Clin. RadioL (1978) 29, 85-90

C O M P A R A T I V E P E L V I M E T R I C M E A S U R E M E N T S IN N I G E R I A N AND W E L S H WOMEN

T. M. KOLAWOLE, S. P. ADAMU and K. T. EVANS

From the Departments of Radiology and Statistics, University of lbadan, Nigeria, and the Department of Radiology, Welsh National School of Medicine, Cardiff, Wales, UK

The authors compared the pelvic measurements of a group of Nigerian women with those of a similar group of Welsh women. The Nigerian pelvis is smaller than the Welsh especially when account is taken of the Nigerian woman being taller. Base-line data for radiologists working in Nigeria are provided.

Clinical examination of Europeans and Nigerians reveals physical differences in the external appearances of the pelvis of the two groups. The European pelvis is broad from side to side and flat posteriorly with little soft tissue posterior to the sacrum. However, the Nigerian pelvis appears small from side to side with excess fat and soft tissues on the sacrum posteriorly and relatively little soft tissue on the lateral aspects of the hips compared to their European counterparts. It is reported that there is a marked acuteness of the himbosacral angles in Nigerians (Lister, 1960). Those who have practised obstetrics in Nigeria as well as in Europe have commented on the shallowness of the pelvis and the high incidence of obstructed labour in Nigerians and the different courses in the progress of labour between the two groups (Lister, 1960). Therefore, a comparative analysis of the pelvic measurements in both Nigerians and Welsh parous women was under- taken in order to verify these clinical impressions, and also to provide some base-line data for radiologists and obstetricians working in Nigeria. The choice of the two groups was dictated by the hospitals in which one of the authors has practised. Hitherto, no detailed radiological (pelvimetric) study has been made on the Nigerian female pelvis.

MATERIALS AND METHOD

Fifty consecutive female patients in Royal Infir- mary, Cardiff, and fifty-one consecutive cases in University College Hospital, Ibadan, referred for pelvimetric examinations were selected. Such patients who were in their third decade of life had their heights recorded.

A single lateral view of the pelvis was obtained in each patient with the patient standing upright against a Bucky grid and with a graduated metallic rod graduated in centimetres placed in the gluteal crease (midsacral line), horizontal to the floor, parallel with the spine and fdm and pointing in an antero-postefior direction (Colcher-Sussman method, 1944).

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A 10 cm portion of a metal rod was then measured on the radiograph and from this the magnification factor for the pelvic measurements was obtained. Since the metal rod was in the same rnid-sagittal plane of the body and as far from the fihn or the tube as the antero-posterior midline diameters of the pelvis, its magnification factor would be the same as those of the antero-posterior diameters of the pelvis. The pelvic measurements were therefore divided by this magnification factor to obtain 'the true pelvic measurements, that is the antero-posterior measure- ments of the pelvis in the sagittal midline plane. Measurements from the lateral radiographs were taken as shown in Fig. 1.

The measurements of the antero-posterior dia- meters of the pelvic inlet, midplane and outlet were taken, using the standard anaton~cal landmarks as indicated in Fig. 1. The posterior depth of the pelvis is defined as the distance between the sacral pro- montory and the sacrococcygeal junction and the sacral height the greatest perpendicular from the inner aspect of the sacrum to the line depicting the posterior depth of the pelvis. The angle of the sacral curve is the angle subtended by this line depicting the posterior depth at the point where the line of the sacral height touches the inner aspect o.f the sacrum.

Measurements of the lumbosacral angle and the angle of the pelvic inlet were made according to the method of Ferguson (1949) and as depicted in Fig. 1.

Measurements were made of 10 variables and the means, ranges and standard deviations of these variables have been calculated and presented in Table 1 for a preliminary study. For each variable, 't' test was used to compare the difference between the two groups.

RESULTS

The mean height of the Nigerian women was 158.73 cm (range 144-183 cm) whereas those of the Welsh women was 154.38 cm (range 137-165 cm). The difference in heights is very significant (t = 3.16,

86 C L I N I C A L R A D I O L O G Y

A_ Upper inner margln of the publc symphysls B= Upper inner borders of the f irst Sacral vertebra C = Lower Inner margin of pubic svmphysis D = Ischial spines F = The point at which the line CD touches the inner aspect o f the sacrum H = Lowest anter ior margin of the last sacral segment (points F&H sometimes

overl ie) G = Midtuberal point M= Anterior supenor i(iec sp ine N = Outer border of pubic symphysis

LIfO = Line d rawn over the superior artLca[ar surface of first sacral spine ST = Perpendicular drawn to the line MN hor izontal hne

0 •

AB pelvic inlet anteropostenol dlClmeter AC = Anterior depth of the pelwc cawty

CDF : PeLvic Midpiane anterepostenor diameter GH : Pelvic outlet anteroposterlor diameter Rtl Posterior depth e l pelwc cavity XY Maximum perpendicular drawn from the inner aspect of the sacrum to

[he hne BH (Sacral hetghl) LBOS = Lumbosacral angle

BAP Angle of inchinabon el the pelwc Inlet

Fig. 1

It is therefore seen that in all the posterior measurements, the pelvis of the Nigerian women are smaller than those of the Welsh, even though the Nigerians are significantly taller. The difference is most significant at the pelvic inlet; and least sig- nificant at the pelvic outlet.

The inclination of the pelvic inlet was significantly greater in Nigerians than in the Welsh (t = 3.08, P < 0 . 0 1 ) the means being 55.43 ° and 59.86 ° res- pectively. Moreover, the mean himbosacral angle in the Welsh was 146.05 ° (range 125-163°) , compared with 148.45 ° in Nigerians (range 127-165°) . The difference is not significant (t = 1.31, P > 0.1).

DISCUSSION

The approach adopted above is not quite ade- quate. In this situation, 10 variables are involved. To compare one variable at a time may be misleading because the variables are likely to be interrelated as they exist in the individuals simultaneously. There is the need to employ a method which takes note of this inter-relatedness of variables. To do this, we have employed the generalised form of ' t ' test statistic when there is more than one variable. This is Hotelling's T 2 statistic for comparing two samples when there are many variables.* 7 a statistic is related to Fisher's F as follows:

P < 0 . 0 1 ) , with the Nigerian women studied being taller than the Welsh.

The mean anterior depth of the pelvis in Nigerians was 8.63 cm (range 7 .35-9 .83 cm) and 9.12 (range 7 .83-10 .90 cm) in the Welsh. This difference is very significant (t = 3.80, P < 0 . 0 0 1 ) . Of greater signifi- cance at the same level are the measurements of the posterior depths (the straight sacral length) which had a mean of 10.28 cm in the Nigerians (range 7 .0-11.9 cm) and 11.32 cm (range 8 .99-13 .94 cm) in the Welsh.

The mean antero-posterior diameter of the pelvic inlet in Nigerians is 11.07 cm (range 8 .35-13.2 cm) compared with a mean of 12.15 cm (range 9 .54-14 .5 cm) among the Welsh (t = 5.36, P < 0.001).

The difference in the midcavity antero-posterior measurements are also quite significant at 1% level; t being 3.18. The values of the midcavity antero- posterior measurements are a mean of 11.26 cm (range 9.7 14.5 cm) m the Nigerians and a mean of 11.93 cm (range 9 .54-15.5 cm) among the Welsh.

The mean antero-posterior diameter of the pelvic outlet in the Nigerians was 7.81 cm (range 5 .12-10.30 cm) and 8.18 (range 4 .15-11 .46 cm) in the Welsh. There is no statistical difference in the two groups at 10% level of significance, t being 1.57.

h i + h e - m - - 1 F = T 2

(F/1 + ] ~ 2 - - 2)m

where n 1 = sample size of group 1

n2 = sample size of group 2

m = number of variables

The F test is employed with m and n~+n2 m 1 degrees of freedom. The calculated value in the present situation gives F = 11.40 with 10 and 90 degrees o f freedolrL

This is highly significant at 0.001 level. As a result of this and the marked differences shown by some of the variables above for ' t ' test, we can conclude that the two groups are significantly different.

Equipped with the above, specific details can now be discussed. It is well known that in Nigerian females the engagement of the foetal head rarely occurs until the end of the first or onset of the second stage of labour and is uninfluenced by the rupture of the membranes. This late engagement does not prolong labour (Lister, 1960), However, obstructed labour is

* Morrison, D. F. (1967). Multivariate Statistical Methods. McGraw-Hill, New York. 125.

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88 CLINICAL R A D I O L O G Y

Table 3

True conjugate (cm) Brim area - (cm2)

Brim index

Uganda (Atlbrooke and Sibthorpe, 1961) 9.97 87.2 87.6

Scotland (women under 5 ft) (Bernard, 1952) 10.77 106.8 85.1

Table 4 - Comparison of mean maximum head diameter and body weight in Ganda, Scottish and Nigerian newborn infants

No. Mean birth s.d. Mean birth weight ~ d. head circum- (cm] (lb oz) (oz) ference (cm)

Ganda male 326 33.78 1.28 7 0 14_4 Ganda female 328 33.24 0.96 6 11 12.8

Pooled 654 33.51 1.31 66 13.6

Scottish male 243 34.60 1.39 7 9 18.0 Scottish female 209 33.90 1-26 7 5 15.0

Pooled 452 34.25 1.33 7 7 16.5

Nigerian male 48 34.96 1.221 7 1 13.65 Nigerian female 52 34.52 1.342 6 7 19.71

Pooled 100 34.73 1.281 6 9 16.68

quite common in Nigeria, and is the largest individual factor in both maternal deaths (27.2%) and stillbirths (18.8%). Furthermore, 67% of all cases of obstruction as well as 70% of maternal deaths are due to cephalopelvic disproportion at the pelvic brim (Lister, 1960). Obstructed labour in Britain and America is largely due to uterine dystocia but dystocia is rare in Nigerians (Lister, 1960) and amongst the Bantus of South Africa (Heyns and Shippel, 1946).

It is thought that one of the factors which may be responsible for this late engagement is the steep inclination of the pelvic brim and the associated marked lumbar lordosis. Furthermore, clinical examination reveals the Nigerian pelvis is shallow, with the sacral promontory being easily reached in the majori ty of women.

Up till now no definite radiological series have been carried out on the pelvimetric measurements of the Nigerian women. It is against this background and assumptions that the present study was carried out.

The pelves of 50 Welsh and 51 Nigerian women in the third decade of life have been studied in this series. These numbers appear small but are adequate when viewed against the background of other studies, 90 cases by Allbrook and Sibthorpe (1961) and 66 cases by Heyns (1946). In 1961, Allbrook and Sibthorpe studying the pelvic measurements of Ganda women, compared the results obtained in 90 cases studied in a radiological series with 32 cases studied

in an osteological series. The two series correlated very well with little or no difference in the mean values obtained. Therefore, 50 as a number appears reasonable, and this is borne out by the statistical results of this study.

The mean height of the Nigerian women studied was 158.7, whereas that of the Welsh was 154.4 cm. This result is significant as it re-emphasises the smallness of the Nigerian pelvis in all its dimensions. That is, if adequate account is taken of the relative tallness of the Nigerian female, the measurements of the Nigerian pelvis of the same height as those of the Welsh would still be smaller than those obtained.

Pelvimetric measurements have only been recorded on women who were referred for pelvimetric examination for special reasons. These women are expected to have smaller pelves than women from the general population. Comparable controls for the general population, i.e. those with normal pregnancy, would have made inferences more general but could not be justified ethically.

The 100 Scottish women studied in 1952 by Bernard were all under 150 cm, and yet all the measurements of the pelvic brim were significantly bigger than those of relatively taller Ganda women of mean stature of 150 cm (Table 3) (Sibthorpe and Allenbrook, 1958). The radiological methods used in evaluating the pelvic measurements are comparable but not identical to those of previous authors, yet. the

P E L V I M E T R I C M E A S U R E M E N T S 89

results suggest the pelvis of those of African descent is narrower in all its dimensions that those of the European.

The antero-posterior diameters of the pelvis are significantly smaller in the Nigerian than the Welsh: the most significant difference is in the sagittal diameter of the pelvic inlet which was tested at 0.01% level of significance, whilst the sagittal diameter of the pelvic outlet is the least significant at 10% level of significance.

These results are similar with those of other workers in Africa (Allbrook and Sibthorpe, 1961; Sibthorpe and Allbrook, 1958; Heyns and Shippel, 1946) as shown in the Table 2. The African viz. the Ugandan, Gandas, the South African Bantus and the Nigerians, all have shorter sagittal diameters of their pelvic inlets and midplanes as compared with Euro- peans (the English and the Welsh). Similar results were obtained when Kaltreider in 1954 carried out a mass pelvimetry series in Baltimore (USA). He found that in 10.7% of the Negroes, the pelvis was con- tracted as compared with 1.08% of the whites.

When comparing the pelvis of Scottish women with those of the Ugandans, Bernard (1952) found that a small pelvis was more common among those under 5 ft and who were mainly from the lower social grades. It is therefore suggested that the relative smallness in the pelvis of the Nigerian females (all of whom in this study were from the lower income group) may be partly related to malnutrition in early life.

Comparative study of the newborns of the Gandas in East Africa and the Scots suggest that the mean birth weight and head circumference show a very slight statistical difference at a level when P = 0.001 (Ellis, 1951). Heyns and Shippel in 1946 studied the weights and dimensions of the skull of the children in South Africa and found that the differences between the Bantu and European foetal heads at term is insignificant and that evidence has not been found to prove that the Bantu newborn has a smaller head than the European at birth. There is a correlation between the foetal weight and the foetal skull dimensions. The mean birth weight and head circumferences of the Nigerian newborn is similar to those of the Scots and Gandas (Table 4). Since successful labour depends on three main factors comprising the pas- senger, the passages and the power, it can therefore be concluded that in general the varying courses of labour in the different races depends mainly on the powers of contraction and the dimensions of the passages (peMs) and much less on the size of the passengers, that is the dimensions of the foetal skull. Moreover, the late engagement of the head in the Nigerian can therefore be attributed to the narrow-

ness of the Nigerian pelvis and the steep inclination of the pelvic inlet. Heyns and Shippel in 1946 stated that it is the quality of the powers of the uterine contractions that offers an explanation to the success- ful labour in the Bantus which exhibit pronounced pelvic contraction. In the Nigerian also, dystocia is rare (Lister, 1960).

The effective depth of the true pelvis or the length of the bony birth canal is a factor of importance in the mechanics of labour. The Nigerian pelves are shallower than those of the Welsh as judged by the significantly smaller straight sacral lengths (posterior depth) and the symphysial measurements (anterior depths). These facts are borne out by clinical ex- perience in the easy palpability of the sacral pro- montory in the Nigerian females (Lister, 1960). The shallow pelvis or short bony birth canal is also a feature of the Gandas in Uganda (Allbrook and Sibthorpe, 1961) and the Bantus in South Africa (Sibthorpe and Allbrook, 1958).

The inclination of the pelvic inlet is directly related to the lumbosacral angle, because if a patient bends backwards thus making the lumbosacral angle more acute, the pubic symphysis is elevated with consequential elevation of the plane of the pelvic inlet which then approaches the horizontal. A dimi- nution in the lumbosacral angle reduces the angle of inclination of the pelvis.

This greater inclination of the pelvic inlet in the Nigerians supports popular obstetric belief; and with the narrower sagittal diameter of the pelvic inlet conjointly explfiin the marked delay in the en- gagement of the foetus in Nigerians as compared with Europeans.

The angle of the sacral curve is less obtuse in the Nigerian than in the Welsh. This indicates that the sacrum is more hollow in the Nigerian pelvis. A hollow sacrum is more conducive to good labour than a straight sacrurrL In the European the majority of the pelvic contractions is at the midcavity.

Only the mid - sag i t t a l (antero-posterior) measurements have been evaluated in this study. Transverse measurements of the pelvis and the sub- pubic angle have not been done. This was unavoidable as this study was retrospective; and the method of pelvimetry in one of the hospitals is mainly confined to the lateral pelvimetry technique. Kaltreider in 1954 stated that in 10.7% of the Negro population, the major problem was one of pelvic inlet contraction and that the majority of these were due to transverse contraction of the pelvic inlet. In the white race studied at the same time, only 1.08% showed pelvic contractions, mainly mid-plane contractions. These fmdings correlate with those of Allbrook and Sib- thorpe (1961) and Heynes and Shippel (1946) and

90 CLINICAL RADIOLOGY

therefore a more comprehensive and prospective study to include the transverse diameters and the areas of the planes of the pelvis in Nigerian correlated with the data on the outcome of labour (viz. duration of l a b o u r , method of delivery and foetal measurement), is indicated and has begun.

REFERENCES

AUbrook, D. & Sibthorpe, L M. (1961). South African Journal of Medical Science, 26, 73- 83.

Bernard, R. M. (1952). Edinburgh Medical Journal, 1-16. Colcher, A. E. & Sussman, W. (1944). American Journal of

Roentgenology, 51, 207-214.

Ferguson, A. B. (1949). Roentgen Diagnosis of Extremities and Spine. Paul B. Hoeber, Inc., New York.

Heyns, O. S. & Shippel, S. (1946). Journal of Obstetrics and Gynaecology of the British Empire, 53, 405-409.

Ince, J. G. H. & Young, M. (1940). Journal ofObstetries and Gynaecology of the British Empire, 47, 130-190.

Kaltreider, D. F. (1954). Journal of Obstetrics and Gynae- cology, 4, 322-330.

Lister, U. G. (1960). Journal of Obstetrics and Gynaecology of the British Empire, 67, 188-198.

Morrison, D. F. (1967). Multivariate Statistical Methods. McGraw-Hill, New York.

Nicholson, C. (1938).Journal of Obstetrics and Gynaecology of the British Empire, 34, 950-984.

Slbthorpe, E. M. & AUbrook, D. B. (1958). Journal of Obstetrics and Gynaeeology of the British Empire, 65, 600-605.