A method of assessing the level of the head clinically in 'fifths of the head above the pubic symphysis' is described, illustrated, and commented upon. Its value in delineating the descent of the head in problem cases, and as a guide to whether or not the. head can be delivered safely from below, has been proved in thousands of cases presenting with problems of disproportion at King Edward VIII Hospital, Durban. Confirmatory evidence by radiographic examination has been forthcoming in a largepercentage of cases. The traditional methods of assessing the level of thehead, by its 'station' and 'engagement', are described and subjected to criticism. They are theoretically unsound, and practically misleading, especially in problem cases.S. Afr. Med. J . 48, 784 (1974)

Crichton, D

English

AJOL - African Journals Online

7840& G 22S.A. MEDICAL JOURNAL(Supplfment-South African lournal of Obstetrics and Gynaecology)17 April 1974A Reliable Method of Establishing the Level of theFetal Head in ObstetricsD. CRICHTONSUMMARYA method of assessing the level of the head clinically in'fifths of the head above the pubic symphysis' is des-cribed, illustrated, and commented upon. Its value in de-lineating the descent of the head in problem cases, andas a guide to whether or not the. head can be deliveredsafely from below, has been proved in thousands of casespresenting with problems of disproportion at KingEdward VIII Hospital, Durban. Confirmatory evidence byradiographic examination has been forthcoming in a largepercentage of cases.The traditional methods of assessing the level of thehead, by its 'station' and 'engagement', are described andsubjected to criticism. They are theoretically unsound, andpractically misleading, especially in problem cases.S. Afr. Med. l .• 48, 784 (1974).Hitherto only the term 'engagement' or 'station' of thehead has been employed universally to describe and assessthe level of the fetal head in clinical obstetrics. The prac-tical significance, however, of engagement is so nebulousthat an examiner can be guaranteed the following defini-tion if he asks a candidate to define this term in a finalmedical examination. 'When the largest diameter for that"articular presentation has passed through the brim of theoelvis'. Should an examiner ask a candidate to correlatethis definition with the fetal head in its clinical relation-ship to the maternal pelvis, he will find it difficult to do so.The potential dangers in mistaking the level of the headdeserve emphasis and elaboration, and the need to establishuniformity and an accurate method for describing thelevel of the head in the pelvis is the purpose of this article.In pursuance of this, a method of assessing the level ofthe head, the fifths of the head above pubic symphysismethod, is described. This and other established methods(of engagement and station of the head) are subjected to acritical analysis whereby the reliability of each is assessedand each is compared.REQmREMENTS OF ANY METHOD INASSESSING THE LEVEL OF THE HEADThe point selected must be easy to palpate, have obstetricsignificance, and be unchanged by the pressures of difficultDepartment of Gynaecology and Obstetrics, University ofNatal and King Edward VllI Hospital, DumanD. CRICHTO_ , M.B. CH.B., D.PmL., F.R.C.S., F.R.C.O.G.Paper presented at the Interim Congress of the Society of Obstetricians~'1d Grnaecolo~ists held in Port Elizabeth on 23 September 196~.labour on both the fetal head and maternal pelvis. Thesefindings should be easily and reliably carried out by bothmedical and nursing staffs. These being the requirements,they constitute the best yardsticks whereby the merits ofavailable methods of assessing the level of the head canbe evaluated and compared.FIFTHS OF THE HEAD ABOVE THEPUBIC SYMPHYSISThis is defined as that proportion of the head (described infifths) which lies above the level of the pubic symphysis.Thus the head completely above the level of the puoicsymphysis is described as five-fifths above, and the headdeep in the pelvis (with neither sinciput nor occiput pal-pable abdominally) is nought-fifths above. The occiputcan only be just tipped when the head is two-fifths above(engaged). Only the sinciput can be just tipped when ahead is one-fifth above (Fig. 1).Landmarks on the Fetal HeadThese are the occiput and sinciput and, if the head ishigh, the midpoint on an imaginary line is drawn betweenthem. These points are easily defined by different observers.Neither moulding nor caput of the fetal head can preju-dice the accuracy of assessing their level because theylie along the base of the skull.Landmark on the PelvisThis is the upper border of the pubic symphysis. Thelandmark is easily palpable in all cases and can be reliablycarried out by different observers. .Analysis of the ConceptA basovertical diameter' extending from the base of theskull to the most distant point of the vertex measures onlyslightly less than the biparietal diameter which is just over9 cm in an average 3,182-kg baby. Therefore, 2 cm on thisline represents roughly one-fifth of the head.As regards the selection of reliable landmarks on thepelvis, it might be said that the level of the pubic symphysisis not the level of the brim of the pelvis. From a practicalstandpoint, however, the correlation between the levels issufficient to render the level of the pubic symphysis ac-ceptable as all index of the level of the brim, for clinical17 April 1974 S.-A. MEDIESE TYDSKRIF(Byvoegscl-Suid-Afrikaanse Tydskrif vir Obsrerrie en Ginekologie)7850& G 23Sinciput +++++Occiput ++++ ABDOMENSinciput ++Occiput + ItiJ;:~1 Sinciput +tii~1Occiput Nil~......__....,.............._ PUBICSYMPHYSISCAESAREAN SECnON a. Symphysiotomyb. CraniotomyTRIALFORCEPSMIDFORCEPSLOWFORCEPSFig. 1. Level of tbe bead in fiftbs above pubis symphysis.purposes. Theoretically, special allowances could be madein cases with very high or low assimilation pelves, butduring an experience of problems of disproportion noneof my staff have found correction clinically advantageous,even though it would have been easy to do so, for theinterpretation of radiographs taken during trials of labouris undertaken exclusively by the obstetric staff conductingthe trial of labour in our unit. Thus, correlation of theclinical level of the head with the precise level seen onradiographs taken at that time, has been forthcoming ina high percentage of cases.Practical Application of the MethodThe clear definition of the levels of the sinciput andocciput as well as the upper margin of the pubic symphysis,the bladder naturally being empty, is essential. The levelof the upper margin of the pubic symphysis should bemarked with an indelible line.The sinciput and occiput levels are most accuratelydefined by the 'second pelvic grip'. Mistakes are commonwhen the hands are not maintained almost in line with theforearms and when palpation commences too low, tooanterior, and too forcefully, with fingers, as opposed to thegentle pressure with the flat of the hand. The fingers mustbe held almost parallel to the surface of the abdomen,with a little additional pressure being applied at times,by slight flexion of the metacarpophalangeal joints (notinterphalangeal joints) (Fig. 2). There is no force likegentleness for this palpation.Occasionally difficulty is experienced when the occiputlies posterior and when the lower abdomen is prohibitivelyresistant to palpation. A combined abdominovaginalexamination will help to clarify the position, for the fingersin the vagina are able to impart small degrees of move-ment to the sinciput and occiput, which renders theirlevel more easily appreciated by the fingers on theabdomen (Fig. 3). A better appreciation of the size ofthe fetal head is an additional advantage.The levels of the sinciput and occiput can be markedon the anterior abdominal wall, and a line drawn betweenFig. 2. Second pelvic grip--correct positioning of forearms,hands and fingers.them would indicate the degree of flex ion and the level ofthe base of the skull; but special care must be taken notto distort the level of the abdominal skin in marking thesepoints. This practice has proved helpful in teaching and7860& G 24S.A. MEDICAL JOURNAL(Supplemeni-Solllh African Journal of Obstetrics and Gynaecology)17 April 1974THUMB RESTING ONUPPER MARGIN OFPUBIC SYMPHYSIS:--.'-ESTIMATING LEVEL OF THE HEAD BYABDOMINAL-PELVIC EXAMINATIONFig. 3. Abdominopelvic method of assessing head level.checking upon the accuracy achieved by students and staff.It is also helpful as a guide to radiographers undertakingintrapartum radiography, for they are thereby able toavoid omitting part of the head from radiographs.It has recently been suggested' that this method couldbe modified by placing the fingers of the right hand supra-pubically while palpating the sinciput and occiput with aleft-hand reversed Paulic's grip. This method, however, isactually not a modification, but a different method whichwas evaluated some years ago in our Unit and found tooinaccurate to use. The reasons are as follows:Although the reversed Paulic's grip is supposed to besuperimposed on points previously established by thesecond pelvic grip, all too soon the staff lapsed into'establishing' the level of the head with the reversedPaulic's grip, whether a preliminary second pelvic griphad been done or not. Whereas the inaccuracy is notserious when the head is more than three-fifths above, in-accuracy when the head is three-fifths or less above(especially when the occiput is posterior) is often disastrousat levels which have greatest obstetric importance. Further,when it comes to assessing the level of the head as beingone- or two-fifths above, this is assessed with the breadthof I or 2 fingers above the pubic symphysis in the sug-gested modification; but these head levels are well abovethose employed in my method (i.e. sinciput just tipped-one-fifth above, and occiput just tipped-two-fifths above).It will be seen, therefore, that the suggested modificationis actually a different method altogether, and why itsinaccuracy is dangerously misleading.ENGAGEMENT OF THE HEADThe accepted definition of 'engagement' is when the largestdiameter for that particular presentation has passedthrough the brim of the pelvis.Landmark on the HeadIn clinical practice it is impossible to palpate or ascertainprecisely what is the largest diameter for that particularpresentation. Some obstetricians attempt to defend thisimaginary clinical landmark by saying that it can be cor-related with the lowest point of the head palpated vaginallyin relation to the ischial spines. This introduces the dis-advantageous vaginal examinations, and presupposes thatthe head is not elongated by moulding (which it probablywould be in a problem case). The further assumption thatthe distance between the ischial spines and the level of thebrim is constant is also likely to be erroneous in problemcases.Other obstetricians try to relate this indistinct clinicallandmark on the head with the position of the biparietaldiameter (passing through the brim of the pelvis), but this,too, cannot be defined clinically, and the level of the bi-parietal diameter varies considerably in relation to otnercranial diameters, with moulding.17 April 1974 S.-A. MEDIESE TYDSKRIF(Byvoegsel-Suid-Afrikaanse Tydskrif vir Obstetrie en Ginekologie)7870& G 25Landmark on the PelvisThe brim of the pelvis is selected for this measurement.It is impossible to determine the level of the pelvic brimby abdominal palpation. Further, variations in the angleof pelvic inclination and variations in the levels of theavailable conjugate and transverse diameters may lowerthe level of the available brim below the clinical guessesmade when this method is favoured. In practice thediversity of assessments of this plane when engagement isbeing determined is considerable.It follows that the widely recognised fact that differentobservers (nurses or doctors) often give contradictoryestimations of engagement in problem cases should nolonger arouse surprise, but fulfil expectations in the lightof the nebulous nature of landmarks selected on the fetalhead and the maternal pelvis demonstrated in this analysis.Further elaboration is superfluous to prove that the con-cept of engagement of the head constitutes one of thosemeaningless clinical definitions which have been handeddown from textbook to textbook; one which should berelegated to obstetric history!STATION OF THE HEADThe station of the head is the relationship which its lowestcranial point bears to the level of the ischial spines (Fig. 4).Landmark on the BeadIn normal cases with no disproportion, establishment ofthe level of the lowest cranial point is easy. It is the prob-lem case, associated with disproportion in labour, in whichaccurate establishment of the level assumes importance;here it is difficult, unreliable, and misleading. In trials oflabour associated with ruptured membranes and dispropor-tion, an overlying caput succedaneum will give the im-pression that the head is far lower than it really is, andwill obstruct a clear definition of the lowest cranial point.Furthermore, the greater the moulding of the head, themore it elongates (lengthening of the basovertical dia-meter'), thus the lowest point of the cranium descends,whereas its base remains stationary or descends moreslowly (Fig. 4).Consequently, once again the.obstetrician can easily betempted to deliver a head vaginally when its true level isdangerously high, and deluded into the belief that there isprogress in a trial of labour in terms of descent of thehead when this is not so.Landmark on the PelvisThe ischial spines are recognisable on vaginal examina-tion and establish the level of the bispinous diameter.Part of the confidence placed in the selection of thislevel, however, rests upon the assumption that it bears aconstant relationship to the level of the brim which is theMisleading -STATION OF THE HEAD"if Caput and moulding existSTATION OF THE HEADFig. 4. Station of head (top), and moulding and caputdestroying reliability of assessing head level by station(bottom).main obstacle to the descending head. Unfortunately, thisis often an erroneous assumption in problem cases.The assessment of the level of the head in terms ofstation of the head has serious shortcomings; first, theassessment cannot be made abdominally-pelvic examina-tions are essential; secondly, the landmark selected on thefetal cranium becomes incapable of clear definition dueto caput formation, and decreases in reliability propor-tionately to moulding; and thirdly, the pelvic landmark isunreliable in practice.REFERE 'CES1. CrichlOO, D. (1962): J. Obstet. Gyn.ec. Brit. Emp., 69, 366.2. Notelovitz, M. (1973)' S. Afr. J. Obstet. Gyn.ec., 11, 3.

A Reliable Method of Establishing the Level of the Fetal Head in Obstetrics

A method of assessing the level of the head clinically in fifths of the head above the pubic symphysis' is described, illustrated, and commented upon. Its value in delineating the descent of the head in problem cases, and as a guide to whether or not the. head can be delivered safely from below, has been proved in thousands of cases presenting with problems of disproportion at King Edward VIII Hospital, Durban. Confirmatory evidence by radiographic examination has been forthcoming in a large percentage of cases. The traditional methods of assessing the level of the head, by its 'station' and 'engagement', are described and subjected to criticism. They are theoretically unsound, and practically misleading, especially in problem cases.S. Afr. Med. J. 48, 784 (1974)

Crichton, D.

A reliable method of establishing the level of the fetal head in obstetrics

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A Reliable Method of Establishing the Level of the Fetal Head in Obstetrics

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