equal to that in multigravidae. After the 28th week a divergence in regression occurs: the proportion of the remaining gain in width to be achieved increases more and more rapidly in multigravid than it does in primigravid women. The absolute increase in width at this time in multigravidae is really very slight, however, despite the fact that the regression rate is greater.

COMPARISON OF WEEKLY REGRESSION




I38 IN WIDTH on-' THE UTERUS

$38 6'0 °“o\o

' \s,_\

5.0 x\

4.0 °\\:

3.0 ‘ ’

\\ 2.0 \\ \ \ "3 Eng 3 is \ ‘mg .7 3 .6 u: -5 I .4 0'! D 3 E - OMULTIGRAVIDAE '5 o PRIMIGRAVIDAE. \ .2 °

LI. 0 E 9 I 3 ‘is 20 24 23 32 36 40

WEEKS OF PREGNANCY

Frc. 8. Comparison of weekly regression in widening of the uterus in primi- and multigravid subjects respectively. Observe that after the 28th week the rate of regression is much faster in multigravidae than it is in primigravidae.

INDEX or ELONGATION or THE Uranus

In order to evaluate the pattern of uterine enlargement, an index of uterine elongation was calculated for each set of measurements for each patient by dividing the observed length by the observed width. Gillespie (1950) has observed that until about the 20th week of pregnancy the pattern of uterine enlargement is spheroidal. For this reason, the curve of elongation is drawn as a straight line at a ratio of 1.0, or slightly over, in ﬁgures 9 and 10.

Prz'mt'grrwidac. After the 21st week of gestation, when uterine conversion occurs, the average curve for the elongation index rises abruptly but at a rapidly diminishing rate (ﬁg. 9). It approaches an asymptote of 1.45. That is to say, at the end of pregnancy in primigravidae, the length exceeds the width by 45 per cent. The amount of scattering of the individual points of these data is greater than in the preceding graphs. This may be attributed to the fact that each point represents the relation between two measurements, each of which in turn is subject to considerable error for the reasons outlined under “Methods and results," above.

Mzrltigrazzidae. The curve shown in ﬁgure 10 for average elongation in multigravid women is rather similar to that of ﬁgure 9, for the primigravidae. It difiers in two important respects, however. First, the process of elongation (i.e., uterine conversion) commences in the 18th week of pregnancy rather than in the 21st week as in primigravidae. Second, the asymptote approached in multigravidae is 1.36. That is, the length of the uterus at term exceeds the width by 36 per cent, in contrast with 45 per cent in primigravidae. Again we see, therefore, that in multigravidae the resistance to widening is less than it is in primigravidae.

Regression of uterine elongation. Figure II gives the regression curves for the primigravid and multigravid uteri shown in ﬁgures 9 and 10. The curves show several interesting features. First, the regression is represented, for all practical purposes, by a straight line in each case, after conversion of the pattern of uterine enlargement from a spheroidal to an elongating one. These lines are projections from an ideal point for each curve which lies in the 13th week of pregnancy (see ﬁg. 11). At the time of conversion, therefore, a diFference already exists between primiand multigravidae in the pattern of uterine enlargement.

Another interesting feature of these curves is that the multigravid elongation index regresses at a more rapid rate than does that of the primigravidae. The absolute amount of elongation is less, it will be remembered. Only the proportion of the remaining elongationzwidth ratio attained each week is greater in multigravidae than in primigravidae. VVC see, therefore, that weekly progress in attainment of ultimate elongation is slower in primigravidae than in 84 PARITY AND UTERINE ENLARGEMENT

FUNDUS HEIGHT TO UTERINE WIDTH INDEX (ELONGATION INDEX) DURING PREGNANCY PRIMIGRAVIDAE '’ ° °

INDEX_ on in O O

on C0 0 0.0 o 0 O o no on °°° no 3 oo

o no ° 9 o o 0 0 I '° o E 3 0 0° 0 O C 013.3% 0 o 0 ° :¢Il"’°.'§.‘.o§.. gag ‘lo. 0 o o 0 3 :—'oo on 5 :0: 308 . o 2/: I °° o °3"

/W'°T__lf u TE_RUS 8

,, °3§.‘-:'8
FuNDus_ - I\) O O I’ 9 I I Cl. 0 I '9' o l.

I‘ ° 0 o 9 E I.oD ° °° , “J o I C 0 0.90 0.80 ° I 000'"


l2 l4 I6 I8 20 22 24 26 28 30 32 34 36 38 40 WEEKS OF PREGNANCY

FIG. 9. Pattern of elongation of the uterus in primigravidac, based upon calculation of the lieiglitzwidth ratios at diflerent times in pregnancy. Until the 21st week enlargement is considered to be about equal in each dimension, as indicated by the horizontal straight line. Conversion to a pattern of elongation is indicated by the deviation from the horizontal after that time.

FUNDUS HEIGHT TO UTERINE WIDTH INDEX

‘-5 (ELONGATION INDEX) DURING PREGNANCY MULTIGRAVIDAE L5 0 ° ° 0 U °0 0 ° 9 Q 0 ° 0 0 0.0 $0 00 '4 ~ - -- = °°° : ~  : I..~:~_a .I._: 3 ‘O. Oio .6. ’ 0:13» oo 00 I-3 2:’ ~- -s~ is : M} 2-5: 3.2.. ° ‘tr ‘ °5~3~.§. t2 ....:~.°:°°*,,, ° 8 O O


5

to

I |NDEX HEIGHT FUNDUS / W DTH UTERUS ho .

I L-

I2 I4 I6 18 20 22 24 26 28 30 32 34 36 38 40 WEEKS OF PREGNANCY

FIG. 10. Pattern of uterine elongation in multigravidae, based upon calculation of the lieiglttnvidtlt ratios at dillerent times in pregnancy. Conversion from :1 pattern of uniform heiglitzwidtlt increase to one of elongation occurs during the 19th week.

multigravidae. This is because in the former the ultimate elongation, relative to width, to be attained is greater than it is in the latter.

From the 27th to the 29th week of gestation, an interesting and contrasting trend occurs in the regression lines for the two curves. In primigravidae, there is a deviation from a straight regression line in the direction of a transient increase in the regression rate. The opposite effect is seen in the line for multigravid uteri. Since changes in the pattern of enlargement are associated with hydrostatic conditions in the

on straight lines. The curve for each is expressed by the equation

ﬂ1’b117

K—y=Io

(I)

where K is the estimated upper asymptote. For primigravidae this becomes

10g(I-4s—y)=a1—lnx <2)

and for multigravidae 1og<r.36-y>=a2—b2r <3)

The striking regularity of these curves lends credi EFFECT OF GRAVIDITY ON REGRESSION OF THE PATTERN(SHAPEl OF UTERINE ENLARGEMENT DURING PREGNANCY

'-gg \\ . PRIMIGRAVIDAE -L0G(I.45-y)=O'b x

30 \ . MULTIGRAVIDAE..LOG(|.36-y)=o'bx
.70 ‘

E8 SPHEROID go . ENLARGEMENT

PROPORTION OF HF/WU INDEX TO GO TILL TERM

I2 i6 20 WEEKS OF PREGNANCY

24

Z O I<I (D Z O _J LU

28 32 36 40

FIG. 11’. Comparison of regression curves in patterns of uterine elongation. From the first moment of conversion from a pattern of spheroidal to elongating uterine enlargement, a difference in the two curves is evident; they emerge from an ideal

point lying in the 13th week of pregnancy. The regression lines are straight except for transient deviations in opposite directions at about the 28th and 29th weeks in each curve. See text for discussion.

uterus which affect the course of blood flow through

the uterus (Reynolds, 1949), it is possible that this difference between primi— and multigravidae at the

beginning of the third trimester of pregnancy is associated with the higher incidence of complications of pregnancy in primigravidae at this time than in multigravidae.

A ﬁnal interesting point in connection with these regression lines is that in each the points fall so nearly

bility to the View that the average curves for the basic data shown in ﬁgures I, 2, 5, 6, 9, and 10, which were drawn by inspection from widely scattered points, are correctly placed. This being so, the signiﬁcance of the differences noted between the patterns of uterine enlargement in primigravidae and multigravidae is real, and physiological and clinical considerations of gestational mechanisms should take these differences into account. 86 PARITY AND UTERINE ENLARGEMEl\'T

==Summary==

1. Two groups of normal gravid women were available for study. Twenty-four were in their first pregnancy, 30 were in second or later pregnancies. All were single pregnancies.

2. The pattern of uterine enlargement was established by measurement externally, with calipers, of two uterine dimensions, at prenatal oflice visits from the 12th to 14th week of pregnancy onward. The lateral dimension was measured at the points of maximum palpable width. Lengths were measured from the inferior margin of the symphysis pubis to the highest palpable point of the fundus.

3. On the average, the fundus reaches the same height in primi- and multigravid women. In primigravidae the uterus attains its ultimate height at a slightly but deﬁnitely faster rate than in multigravidae.

4. On the average, the multigravid uterus is wider at term than is the primigravid, but the latter approaches its ultimate width at a faster weekly regression rate than does the former.

5. The uterus of the primigravid woman elongates more readily than it widens, in contrast with that of the multigravid woman.

6. The pattern of elongation was judged by dividing the length of the uterus by the width. The uterus enlarges proportionately in three dimensions until elongation begins. In multigravidae, this is in the 18th week of pregnancy; in primigravidae, in the 21st week.

7. At term, in the primigravid uterus the length exceeds the width by 45 per cent; in the multigravid uterus, by 36 per cent.

8. The regression pattern of elongation of the uterus may be expressed by the following equation:

log(K —y) = :7, —Z2,.r

where K is the estimated upper asymptote of the coefficient of elongation.

Regression of uterine elongation in primigravidae and multigravidae takes place at different rates. It is faster in the latter than in the former.

9. From about the 27th to the 29th week of gestation, a temporary trend away from the normal regression curve takes place. This reflects the fact that the primigravid uterus is forced by the growing fetus to elongate more at this time than the multigravid uterus.

==Literature Cited==

Bn.s.n1.\', L. T. 1949. Appearance of ossiﬁcation centers in relation to fetal growth and uterine environment. Anat. Rec., vol. 103, p. 429.

GILLSEPIE, C. 1950. Principles in uterine growth during pregnancy. Amer. Iour. Obstet. and Gynecol., vol. 59, I’P- 949”959 

E. M. RAMSEY, and S. R. M. Rrxmoens. I949. The pattern of uterine growth during pregnancy in monkeys as shown in an X-ray study. Amer. Iour. Obstet. and Gynecol., vol. 58, pp. 758-764.

IVY, A. C. 1942. The functional anatomy of labor, with special reference to the human being. Amer. Jour. Obstet. and Gynecol., vol. 44, pp. 952-972.

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