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The mark-7 intrauterine sound — an accurate determinant of uterine axial length
CONTRACEPTION
THE MARK-7 INTRAUTERINE SOUND - AN ACCURATE DETERMINANT OF UTERINE AXIAL LENGTH
N. D. GOLDSTUCK Marie Stopes House Well Woman Centre 108 Whitfield Street London WIP 6BE, England
ABSTRACT The axial uterine length of 60 nulliparous patients has been measured using a standard Galabin sound and a new flexible disposable sound (Mark-7). In 47 patients the values obtained with the plastic sound were between 0.25 cm to 0.5 cm greater than the values obtained with the metal sound. The flexible plastic sound values are probably larger because this sound is able to follow uterine axial curvature. The element of parallax error which is inherent in using metal sounds is avoided by use of a sliding half-collar at the distal end of the instrument, which can be moved against the cervix allowing fixed measurement. This instrument should be a useful adjunct to intrauterine device research and usage where the relationship of uterine length to device performance is being considered. Correspondence should be addressed to:John Wyeth & Brother Ltd., Wyeth Laboratories, Huntercombe Lane South, Taplow, Maidenhead, Berks, England Accepted for publication September 4, 1979
OCTOBER 1979 VOL 20NO. 4
359
CONTRACEPTION
INTRODUCTION
The clinical determination of uterine axial length is usually by measurement with a Galabin or similar rigid metal sound. The graduated end of the sound is angled at approximately 45 degrees to the horizontal. This type of sound will therefore measure uteri flexed (either forward or backward) at about this angle most accurately. The inaccuracies which arise in the measurement of uteri which are not flexed in the region of this angle probably result from the mismatching of the sound to the uterine axial curvature. The distal tip of the sound thus fails to reach the uterine fundus. The inaccuracy due to this factor is probably fairly small. A further inaccuracy often derives from the operator not being able to read the probed length once the sound has been inserted into the uterus. The presence of blood or sufficient mucus in the cervical canal or on the cervix may help in this regard, if present; alter-natively an estimate of the depth to which the sound has been passed has to be made. This is often erroneous and compounded by the error of parallax. The above inaccuracies are of limited importance in most clinical situations. While initiating a trial of intrauterine device usage in patients with small uterine axial length (<6 cm), it became imperative to make accurate measurements. The difficulties in using standard metal sounds are compounded by the fact that (i) they are usually marked from 6 cm onwards only & (il)the first 4-5 cm of these sounds are curved and therefore unsuitable for making measurements of small uteri which are only slightly or very acutely flexed.
METHODS
Uterine axial length measurement was made using a Galabin sound. This reading was followed hy taking a reading with the ~ k - 7 (G. D. Searle & Co.) sound. This is a sterile packed, disposable, flexible, polypropylene sound, the end of which is ball tipped to avoid causing uterine perforation.
360
OCTOBER 1979 VOL. 20 NO. 4
CONTRACEPTION
The distal end is enclosed by a flanged half-collar whose position can be stabilised by depression after being pushed up against the cervix. Axial uterine length is then read off a scale on the posterior aspect of the sound which is exposed through a window in the half-collar (Figure i). A second method was occasionally used. This is based on the use of the inserter tube of the Progestasert system. The device itself was discarded and the open end of the tube sealed with inert epoxyresin. It was resterilised in O.i per cent benzalkomium chloride for 24 hours. Uterine axial length could be read off the position of the arm-cocker along the graduated stem. This instrument is flexible and incorporates a 25 degree curve, and is thus very suitable for accurate measurements in highly flexed uteri. Care must be taken to allow for the length of the cervical seeking tip of the Progestasert itself, which should be added to the values which are obtained. Nulliparous patients with clinically small uteri were sounded in the usual way. A vulsellum was applied to the anterior lip of the cervix to stabilise the position of the uterus but no downward traction was exerted. Sounding with the metal sound preceded sounding with the Mark-7 sound. This procedure ensured objectivity as the reading obtained with the metal sound was first noted. The subsequent reading which is obtained with the Mark 7 sound cannot be made until the Mark-7 has been inserted, the halfcollar position fixed and the instrument withdrawn from the uterus. As the measurement scale is situated on the posterior aspect of the Mark-7, the reading obtained with the metal sound cannot influence that obtained with the Mark-7. This does not apply to the Progestasert inserter method, as the scale is on the anterior aspect of the tube. Occasionally resounding with the metal sound was performed to ensure that the flexible sound was not breaking down endometrial tissue, e.g. synechiae, etc. On all occasions(ten), the conventional sound gave the same reading before and after the use of the plastic sound. This procedure was therefore abandoned to avoid unnecessary passage of instruments into the uterine cavity. Only patients whose uteri sounded less than 7 em with the Mark-7 were considered eligible for the study.
OCTOBER 1979 VOL. 20 NO. 4
361
CONTRACEPTION
Fig. 1 (from left to right). The posterior aspect of the Mark-7 sound illustrating the ball tipped end (A) and the dual distal (B) and proximal (D) stales. The latter is in black relief and visible through a windew in the half-collar (C), and is the one that is normally used. Two side views of the Mark-7 showing the half-collar in the movable (E) and in ~he depressed fixed position (F). ~The diagram is drawn to scale in the longitudinal direction only).
362
OCTOBER 1979 VOL. 20 NO. 4
CONTRACEPTION
RESULTS
The results obtained from 60 patients are illustrated in Table I. These results indicate that the Galabin sound underestimates uterine axial length by between 0-0.75 cm as compared to the Mark-7 sound. Too few measurements were made with the Progestasert inserter method for a strict comparison with the Galabin sound, but all measurements obtained were equal to or greater than those obtained with the latter, again co~:irming its tendency to underestimate uterine axial _ ngth in the range of 5-7 em. As the Mark-7 scale is graduated to the nearest r only, it is not possible to take readings to an accuracy of less than a quarter of a centimetre. The thirteen readings which were less than this amount different from the aletal sound reading~were biased against the Mark-7. These results, however, remain highly statistically significantly different (Sign test, P
TABLE I MEASUREMENT OF TOTAL UTERINE AXIAL LENGTH IN 60 SUBJECTS
Number of measurements
*Difference in reading between plastic and metal sound (cm)
13
0
41
0.25 - <0.5
6
0.5
- <0..25
0.75
*Readings are determined as plastic sound value minus metal sound value in all cases.
OCTOBER 1979 VOL. 20 NO. 4
363
CONTRACEPTION
DISCUSSION
These measurements have not been compared and correlated with an independent method of measurement, e.g. hysterography. Nevertheless, since the readings with the flexible Mark-7 sound tend to 'over-read' the axial uterine length;it is reasonable to assume that these measurements are closer to the tr~e uterine axial length, as uterine flexion is variable and can be accommodated by the flexible, but not by the metal, sound. The latter will give most accurate readings of axial length at uterine flexion in the range of 40-45 degrees. At this degree of flexion the readings obtained on the two types of sound will presumably be equal, accounting for the observations in Table I. The plastic sound would follow uterine curvature and lover-read' at angles significantly larger or smaller than 40-45 degrees. These results suggest that flexible sounds are more accurate than rigid metal ones insofar as assessing total uterine axial length is concerned, The latter point must be stressed as recent work by Hasson(1) using a 'Wing' sound has demonstrated that there is no fixed relationship between uterine cavity length and total uterine axial length. The accurate measurement of total uterine axial length unfortunately gives limited information regarding uterine cavity length(l). This measurement is important in relation to intrauterine device research(2). In evaluating the effect of uterine length on the performance of the Copper-7 intrauterine device(3), the investigators suggested that the fundus was not reached during sounding of some of the multiparous patients. They suggested that the sound met resistance before reaching the fundus in some patients with hyper-an~iflexed or retroflexed uteri. This explanation was given for the relatively high incidence of multiparous patients with "short" uteri. These patients had higher intrauterine device event rates than the controls. Accurate determination of uterine axial length in this group of patients may thus be of practical as well as of academic importance. Inadequate sounding may be
364
OCTOBER 1979 VOL. 20 NO. 4
CONTRACEPTION
a factor responsible for the higher event rates including partial expulsion and pregnancy. If the adjustable cervical stop on the inserter tube of the device is placed according to the erroneous soundingTthe device will be sub-optimally placed in the u~erine cavity, i.e. it would not abut against the fundus in those patients whose uterine length had been underestimated. The Mark-7 or similar flexible type of sound should help to avoid this group of patients. Since accurate flexible disposable sounds are not generally available, it is suggested that the inserter tube of the Progestasert device could be used when accurate determination of uterine axial length is required.
ACKNOWLEDGMENTS
I would like to thank Mrs~ Jan Bumstead, Director of the Well Woman Centre, for per~Lission to publish the results of this study and Professor John Newton and Dr. Tony Reading for comment and advice on the manuscript.
OCTOBER 1979 VOL. 20 NO. 4
365
CONTRACEPTION REFERENCES
i.
Hasson, H. M. Differential uterine measurements recorded in vivo. Obstet Cyneeol 43 400-412 (1974)
2.
Hassor H. M., Berger, G. S. and Edelman, D. A. Factors affecting intrauterine contraceptive d~rice performance I. Endometrial cavity length. Am J Obstet Gynecol 126 973-981 (1976)
3.
Gibor, Y., Deysach, L. and Nissen, C. H. Uterine length: a prognostic indicator for the successful use of the Copper 7 intrauterine device. J Reprod Med ii 205-208 (1973)
366
OCTOBER 1979 VOL. 20 NO. 4
THE MARK-7 INTRAUTERINE SOUND - AN ACCURATE DETERMINANT OF UTERINE AXIAL LENGTH
N. D. GOLDSTUCK Marie Stopes House Well Woman Centre 108 Whitfield Street London WIP 6BE, England
ABSTRACT The axial uterine length of 60 nulliparous patients has been measured using a standard Galabin sound and a new flexible disposable sound (Mark-7). In 47 patients the values obtained with the plastic sound were between 0.25 cm to 0.5 cm greater than the values obtained with the metal sound. The flexible plastic sound values are probably larger because this sound is able to follow uterine axial curvature. The element of parallax error which is inherent in using metal sounds is avoided by use of a sliding half-collar at the distal end of the instrument, which can be moved against the cervix allowing fixed measurement. This instrument should be a useful adjunct to intrauterine device research and usage where the relationship of uterine length to device performance is being considered. Correspondence should be addressed to:John Wyeth & Brother Ltd., Wyeth Laboratories, Huntercombe Lane South, Taplow, Maidenhead, Berks, England Accepted for publication September 4, 1979
OCTOBER 1979 VOL 20NO. 4
359
CONTRACEPTION
INTRODUCTION
The clinical determination of uterine axial length is usually by measurement with a Galabin or similar rigid metal sound. The graduated end of the sound is angled at approximately 45 degrees to the horizontal. This type of sound will therefore measure uteri flexed (either forward or backward) at about this angle most accurately. The inaccuracies which arise in the measurement of uteri which are not flexed in the region of this angle probably result from the mismatching of the sound to the uterine axial curvature. The distal tip of the sound thus fails to reach the uterine fundus. The inaccuracy due to this factor is probably fairly small. A further inaccuracy often derives from the operator not being able to read the probed length once the sound has been inserted into the uterus. The presence of blood or sufficient mucus in the cervical canal or on the cervix may help in this regard, if present; alter-natively an estimate of the depth to which the sound has been passed has to be made. This is often erroneous and compounded by the error of parallax. The above inaccuracies are of limited importance in most clinical situations. While initiating a trial of intrauterine device usage in patients with small uterine axial length (<6 cm), it became imperative to make accurate measurements. The difficulties in using standard metal sounds are compounded by the fact that (i) they are usually marked from 6 cm onwards only & (il)the first 4-5 cm of these sounds are curved and therefore unsuitable for making measurements of small uteri which are only slightly or very acutely flexed.
METHODS
Uterine axial length measurement was made using a Galabin sound. This reading was followed hy taking a reading with the ~ k - 7 (G. D. Searle & Co.) sound. This is a sterile packed, disposable, flexible, polypropylene sound, the end of which is ball tipped to avoid causing uterine perforation.
360
OCTOBER 1979 VOL. 20 NO. 4
CONTRACEPTION
The distal end is enclosed by a flanged half-collar whose position can be stabilised by depression after being pushed up against the cervix. Axial uterine length is then read off a scale on the posterior aspect of the sound which is exposed through a window in the half-collar (Figure i). A second method was occasionally used. This is based on the use of the inserter tube of the Progestasert system. The device itself was discarded and the open end of the tube sealed with inert epoxyresin. It was resterilised in O.i per cent benzalkomium chloride for 24 hours. Uterine axial length could be read off the position of the arm-cocker along the graduated stem. This instrument is flexible and incorporates a 25 degree curve, and is thus very suitable for accurate measurements in highly flexed uteri. Care must be taken to allow for the length of the cervical seeking tip of the Progestasert itself, which should be added to the values which are obtained. Nulliparous patients with clinically small uteri were sounded in the usual way. A vulsellum was applied to the anterior lip of the cervix to stabilise the position of the uterus but no downward traction was exerted. Sounding with the metal sound preceded sounding with the Mark-7 sound. This procedure ensured objectivity as the reading obtained with the metal sound was first noted. The subsequent reading which is obtained with the Mark 7 sound cannot be made until the Mark-7 has been inserted, the halfcollar position fixed and the instrument withdrawn from the uterus. As the measurement scale is situated on the posterior aspect of the Mark-7, the reading obtained with the metal sound cannot influence that obtained with the Mark-7. This does not apply to the Progestasert inserter method, as the scale is on the anterior aspect of the tube. Occasionally resounding with the metal sound was performed to ensure that the flexible sound was not breaking down endometrial tissue, e.g. synechiae, etc. On all occasions(ten), the conventional sound gave the same reading before and after the use of the plastic sound. This procedure was therefore abandoned to avoid unnecessary passage of instruments into the uterine cavity. Only patients whose uteri sounded less than 7 em with the Mark-7 were considered eligible for the study.
OCTOBER 1979 VOL. 20 NO. 4
361
CONTRACEPTION
Fig. 1 (from left to right). The posterior aspect of the Mark-7 sound illustrating the ball tipped end (A) and the dual distal (B) and proximal (D) stales. The latter is in black relief and visible through a windew in the half-collar (C), and is the one that is normally used. Two side views of the Mark-7 showing the half-collar in the movable (E) and in ~he depressed fixed position (F). ~The diagram is drawn to scale in the longitudinal direction only).
362
OCTOBER 1979 VOL. 20 NO. 4
CONTRACEPTION
RESULTS
The results obtained from 60 patients are illustrated in Table I. These results indicate that the Galabin sound underestimates uterine axial length by between 0-0.75 cm as compared to the Mark-7 sound. Too few measurements were made with the Progestasert inserter method for a strict comparison with the Galabin sound, but all measurements obtained were equal to or greater than those obtained with the latter, again co~:irming its tendency to underestimate uterine axial _ ngth in the range of 5-7 em. As the Mark-7 scale is graduated to the nearest r only, it is not possible to take readings to an accuracy of less than a quarter of a centimetre. The thirteen readings which were less than this amount different from the aletal sound reading~were biased against the Mark-7. These results, however, remain highly statistically significantly different (Sign test, P
TABLE I MEASUREMENT OF TOTAL UTERINE AXIAL LENGTH IN 60 SUBJECTS
Number of measurements
*Difference in reading between plastic and metal sound (cm)
13
0
41
0.25 - <0.5
6
0.5
- <0..25
0.75
*Readings are determined as plastic sound value minus metal sound value in all cases.
OCTOBER 1979 VOL. 20 NO. 4
363
CONTRACEPTION
DISCUSSION
These measurements have not been compared and correlated with an independent method of measurement, e.g. hysterography. Nevertheless, since the readings with the flexible Mark-7 sound tend to 'over-read' the axial uterine length;it is reasonable to assume that these measurements are closer to the tr~e uterine axial length, as uterine flexion is variable and can be accommodated by the flexible, but not by the metal, sound. The latter will give most accurate readings of axial length at uterine flexion in the range of 40-45 degrees. At this degree of flexion the readings obtained on the two types of sound will presumably be equal, accounting for the observations in Table I. The plastic sound would follow uterine curvature and lover-read' at angles significantly larger or smaller than 40-45 degrees. These results suggest that flexible sounds are more accurate than rigid metal ones insofar as assessing total uterine axial length is concerned, The latter point must be stressed as recent work by Hasson(1) using a 'Wing' sound has demonstrated that there is no fixed relationship between uterine cavity length and total uterine axial length. The accurate measurement of total uterine axial length unfortunately gives limited information regarding uterine cavity length(l). This measurement is important in relation to intrauterine device research(2). In evaluating the effect of uterine length on the performance of the Copper-7 intrauterine device(3), the investigators suggested that the fundus was not reached during sounding of some of the multiparous patients. They suggested that the sound met resistance before reaching the fundus in some patients with hyper-an~iflexed or retroflexed uteri. This explanation was given for the relatively high incidence of multiparous patients with "short" uteri. These patients had higher intrauterine device event rates than the controls. Accurate determination of uterine axial length in this group of patients may thus be of practical as well as of academic importance. Inadequate sounding may be
364
OCTOBER 1979 VOL. 20 NO. 4
CONTRACEPTION
a factor responsible for the higher event rates including partial expulsion and pregnancy. If the adjustable cervical stop on the inserter tube of the device is placed according to the erroneous soundingTthe device will be sub-optimally placed in the u~erine cavity, i.e. it would not abut against the fundus in those patients whose uterine length had been underestimated. The Mark-7 or similar flexible type of sound should help to avoid this group of patients. Since accurate flexible disposable sounds are not generally available, it is suggested that the inserter tube of the Progestasert device could be used when accurate determination of uterine axial length is required.
ACKNOWLEDGMENTS
I would like to thank Mrs~ Jan Bumstead, Director of the Well Woman Centre, for per~Lission to publish the results of this study and Professor John Newton and Dr. Tony Reading for comment and advice on the manuscript.
OCTOBER 1979 VOL. 20 NO. 4
365
CONTRACEPTION REFERENCES
i.
Hasson, H. M. Differential uterine measurements recorded in vivo. Obstet Cyneeol 43 400-412 (1974)
2.
Hassor H. M., Berger, G. S. and Edelman, D. A. Factors affecting intrauterine contraceptive d~rice performance I. Endometrial cavity length. Am J Obstet Gynecol 126 973-981 (1976)
3.
Gibor, Y., Deysach, L. and Nissen, C. H. Uterine length: a prognostic indicator for the successful use of the Copper 7 intrauterine device. J Reprod Med ii 205-208 (1973)
366
OCTOBER 1979 VOL. 20 NO. 4