Pelvic shape of contemporary young women: Related factors ...

1) Faculty of Nursing, Hiroshima International University

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広島国際大学看護学ジャーナル第11巻第１号 2013

Original Article

Pelvic shape of contemporary young women: Related factors and impact on daily life

Haruko Shinkawa1), Yoko Takahata1)

Abstract　Being safe and simple, external pelvimetry is also known for its usefulness in current developments in medical technologies. However, its standard measurement values have been used for more than 40 years, since the 1970s. This study therefore aimed to provide for a better understanding of changes in its standard measurement values by external pelvimetry and how pelvic shape is related to genetic factors, dieting for weight loss, and exercise experience. In addition, this study aimed to elucidate the relationship between pelvic size and balance, the daily discomforts frequently reported by women in early maturity, and to provide data leading to improved care that can contribute to a higher quality of life among women. Our results showed that contemporary women in early maturity have significant development in the intertrochanteric diameter of the pelvis, but no major change in other diameter lines. Development of the intertrochanteric diameter was associated with a higher intertrochanteric diameter-to-external conjugate ratio, but overall, no significant change was noted in pelvic balance. Pelvic size and balance were only slightly influenced by physique at birth and genetic factors, however current body fat percentage was of significant relevance. Of women with discomfort in daily life, those who had leg swelling, stiff neck, urinary incontinence, or abdominal bloating had larger pelvises, especially in the transverse direction, than women who did not have these symptoms. These findings revealed that in women with pelvic pain and fatigability, only the external conjugate is enlarged.

Key words： Discomforts, External pelvimetry, Pelvic balance, Pelvic size, Young women

原　著

現代の成熟期早期の女性の骨盤の形状と

その関連因子，日常生活への影響

新川　治子 1), 髙畑　陽子 1)

　

要　旨　骨盤外計測法は安全で簡便であることから , 医療技術の進歩した現在においてもその有用性が知られ

ているが ,標準値は 40 年以上変わっていない。そこで本研究は骨盤外計測器を用いて ,現代の成熟期早

期女性の各骨盤径線の変化 , 遺伝的因子や減量，運動の経験と骨盤の形状との関係 , 日常的な不快症状

との関係を明らかにすることを目的とした。結果 , 転子間径に有意な発達がみられるが , その他の径線

に大きな変化はなかった . また , 転子間径 / 外結合線比は拡大したが , 総合的には骨盤のバランスに著

しい変化は認められなかった . 骨盤の発育に出生時体格や遺伝的因子の影響は少なく , 現在の体脂肪率

が有意に関連している . 日常生活上の不快症状のうち下肢のむくみや肩こり , 尿失禁 , 腹部膨満感があ

る女性は , これらの症状のない女性よりも骨盤が大きく , 特に横方向が大きかった . 骨盤痛や易疲労感

のある者は外結合線のみが大きいことが明らかとなった .

キーワード：不快症状 ,骨盤外計測 ,骨盤のバランス ,骨盤の大きさ ,成熟期早期女性

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Introduction　The human pelvis is composed of the coxal

bone, sacrum, and coccyx, with multiple ligaments

that maintain stability. Pelvic development was

extensively researched from the 1970s to the

1990s. Results showed that in women, the pelvis

begins significant growth from the year preceding

menarche, as with height and the long bones, and

continues to grow for at least one or two years after

growth of the long bones has stopped (Araki, et al.,

1985). In terms of pelvic balance, a girl’s pelvis

develops properly in anteroposterior diameter from

age 6 to approximately age 10 and then develops its

transverse diameter. The anteroposterior diameter

is believed to also develop from late adolescence

to early maturity; age 20 to 25. (Araki, et al., 1985;

Onuma, 1977).

　Bone growth is controlled by nutritional and

hormonal factors, and bone stress. The impact of

nutrition on bone growth in Japanese was made

clear in the years following World War II; as

nutrition improved so did Japanese physiques (Araki,

et al., 1980; Araki, et al., 1985). During puberty,

growth hormones and thyroxin cause dramatic

bone growth by acting on epiphyseal plates.

Estrogen, testosterone, and other sex hormones also

stimulate osteoblasts to build bones. As a result, the

epiphyseal plates become thinner and ossified, and

bone growth stops. When a force is applied to the

bone, bone minerals create a minute electric field

which attract osteoblasts. This means that bones are

thicker when a strong external force is applied but

become thin and brittle when external force is not

continuously applied (Martini, et al., 2000). These

demonstrate the essential factors that are crucial in

maintaining bone thickness.

　While many countries have become concerned

with increased rates of obesity, Japan has long

faced the issue of young women who are too thin

(Sugawara, et al., 2009). According to the 2010

National Health and Nutrition Examination Survey

(Ministry of Health, Labour, and Welfare, 2013),

22% of women in their 20s are underweight, which

is markedly higher than other female age groups

or in men. It has been pointed out that the context

for this includes the trend of associating thinness

with beauty and related excessive dieting to lose

weight. Weight loss causes fat reduction that lowers

estrogen production and can cause amenorrhea.

Therefore, 48% of secondary amenorrhea cases

were reported to be anorexia nervosa (Sakakibara,

2011). Meanwhile, birth weight among newborns

has dropped significantly, peaking at 3200g in 1975

and dropping to 3002g in 2013, with an ongoing

increase in newborns who are small for their

gestational age. The increase in females dieting for

weight loss (hereafter, dieting), and for a longer

period of time, has been related to an increase in low

weight newborns.

　Females who have dieted during the pelvic

development period have therefore been presumed to

have less estrogen secretion because of the reduction

in body fat, causing delayed bone ossification due

to delayed or arrested menarche. Poor nutrition,

in turn, has been surmised to cause inadequate

bone development, leading to a small pelvis or to a

pelvis that has a long anteroposterior diameter. In

modern society where lifestyles have become more

sedentary, pelvis development may be positively

affected by exercise such as experienced in junior

high and high school club and sports activities.

Despite these changes in women’s health issues and

lifestyles, very little research has been conducted

on pelvic shape in healthy women in early maturity

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since the beginning of this century. Also, standard

pelvic measurement values (Nakanishi, 2001) have

not been updated since the 1970’s.

　Accordingly, this study aimed to use external

pelvimetry, which was often used in the 1970s,

to measure the pelvis and better understand the

mechanisms of the changes in the length of, and

balance between, the diameter lines from the

standard measurement values, which have been

used for more than 40 years. Also, the relationships

between pelvic shape and genetic factors, as well as

to dieting and exercise that take place from puberty

to early maturity were investigated. In addition, this

study aimed to better understand the relationship

between pelvic size and balance, and the daily

discomfort frequently reported by women in early

maturity and to provide data leading to improved

care that would contribute to a higher quality of life

among women.

Research methods1. Participants

　Participants were women aged 18 to 23 who were

attending university in Hiroshima Prefecture, and

recruited through posters displayed throughout the

campus. Of 163 respondents, 146 were included

in the study analysis; excluding those whose

questionnaires were incomplete.

2. Measurement tools

1) External pelvimetry

　Narrow pelvis and cephalopelvic disproportion

(CPD) are diagnosed using radiography or magnetic

resonance imaging (MRI), which are able to directly

measure the size of the pelvic cavity. However,

performing MRI and radiography examinations

on healthy women have limitations in terms of

cost and safety. In this regard, external pelvimetry

offers a safe, simple, and noninvasive measurement

of bone length obtained by measuring the length

between two points from the skin surface. Though

different from the measured values on radiography

or MRI, the diameter lines, as determined by

external pelvimetry, were strongly and significantly

correlated with pelvimetric sites on radiography as

follows: the interspinal and transverse diameters of

the area of the pelvic inlet (r = .720), the external

conjugate and obstetric conjugatediameter (r =

.730), and the lateral conjugate and anteroposterior

diameter of the midpelvis (r = .733; Masuzaki, et

al., 1991).

　This survey therefore measured external

pelvimetry by using the Martin pelvimeter. Figure 1

shows the measurement sites; the external conjugate

diameter, intercristal diameter, interspinous

diameter, intertrochanteric diameter, and external

oblique diameter. To improve reliability, precise

measurements were taken by researchers who were

midwives, and confirmed by pretest. Measurements

were obtained over one layer of thin clothing.

　The intertrochanteric diameter-to-external

conjugate ratio, which served as the reference for

balance between the transverse and anteroposterior

diameters, was established to better understand

balance. The difference between the intercristal

and interspinal diameters, strongly associated with

platypelloid pelvises, was also investigated. A

principal component analysis established a pelvic

score indicative of the pelvic size. The pelvic score

was abridged into one component, with a cumulative

load of 58.2% and eigenvalue ranging from .629 to

.846.

Figure 1. External pelvimetry (quoted from Nakanishi, M. (2001))

① external conjugate diameter ④ intertrochanteric diameter② intercristal diameter ⑥ external oblique diameter③ interspinous diameter

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2) Measurement of physique

　Physique was determined by measuring height

and weight to calculate body mass index (BMI).

Body fat percentage (HBF-306-W body fat scale,

Omron) was measured by bioelectrical impedance.

Errors in measuring body fat percentage were

minimized by avoiding times immediately after

intense exercise and delaying measurement

approximately 1 to 2 hours after eating.

3) Basic information, lifestyle, and discomfort

　Data were collected by questionnaire for

discomfort and for whether or not participants had

dieting experiences since junior high school. For

discomfort, respondents were asked if they had

experienced any of the 17 symptoms of discomfort

identified by Shinkawa (2009) over the previous

week. Participant physiques at birth and one month

after birth were assessed by obtaining copies

of health records from the Maternal and Child

Health Handbook. Birth mother physiques (for

nulligravidae) after giving birth were also assessed

by data provided by the Handbook.

3. Methods of analysis

　Analysis relied on IBM SPSS Statistics 19.0.

Nakanishi’s (2001) pelvic diameters, widely used

as the standard measurement values in the perinatal

period, were used to compare our measurement

results by performing the test of population mean

with 95% confidence. The relationships between the

pelvic diameter lines, intertrochanteric diameter-

to-external conjugate ratio, the difference between

the intercristal and interspinal diameters, the pelvic

score established by principal component analysis,

and discomfort and experience in weight loss and

exercise were investigated by t-test (unpaired).

Meanwhile, the relationship with physique at birth,

current physique, and genetic factors was analyzed

Table 1. Characteristics of participants N = 146mean SD range

Age (years) 20.3 1.1 18~23Height (cm) 157.47 5.26 141.3~169.8Body fat percentage (%) 25.0 5.2 9.6~41.6BMI (kg/m2) 20.39 1.61 14.4~32.7

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by correlation coefficient and multiple regression

analysis (stepwise). Excessively long participants

were those whose interspinal, intercristal, or

intertrochanteric diameter was longer than the

standard value by 2 cm or more, or whose external

conjugate or external oblique diameter was

longer than the standard value by 1 cm or more.

Excessively short participants were those whose

interspinal, intercristal, or intertrochanteric diameter

was shorter than the standard value by 2 cm or

more, or those whose external conjugate or external

oblique diameter was shorter than the standard value

by 1 cm or more.

4. Ethical considerations

　Participant recruitment posters listed research

objectives, methods of data collection, management

and handling of personal information, and the

method used for reporting results. On the day of

measurement, the same information was explained

verbally and in writing, and written consent was

obtained. This study was approved by the Hiroshima

International University School of Nursing ethics

committee in March 2010, and was conducted in

accordance with the Declaration of Helsinki.

Results1. Features of the participants’ pelvic shapes

　Participants’ characteristics are shown in Table

1. Most participants had a standard physique, with

73.3% having a BMI of 18.5 to less than 25, and

69.2% having a body fat percentage of 20% to less

than 30%.

　The values of the diameter lines measured

in this study were compared against standard

measurement values, and the intertrochanteric

diameter was significantly longer (p < .05). The

interspinal diameter, intercristal diameter, external

conjugate, and external oblique diameter in turn

tended to be short, though not significant (Table

2). Of all participants, 56.2% had one excessively

short diameter line. The platypelloid participants,

in whom the difference between the interspinal and

intercristal diameters was less than the standard

value, accounted for 38.4% of the participants.

Similarly, the ratio of the intertrochanteric diameter

to the external conjugate was greater than the

standard value by 1.5, with some 93.8% presumed

to have a large transverse diameter of the pelvis.

2. Relationship with physique

　In the relationships between the diameter lines,

and pelvic score and physique (height, weight,

BMI, and body fat percentage), a moderate to

strong positive correlation was observed in all the

relationships, excluding the interspinal diameter and

some external conjugate (Table 3). The difference

between the intercristal and interspinal diameters

showed a weak correlation with weight, BMI,

and body fat percentage, with thinner individuals

Table 2. Pelvic size and balance of young women

DiameterStandard

measurement(Nakanishi, 2002)

N=146Average (SD) cm

Excessively short 1)

%Excessively long 2)

%

Sp 23.0 22.40 (1.68) 11.6 8.9Cr 26.0 25.63 (1.87) 13.0 13.7Tr 28.0 31.13 (2.01) 1.4 84.2

Sch 21.0 20.63 (2.01) 34.9 30.1Ext 19.0 18.36 (1.65) 34.9 18.5

Cr-Sp 3.0 3.23 (1.41)Tr ／ Ext 1.5 1.71 (0.14)

Note. Sp: interspinous diameter, Cr: intercristal diameter, Tr: intertrochanteric diameter, Sch: external oblique diameter, Ext: external conjugate diameter

1) Excessively short participants were those whose interspinal, intercristal, or intertrochanteric diameter was shorter than the standard value by 2 cm or more, or those whose external conjugate or external oblique diameter was shorter than the standard value by 1 cm or more.

2) Excessively long participants were those whose interspinal, intercristal, or intertrochanteric diameter was longer than the standard value by 2 cm or more, or whose external conjugate or external oblique diameter was longer than the standard value by 1 cm or more.

Table 3. Relationship with pelvic size and physique N = 146Hight Weight BMI Body fat percentage

Sp .421 *** .298 *** .145 .275 **Cr .315 *** .472 *** .385 *** .450 ***Tr .427 *** .601 *** .463 *** .543 ***

Sch .304 *** .609 *** .540 *** .591 ***Ext .276 ** .727 *** .677 *** .687 ***

Cr-Sp -.082 .274 ** .339 *** .272 **Tr ／ Ext -.152 -.133 -.163 -.133

Pelvic score .451 *** .700 *** .572 *** .659 ***

Note. Pearson’s coefficient of correlation, *p < .05, **p < .01, ***p < .001

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showing a tendency to be platypelloid (r = .27 ~ .34,

p < .01). However, the intertrochanteric diameter-

to-external conjugate ratio, which is indicative of

the balance between the length and breadth of the

pelvis, exhibited no relationship with physique.

　Thus, a multiple regression analysis was

performed, with the pelvic score as a dependent

variable, and height, weight, body fat percentage,

and BMI as independent variables. BMI was

excluded by stepwise procedure. Three models were

extracted, having a multiple correlation coefficient

R2of .5 or higher and a highly accurate prediction

of the multiple regression formula. Therefore, a

model was used that had a high multiple correlation

coefficient and low VIF, with height and body fat

percentage as independent variables (R2 = .532, VIF

Table 4. Relationship between pelvic size, and dieting experience and exercise experience

Dieting experience Exercise experience

Differences from non experienced group (cm) p value Differences from non

experienced group (cm) p value

Sp .33 .25 -.04 .92Cr .37 .22 -.05 .89Tr .79 .02 -.39 .36

Sch .59 .08 -.39 .35Ext .42 .12 -.10 .77

Cr-Sp .04 .86 -.01 .96Tr ／ Ext .02 .33 -.02 .51

Pelvic score .34 .04 -.12 .55

Note. Unpaired t-test

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= 1.044). The standardized coefficients were .329 (p

= .000) for height and .592 (p = .000) for body fat

percentage, and pelvic score was strongly affected

by body fat percentage.

3. Relationship between physique at birth and

genetic factors

　No significant relationships were observed

for height and weight at birth and various pelvic

diameter lines and pelvic score. Height at the one-

month health check was not noted in one third of the

participants’ Maternal and Child Health Handbooks.

We examined only those 107 participants who did

have data. We observed weak positive correlational

relationships of height with intercristal, interspinal,

and intertrochanteric diameter (r = .24 ~ .35, p

< .05). In addition, we observed weak positive

correlational relationships of the mother's height

with intercristal, interspinal, and external conjugate

diameters, and the mother's weight with intercristal

and external conjugate diameter (r = .26 ~ .27, p <

.01).

4. Relationship with previous lifestyle

　Examining the relationship between pelvic size,

and dieting and exercise experience, we found that

those with dieting experience tended to have larger

pelvises, with significant differences particularly in

intertrochanteric diameter (t (141) = 2.31, p = .02)

and pelvic score (t (141) = 2.04, p = .04). However,

no relationship was observed between exercise

experiences since junior high school, such as group

activities, and the pelvic size or balance (Table 4).

5. Relationship with discomfort in daily life

　Of the 17 symptoms causing discomfort in daily

life, a mean of 6.5 (SD 2.8) symptoms per participant

was recorded. The most frequent symptoms were

fatigability, leg coldness, stiff neck, irritability,

abdominal bloating, and swelling, with the first five

top five symptoms observed at least 80% of the

time.

　Therefore, the relationships between individual

symptoms, and pelvic size and balance were

examined (Table 5). The results showed that those

with leg swelling or stiff neck tended to have larger

pelvises and had significantly larger transverse

Table 5. Relationship with pelvic size and discomforts

incidence rate(%) Sp1) Cr1) Tr1) Sch1) Ext1) Tr／Ext1) Cr-Sp1) Pelvic1) score

Pelvic pain 16 (11.2) 1.16*Stiff shoulder 89 (62.2) .07** .49*

Abdominal compression 83 (58.0) .67*

Incontinence of urine 7 (4.9) .52*

Varix 2 (1.4) -.26**Cold hands 74 (51.7) -.57*

Cold hip 29 (20.3) .96* .77*Swelling of leg 77 (53.8) 1.06**

Fatigability 111 (77.6) .85*

Note. Unpaired t-test, *p < .05, **p < .01, ***p < .0011) Numbers indicate differences of mean from those without discomforts.

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diameters. Those who had urinary incontinence

and abdominal bloating also showed a tendency to

have larger pelvises and larger transverse diameters.

Those with hip coldness or pelvic pain had large

pelvises, with many having a long anteroposterior

diameter. Participants with pelvic pain or fatigability

had a large first external conjugate but had no other

diameter line showing a significant difference from

those without symptoms.

Discussion　This study used external pelvimetry, frequently

employed in the 1970s and 1980s, to better

understand pelvic size and balance in contemporary

women in early maturity, and to examine the

influencing factors and their impact on daily life.

Results show that intertrochanteric diameter is

longer than the standard value, all other diameters

were shorter than the standard, with a change

believed to have taken place in the pelvic balance.

The impact on life was also clarified.

1. Features of pelvic shape in contemporary women

　In clinical settings, narrowing and imbalance

have been observed in women’s pelvises. This study

found a tendency for each of the pelvic diameter

lines to be shorter than the standard value, and only

the intertrochanteric diameter (mean, 31.1 cm)

was significantly longer than the standard value

(28 cm). Other recent investigations have reported

similar results; Minohara, et al. (2003) reported a

length of 29.7 cm and Doi, et al. (2012) reporting

30.7 cm. The only negative aspect of using external

pelvimetry is the possibility of errors committed

by the measurer. According to Masuzaki, et al.

(1991), the error at the intertrochanteric diameter

is smallest with a mean of 3.0% of the coefficient

of variation, so the intertrochanteric diameter could

be said to have been increased. However, a survey

of adolescent girls conducted in 1970 (Tokue,

1970) revealed that the intertrochanteric diameter

already exceeded 30 cm at the age of 18. The

intertrochanteric diameter is the length between the

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left and right greater trochanters. Thus, in terms

of position, the intertrochanteric diameter is less

susceptible to changes in the balance between the

anteroposterior and transverse diameters associated

with development of the pelvis, for which reason it

is similar to the values reported in the 1970s.

　Women’s pelvic areas can be classified into

the anthropoid, circle, and platypelloid types.

Narumoto, et al. (2013) investigated changes in

type distribution in women’s pelvic inlet areas via

radiography at the end of pregnancy, and found

that the most common type in the 1960s, circle,

had fallen from 60% to 45% of pelvic areas, and

an increase of from 8% to 47% in the anthropoid

type, which has a longer anteroposterior diameter.

Because the intertrochanteric diameter was extended

in this study, there was a higher value for the ratio

of the intertrochanteric diameter and external

conjugate, which has been long used to assess the

balance between the anteroposterior and transverse

diameters of the pelvis. The mean interspinal

diameter, which has a high correlation with the

transverse diameter of the pelvic inlet area, was

shorter, though not significantly so. For reference,

when the ratio between the interspinal diameter and

external conjugate (standard: 23 / 29 = 1.21) and the

ratio between the intercristal diameter and external

conjugate (standard: 26 / 19 = 1.37) were examined,

the proportion of participants for whom the ratio

was smaller than the standard value were 45.9%

and 41.8%, respectively. In this study we see that

contemporary women’s pelvic inlet areas cannot be

said to have become more slender and elongated.

Although the transverse diameter might appear

larger than the extension of the intertrochanteric

diameter when general indices are used, no major

change from the standard values was observed in the

balance of the pelvic inlet area.

　Meanwhile, the intertrochanteric diameter is

strongly related to the anteroposterior diameter

of the midpelvis (Masuzaki, et al., 1991), and

the anteroposterior diameter of the midpelvis is

believed to have become larger. Originally, the

oblique diameter was greatest for the midpelvis. For

this reason, the fetus can turn the second rotation

unencumbered during delivery. However, to say

that the midpelvis had a greater anteroposterior

diameter would also mean that the second

rotation is completed well before the fetal head

reaches the narrow pelvic part, and this could

be a cause of abnormal rotation. According to

Maeda, et al. (1998), the cesarean delivery rate for

intertrochanteric diameters of 28 cm and greater

is 5.8%. There is also the possibility that in the

future an increase in women with more developed

intertrochanteric diameters could increase the rate of

cesarean delivery.

　As has been noted (Sakamoto, et al., 1998),

screening contemporary young women for narrow

pelvis due to conjugataveraobstetrica is not

meaningful. This means that cesarean delivery rates

for women with an external conjugate of less than

17.5 cm, or with a conjugatavera obstetrica of less

than 9.5 cm, these two having been standards in the

past, are lower than for women with an inlet area

transverse diameter less than 10.5 cm (C-section

rates for the above are 5.2%, 40.0%, and 72.7%,

respectively). Maeda, et al. (1993) have also

reported more women taller than the standard height,

which indicates that measured values are longer

than the standard values, and that balance is also

important. This suggests that the standard values

need to be reviewed for contemporary women,

and that each of the diameter lines also need to be

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reassessed by balance.

2. Factors associated with pelvic size

　The length of each of the pelvic diameter lines

have been strongly related to height, and in clinical

practice the standard is to consider assessing women

for narrow pelvises, and therefore high-risk delivery,

if they are shorter than 150cm, and especially if they

are shorter than 145cm. However, in recent years,

questions have emerged regarding the relationship

between height or physique and pelvic size (Chihara,

et al., 2010; Doi, et al., 2012). The physiques of

Japanese women have improved rapidly, mostly in

height, from the first half of the 1900s until 1990.

Thus, when compared to the pelvises of women from

Japan’s Meiji era (1868-1912), mean height increase

has had a considerable impact on the development

of each of the diameter lines (Minohara, et al.,

2003). Since 1990, however, women’s physiques

have gone unchanged (Ministry of Internal Affairs

and Communications, 2013). In this study, the

relationship of height to each of the diameters was

weaker than those of body fat percentage (r = .45

– .69, p < .001) and BMI (r = .39 – .68, p < .001).

The lower the weight, BMI, or body fat percentage,

the smaller the difference between the intercristal

and interspinal diameters; thus, the thinner women

become the more they tend to be platypelloid.

　A girl’s height and pelvic size are greatly

influenced by her birth mother’s height, until age

14, and then are influenced by paternal height

thereafter (Togo, et al., 1988). This survey, which

studied female students, found a weak correlation

between each of the pelvic diameter lines and the

birth mother’s height or weight. No correlation to

the respondent’s own physique at the time of birth

was found. These results show that pelvic size and

balance is influenced more by nutrition factors than

by received genetic attributes or birth weight and

height. Therefore, in future screening for narrow

pelvis it is recommended to use BMI or body fat

percentage instead of height.

3. Impact on daily life

　As also shown in this study, contemporary women

in early maturity often have discomfort in their

daily lives. Therefore, this study considered whether

pelvic size or balance was related to the onset of

discomfort. In particular, leg swelling or numbness,

coldness, and varicose veins are clinically known

to be related to disturbances of the autonomic

nervous system and poor circulation in the pelvis.

We therefore predicted we would find more women

with a relatively small pelvis or with a pelvis that

tends to be flat. Unexpectedly, the results of this

study show that women with large pelvic diameter

lines have a higher incidence of these discomforts,

and in particular, there are numerous women with

development reaching the transverse direction.

Therefore, the relationship with pelvic size requires

future investigation.

　Women with pelvic pain or fatigability had

larger first external conjugates. This survey did

not measure distortion of the pelvis, but the fact

that diameter lines, other than the first external

conjugate, had no difference from participants

without discomforts suggests pelvic distortion.

Minohara, et al. (2003) have reported a lack of

correlation between pelvic distortion in daily habits

such as holding a bag, sitting, or having the center of

gravity concentrated on one side. Causes of pelvic

distortion will require further examination.

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4. Implications for nursing and midwifery

　A woman’s pelvis is important for protecting and

nurturing a fetus for 9 months, but at the same time,

it serves as a birth canal during birth. Therefore, its

shape is of considerable obstetric importance. As

medical technology has advanced it has become

possible to measure pelvic shape more accurately.

The amount of radiographic exposure has also been

successfully improved, with no substantial effect

observed on the fetus or on pregnant women in late

pregnancy. Nonetheless, radiography should not be

used in all pregnant women. Low height is used to

identify high-risk groups, however, women who are

slender or have a low body fat percentage have also

been considered as being at high-risk.

　Data on the application of external pelvimetry

have been accumulated over several years and

is now considered a safe and simple assessment

method. The present results suggest the need to

update to new standard measurement values and

make indices for assessing balance by collecting

data on contemporary women.

5. Limitations of the study and future challenges

　Japan’s contemporary women are very self-

conscious of their physique, in particular weight,

and 40% of our participants had dieted for weight

loss. People who diet generally have repeatedly

done so since youth, and secondary amenorrhea,

common in adolescence, has been related to excess

weight loss. Tokue (1970) noted that with secondary

amenorrhea, the pelvic diameter lines were smaller

than the standard, and the increasing dieting time

during youth is presumed to substantially impact the

health of future mothers and the development of the

pelvis by which the next generation will be born.

　In this study, body fat percentage was shown to

be considerably related to pelvic size and balance in

women in early maturity, so an attempt was made

to also examine the relationship with weight loss.

Results show that women who had dieted for weight

loss had larger diameter lines. However, the BMI

and body fat percentage of those with experience

dieting were significantly higher than those who had

never dieted, and results during weight loss were

not surveyed. Therefore, we could not conclude

that dieting during pelvic development is associated

with delayed development of the pelvis. Future

improvements to the questionnaire would contribute

more meaningful assessment.

　In conclusion, this study has clarified the

following regarding the assessment of pelvic size

and balance by external pelvimetry: contemporary

women in ear ly matur i ty show signif icant

development of the pelvis in the intertrochanteric

diameter but no major changes in other diameter

lines. Development of the intertrochanteric diameter

is associated with a higher intertrochanteric

diameter-to-external conjugate ratio, but the overall

pelvic balance showed no remarkable change. Pelvic

size and balance were only slightly influenced

by physique at birth and by genetic factors, and

the current body fat percentage was of significant

relevance to pelvic size. Of the forms of discomfort

in daily life, women who have leg swelling, stiff

neck, urinary incontinence, or abdominal bloating

have larger pelvises, especially in the transverse

direction, than women who do not have these

symptoms. Women with pelvic pain or fatigability

had larger external conjugates.

Acknowledgments　We wish to thank all the participants who

cooperated with this s tudy and Hiroshima

─ 24 ─


International University’s Yuka Saito and Maki

Sugino for their assistance. This study received a

special research grant from Hiroshima International

University.

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