Fundal height measurement

FUNDAL HEIGHT MEASUREMENT Part 4-Accuracy of Clinicians’ Identification of the Uterine Fundus During Pregnancy*

Janet L. Engstrom, CNM,

PhD,

Barbara L. McFarlin,CNM,

RDMS,

MS,

and

Mile B. Sampson, mD,ms

ABSTRACT The purpase cd IhiS St+ was to detemirta hau accumkly c,,ntctans cd” identify the uppemos, borderof the utelinefunduswhenthq obtainfundalh&t mw~uremp”ts. Clinictanswere inskwted to fdenttfythe uppermostborder of the uterine fundus t” their usualmannerandmakea smallpen markon thr maternalabdomenat that pcZnt Real-timeultmmnogmphywas then usedto locatethe actuallevel of the fundur and measurethe distancebetweenthe cltntctan’raweswent and the actuallevel of the fundur. Measurements were obtatnedfrom 126 women.Six clinicianspatictpakd in the study. and the differences between the cttntctans’ errors were not statM.xlly sig“&a”, IF = 1.26; d.f. = 5,120; P = 28731. Fortbe enwe seties. the mea” emx was -AS cm (SD = 1.99 cm), the mea” absolute emx was 1.25 cm. the maximal error wanS.6an. thepercentageof~rsthatexceededl cmwas42.1%,andthep”taSe of esmnthatexc~eded 2cmwas20.6%. Examtnerenorwasnotarroeiatadwithfactors such as maternal height prepregnacy weight, present v&t, prepregnancy body “lass index. Dadtv. Qestational weeks. the amOUnt of fat 0” the anterior abdominal wall. cHhepr&ceo~& ph~entaorfetalpa~int~~dus. Examinerenorwastnfluenced by thickness of the utedne wall and fetal prerentatto”. These Rndtngr indicate that clinicians makeerrors in identiF,ring the utaino fundus in a sigCftca”t “umber of caw and that the methods used bv cllnlctans to identify the uterine fundus need to be evaluated and imtwxed.

Fundal height meawwmenk am used in many clbical settings to evaluate the appropliattTnes5of utertne StE for the number of gestational weeks. Abnormal fundal height measuremenk can indicate the presence of several serious pqwxy complicationssuch as fetal growth dkhwbances (l-31,

318

multiple gestations (2.4.5). amniotic fluid volume dismders (2. 6). hvdattdiform m&s 171, and el~ors fn esthnattngthe sgtattonal inkwdl. Thus, the ability lo obtain accurate fundal height mea~uremenk is essential for safe clinical practice. Despite the Importanceof accurate fundal height measurements. 5eveml recent shxltes (S-12) of the Intra- and fnte~xmnfner reliability of measurements indicate that clinicfan error fn obtaining these measurements may be large enough to seriously decrease the predictive validity of measure-

_

Jcamaf

d Nwse-hUdwtfen/

.

menh Although clfnically significant differences within and between examinen meas”re”le”k have bee” repoMd, the causes of clfntctanenor in obtaining fundal hetght measure“wnk have not been studied extensively. Only two studies (9. 13) have examined factors that may influence inha- and interexaminer relkbtlity. Seth of these shldies found that neither maternal nnthrapometi factors such as weight for hefght, body nxe index, and &infold thickness, nor obstebic factors such as p&y, g&attonal weeks, and mean fundal height

Vol. 38. No. 6, NavemberlDecembn

1993

measurement significantly influenced examiner error. The only variable significantly associated with interexaminer etmr was abdominal skinfold thickness,and thiseffectwas not consistently present (13). Thus. these studies that maternal anthropomebtc and obstetsiccharacteristics may not be important causes of clinician error. One plausible cause of clinician error is that clinicians may have diffcuky identifying the uppermost border of the uterine fundus accurately. Although the accuracy of clinician a+ wxment of the utedne fundus has not been studiedDWk,“dX one adv (8) did demon&e thai when the fundus was identrfied by ullmsonqraphy for clinicians, the differences within and between examiners’ measurements were remarkably smaller than when the uterine fundus was identffted by palpation. This finding SLIP that inaccurate identification of the uterine fundus may be a source of clinldan error in obtaining fundal height meawrements The purpose of this study was to determine hew accurately clinicians could identfw the uppermost border of the uterine fundus. Ufnicfan enor was assessedby using lea!-time ultmsonqraphy to measure the distance between the clinician’s assessment and the actual level of the uppermost border of the uterine fundus.Asemndqpmposeofthfs~dy was to determine whether maternal, fetal. uterine, and placental factorsinfluenced clinician error.

suggest

terminehow Sample A convenience sample of 126 preg“ant women was selected from women regjstered for prenatal care in the obstemc clinic of a university haspital in a large city in the mid&em United States. The only criteria for sample selectionwere that the uterine fundus was large enough to be palpated through the maternal abdomen and that an ultrasound examination was scheduled for that day. Only women who were already scheduled for an ulhasound examination for medical or obstetric reasons ‘were asked to participate in the study; no ufhavlnogmms were p2lfcmled s&y for the purpose of tbii study. Each woman provided verbal c&sent to paticipate in the study, and this study was approved by the Institutional Review Board of the Urziversitvof Illinois Chikqo. Charataistks df the study samole are described in Table 1. Sl’x clinicians participated in the study: one obstetric resident. three certified nursemidwives, and two student nurse-midwives. The number of wessments performed by each clinician varied from six to 42 and depended on how frequently the ciinician worked in the clinic on the days the researchers were collecting data. Two ulhasonographen participated in the study: one registered ultrasonogmpher and one nurse-midwife trained in the we of ultmsonogmphy.

at

P&r to the onset of data collection, the two ultcasoncgraphe~ worked together and consulted with a son&&t to develop the procedures that would be used to identify and mark the uppemnst border of the uterine fundus and the point identified as the fundus by the clinician, and to measure the distance behwen those iwo

points At the start of data collection. tbe participating clinicians were told that the purpase of the study was to de-

JowMl of Nurse-Mldurdery .

Vol. 38 No. 6, November/December1993

accurately they could identtfy the “ppennc& border of the uterine fundus. Etecaw the purpose of the study was to evaluate the clinicians’ current lewl of accuracyin identifying the uterine fundus, clir.icians were not iWcted or shaun how to idatify the uterine fundus. Ratha, the clinicians were instructed simply to identify the uppermost barder of the uterine fundus in their usual manner and to mark that point with asmallpenmarkpapendtothe midline on the maternal abdomen. An~mwastbaperformed by one of the uknsoncqphers. All ultrasound measurements were performed when tbe uterus was relaxed and with the -n’5 legs extended. The ulbasoncgmpher kid a5QinatI!eedleonthepen~~ by the clinician. The sharp tip of the needle was covered with a rubber erilser.TheThelldba~uas then pbced perpendicular to the needle and the uppemwxt border of the uterine fundus (Figure 1). This needie was used to create a shadow on the ultrasoncgram. Indicating the paint that the clinician had identifted the uppermost border of the uterin0 fundus. This point was marked on the ultmamd screen. Then. the xhlal uppemlast border of the uterine fundus was identified by ultmsonog mphy and marked on the ultrasound screen The image was then frozen, and the distance between these two points was measured using the calp-as on the ultrasound machine. The image was photqmphed and all of the sna~hotr u~eresaved Examples of the vltmsound iv obtained using these procedures are ptided in F&nue 2. In the majority of cd.%, the ultrasonqpam was performed immediately after each &ii tdenti!ied the utertw fundus. Thus, the majority of women did not move and there was rm significant time lapse between the two measwaIents. l-kwever, the warnen examined by hue of the clinf&ms did have :o changerooms and wait briefly fwaffy a few minutes1

as

319

TABLE 1 Charaeteristfcs of the Study Sample fn = 126) n*

Chamctedtic Height (inches) Repregwmcy wetghtIpounds Rerent weight fpaundr) Repngnancy BMIt

Mean

SD

115 62.6 2.93 122 134.7 31.32 124 159.7 34.95 114 24.2 5.43

91 30.7 6.91 Gestational 30.6 6 75 Gesation.1weeksby dates ulssuncgaphy 120 *Datawerenotavailable in al, caws. +Ml = bodymss index.calculated 81 [weight(kgllrihdght(ml12.

between the chIdan’s -t and the uihasonogmm. Because not an measurements were obtained under identical conditions, an analysis of variance was performed to determine whether there were statistically significant differences between the errats made by the dilferent clinicians, The differences behveen cllnidans’ error5 were not stalistically significant fF = 1.26;df. = 5,lZO;P = .28731. All except woof the dinicianrwere blinded to the resultsof tbe ultmsonagram. Both of these clinicians were alsn ml-vestigators, so they were often present during ultmsound -tnations. Tk errors in identifying the

Miwnum 66.0 95.0 107.0 15.8 ::

Maximum 70.0 790.0 300.0 52.3 :;

uterine fundus made by these two Invetigatorj were compared with the errors of those c~inlcianswho were bhded to ukmsound results. A t-test demonstrated that the errors made by the twogroups of examiners were not sl&!kally significant (t = .69, d.f. = 124, P = .4902). Antbropomebic and obstetric dala were obtained from the prenatal record and these data were witten on the back of the photograph. Information from the ultrasonogmm such as gestaUonaI weeks and fetal position and presentation were aim recorded on the back of the photorpaPh

At the completion of data collec. tion, the differences between the cllnicians’ assessmentsand the actual uppermost border of the uterine fundus identified on ukwxogmphy was measured by hand to verify the measurement recorded on the photo. graph that bad been obtained using calipers. If there was a discrepancy between the measurements, an ultrasonographer was asked to decide which measurement was accurate. The photcgraphs were then used to chanxtedstlcsof the mother, uterus, placenta, and fetus to determine whether these factors influenced the accuracy of the clinfclans’ assessmentof ihe uppennoSr border of the uterine fundus. The following characteristicswere assessed: thickness of fat on the maternal antaim abdominal wall; thlcknos of the uterine wall; the presence of the placenta in the uterine fundus; and the preyma of fetal partain the funds. These assessmentswere all performed by an experienced ultrasonow.pher. The following procedures were used to perform these assessments: Tbiclmess of fat an the anterior abdani~l wall. The thicknessof fat on the anterior abdominal wall was measured at two paint% the point at which the uterine fundus was Identified by ukmsonqmphy and the point that the clinician had identified as the fundus. The thicknessof fat was measured with electmcardiqram calipers and compared vith the centimeter scale cm the pho ogmph. 5 ~ftarine waf thickness. Uterine wall thickness was measured with elecimcardt d mm calipers and cornpared with the centimeter scale on thephotograph. Basedo” thesemeasurements, uterine wall thicknesswas classified as thin, medium, or thick.

FIGURE 1 Procedureused to identify the location of the paint identifiedas the utedne tidur by the dintdan. 320

dwmd d Nurse-MidwUw

l

Presence of the placenta or f&f parts in the uterine fuudus. The presenceof the placentaor fetal parts in tbe uterine fundus was determined by visually examining the photowphs. Vol. 3%. No. 6. NwembwDeamtxr

1993

identifieda fetal part 05 the uterine hmdw. RESULTS Data were analyzed using the S&t& tical Analysis System’s P&y, North Carol&i) computer pmgmnl*. Stair tkal analysis was performed using procedures appropriate for descdbing the reliability and valklity of phyical measures (14,lS). A tvpe I enor of 5% was used for all tests of statistkal significance.

The differences between the exam iners’ asseamontsand the acti level of the uterine fundus are summarized in Table 2. An analysis of variance demonstrated that the differencesbe seen individual examiner’s emnx were not statistkaUy significant fF = 1.26: df. = 5.120 P = 2373). Examples of accurate assessmentif

the uterine lundus and the types of errors made In idenU&ing the uterine fundus are provided in Figure 2. Theeffectoffactasuchaspariiy. uterine wall thk!me%, pkcental !Qcation,prwncedfetaipartsinthe fundusqand fetal presentation on examiner error are deskted in Tablo 3. Exammnerormr was not saificanUy inflwxed by p&y ithe

presence of the placenta or fetal parts in the uterine fundus. Examinerenorwas significantly influenced by uterine wall thickness. Examinerenorwas greatestwhen the uterine wall was thin. A posteriori comparisons using a Scheffe prow dure demonstrated that the signiffcant differewes were between the thin and average uterine wedIthicknesses. The compxfsons between the average and ihick uterine walls and the thfn and thick uterine walls were not statlstfcally sfgniffcant Examiner enor was also signiffcantly inffuenced by fetal present+ tion.Examine~emvrwassmnlledwhen the fetus was in a cephalic presenhltion. Ho-, a wsteriori cornpmtsom using a Scheffe procedure did not identify statisticallysignificant differences b&eenthe groups. The cone!ations between examtneremxand maternal characteristics such as height, prepregnancy weight, present weight, prepregnancy body nlass index, gestatfonal weeks Calculated ty dates or by uftmscncqmphy, or the amount of fat on the anterior abdominal wall are pwented in Table 4. None of these conelations were statistically sfgniflcant

TABLE 2 Descrivtiuo of the Examiners’ Ermrs In ldentifvfng the Uterine Fundus

on crni

MD-l CNM-1 CNM-2 CNM-3 SNM-1 SNM-2 Total

126

-0.53

1.31

-0.17 0.38 -1.11 -0.37 0.42

1.01 1.01 2.53 1.30 0.42

-0.45

1.25

1.99

57.9

79.4

TABLE 3 Effect of Parity, Uterine Wall ThIcknew Placental Location. the Presence of Fetal Parts in the Fundus. ad F4al Presentation on Examiner Error Variable

Average Thiik Placentain fundus Yes NO Fetal p=x,In fundur YeS _ No

DISCUSSION Several recent studies (S-12) of the inha- and interexaminer reliability of fundal height measurements indicate that the differences within and between ll?easuIementS may be large enough to seriously decrease the predictive validity of fundal height measurements The causes of these encxs have been studied extensively, but previous studies (9. 13) suggest that maternal anthropometic factors and obstetric characteristics are not important sources of error in fundal he@ht measurement. The findings of this shrdy suggest that dlnlclan error In identifyfng the utedne fundus may be an important source of error in fundal height measurement. In thfs study, clinician error

8.6

-0.04 - 0.53

2.03 1.95

1.24

.2155

- 0.98 0.45 -0.43

1.59 1.43 1.86

3.35

.0387t

- 0.47 -0.42

2.11 1.35

-0.13

-0.47 -0.60

1.68 2.27

0.37

7113

-0.29 -2.17 -3.40 -2.25

1.86 2.57 4.57 3.18

3.11

.034Ll+

.a979

examiners'

322

TABLE 4 Correlations Between Selected Maternal Characterlstfa Examiner Error n

Chomcteristic Height Prepregnancyweight Presentweight Prepregnancybody massindex Gestationa,weeksby dates Gestationalweeksby ultrasonc-graphy Amountof fat at the level of the fundus Amountof fat at the point identifiedas the fundusby the clinician

Jo~lal of Nurse-Mid-

.

115 122 124 114 1;: 126 126

and

r.Ldue .I134 .0154 .0660 - xl298 .0314 -.013a 0333 x942

P-u&e .2077 .8555 .l651 .7532 .7676 .x?% .9705 2940

Vol. 33. No. 6, NovemberiDecember 1993

exceeded 1 cm in 42.1% of the cases, and clinician error exceeded 2 cm in 20.6% of the cases. These findings are worrisome because inaccurate fundal height measurements may cause a clinician to overlook eedous pregnancy complications cx to order unneceseay diagnostic procedures in uncomplicated pregnancies. The number of clinically significant errors observed in this stidy indicate that clinicians must evaluate the pmceduresthat they use to identify the uterine fundus aid do everything possible to impmve the accumcy of their assessm&t of the uppemwzt border of the uterine funda&. Researchers and clinicians need to develop and evaluate methods of impmvin~ the accuracy of clinician identification of the uterine fundus. Future studies should evaluate MTions methods of palpating and percussing the uterine fundus to determine whether these methods improve the accuracy of clinicfans’ identiffcation of the uterine fundus. Additionally, programs of training clinicians to identify the fundus accurately need to be developed and evaluated. The findings of this study indicate that clinkian error was not influenced by factors such es maternal height propregnanq, weight present w@ht, prepregnancy body mass index, parity, gestational weeks, amount of fat on the abdominal wall, OTthe presence of fetal park or the pfacenta in the uterine fundus. Examiner error was influenced by uterine wall tbickness and fetal presentation. which suggeststhat the amount of resistance at the hmdus may be ass&&d w!th clinician encu. The results of this tidy are limited by the investigatori inability to keep ali of the clinicians blinded to the re-

anterior

Jeereel of N,,rse.Midw&,y

.

suitsof the ultrasonogram and by the inabilitv to wrform all of the ultrasonogmms immediately after the clinician examined each subject and to assure that all measurements were done under identical condiions. However, the differences between clinicians’ errors were not statistically significant, which suggeststhat the inability to perform the awments under identical conditions for each clinician did not significantly influence the results of this shldv. Additioonallv. the errors observed in this study are within the range of errors reported in studies of the intm- and interexaminerdifferences reported in otherstudies (S-12). Future studieson thiz topic should attempt to keep all examiners blinded to the wults of ultrasound examinations and to perform all of the ultmsonogmms immediately after the clinician identifies the uppermost border of the uterine fundus.

_ .

-_

REFERENCES 1. Beliin JM. Villas J. Nardln JC, M&mud J. Saim de VicunaI_ Bagnrms of inhauterinegrowth ,etardatio,, by a simoleclinicalmethod: measurementof ufedne height. Am J Obstet Gynecd 1978;131:643-6. 2 Weshn6. G?atidcgmmand fetal wwih ccmpatisonwith biochemicalseper&km. Acta Obstet Gynecol Stand 1977;56:273-82. 3. Quamnta P. CurreU R, Redman CWG. RobinsonJS Predictin of smallfor&es infanttby me7wlrementof symphySial-fend&h&t B, J Obstet GynaecOl19S1;88:115-9. 4. Neilson JP, Verkuyl DA!%. Bannerman C. Taee measurementof svmphysis-f”nda,t&h1 in tin pregnandes. Br J ObstefGynwcol 1988;95:1054-9. 5. Fausun D. Percentageal maternal abdominal length for detectingacceler-

Vd. 38. No. 6. November&cemkr

1993

6. Cab101D. La&man R. M&r J. Uzan Y. sureau c. S?.xenaBE. Treat. mentof pdyhydramnioswith pr&a9bndin synthetaseinhibitor (indometh.acinE. Am J met Gynecol1987:157:422-6. 7. Kohom El. M&., prqnanq,: prezentaiioon and diiwis Clin ObstDtGy. necol 1984:27:181-91.

9. calveli JP. Crean EE. Newor& RG. Pearsa, JF. Antenatalwreening by m?asUementof symphysiF_fundw he&t & Med J 1982:285846-9. 10. BaikySM.SarmandalP,GmntJM A comparisonof three methodsof asseting inter-&eNer “adalio”appkd b memurement of the s,mphuds-fundal height. Br J Obstet dyr&,l 1965; 96~1266-71. 11 Crosby ME, Enworn JL. InterexaminerretiebilL in fendalhemt measurement.MIdwives Chmn Nurs Nota 1989:102:2S&6 12. EngshomJl_ McFadinEL, Sit&r CP. Fur&l b&bt meam,eme,,tpart 2intra-and interexaminer r&&i&J of three measurementtechniques.J Nun0 Mklwifery 19933817-22. 13. En~sixxn J,_ Fundd height and abdominal &“I measurementsduring pre~~lancy[dcctoml diserta~nl. Cbicage:Univ. of IlEnds at Chicago,He&h sciencescenter, 1986. 14. Engmom JL. Asxssmenrof the r&bility of physicalmeasures.ResNun Health 1988:11:3%3-9. 15. Ewtmm Jt Meier PM. Reporting the reliab&y and validityof pbvsical measares. Proceedingofthe 12thAnnual Midva, Nudng Resarch Satiety Conference.wkhii Ksl. 1988: 178.