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Fundal height measurement
FUNDALHEIGHTMEASUREMENT Part 2-Intra-
and Interexarniner
Three Measurement
Reliability of
Techniques
Janet L. Engstrom, CNM, PhD, Barbara L. McFarlin. and Claudia P. Sittler, RN. MS
CNM,
MS,
ABSTRACT The intre- and intefexaminerreliabilityof three fundalheightmeasurementtechniques (two kpe measureand one caliper)wee studiedin a co”ve”ie”cesampleof 60 preg~nt women. The three measuremenkwere obtained twice by hvo examiners Four es aminerswith veylng levelsof dmlcal expertenceparaCipated in the study,one examiner obtainedmeasuremenkin all 60 casesand the other three examinerr each obtained measurements I” approximatelyone-thirdof the casez EMminerswere blindedto their own and to other eMminers’ meeeuwnents. The mea” absolutedifferencesbehueen inditiduel examiner’sfirstand secondmeawemena variedfvnn 0.68 to 1.74 cm, the percentageof dffferences5 1.0 cm varied from 45% to 77.8%. and the maximal differencesvariedfrom 1.6 to 7.5 cm. We calipertechniqueconeistentlydemonrtmkd the smallee.t mea” absoluteinkaexaminerdifferences(0.68 to 1.39 cm) and the highest percentageof intmexeminerdiffenaces L 1.0 cm (55% to 77.8574.The differences b&we” pain of examiners’mear”rer”e”k were contite”ily greaterthan the differ encesbetweenindividualexaminer’smeasurementsi Mean absolutedifferencesvaried from 1.36 to 3.64 cm. the percentageof differencess 1.0 cm varied from 9.1% to 55.6%. and the maxima,differencesvariedfrom 3.1 to 11.5 cm. lnterexaminerdifferenceswere smallestfor the tape “wer-the-cuve” meesuremenkand the caliper“wesweme”k These findingsindicate tha!. to ensuremaximal r&bifi$. fundal height meaeureme”bshould be obrainedby the came cli”iEi” thmughoutpwgra”~y. Addtaoneliy, these findingsindicate that calipe,s may be the most reliable method of obtainingfundal height measuremeti and that the accuracyof calipermeasuremenk i”tde”ti~“gfetalgmwthdishlrbancesandotherpreg~~ycomplica~nsmetitsfunher i~srigetio”.
first
I” the pall of this series of articles on fundal height measuremenk, the various techniques that have been used to rneascre fundal heisht were re&wed and compared. &though many techniquesof measutingfundal height were described, the reliability and validity of the vaious measure-
ment techniques have not been studled adequately to determine whether one technique yields measurements that are more reliable and valid than n,eas”reme”k obkfned with other techniques. Reliability k an essential feature of any fnsbunent used in research or clinical practice (1, 2). Reliahflff k defined as the repeatabilfty, reproducihflfly. a consistency of a measurement, when the measurements
are obtained w&r identical con&tine (1. 2). lntraewmfner relfab4fly k the abttty of one dnician to obtain consistent measurements and interexaminerreliabilityisth+ ability of different clinkk”s to obtain cm&tent measurements. The relkhflfty of the various fun&l hetght nwaswement tDch”iques has not been studied extensively. Thk is problanatk because &able measurements are essential for safe din-
ical prectice. In the absence of reliable measurements, serious pregnancy com&atfons may be owdwked and uncomolkated oreanancies rnev be subjected to ur&&aty diag;ostic orocedures. Thus. it is essenttel that &d&s be conductedto determine the reliability of measurements wed routinely in clinical practice. The purpose of this study is to descdbethe intm and mterexaminerreliability of the three fundal height measurement techniques described in Vamey’s textbook, NurseMidwifery (3). The first technique is a tape measure technique that includes the upper curve of the utedne fundus in the meas”reme”t (tape “over-thecuw”l; the secondtechnique is a tape meawe technique that does not include the upper curve of the uterine fdul. in the measurement@ape“notover-thearve”): and the tit technique is a caliper technique.
REVIEW OF THE UTESATURE Asearly as 1926, Pendleton (4) wrote about the interexaminer reliability of fundal height measurements.He noted that he frequently observed a l-2 cm difference b&wan his own and other examiners’ fundal helqht measurements. However, he did not protide stetisticalevidence to support his obserwdions. The re!iabili$ of fundal height measurements was not mentioned again in the publtshed literature until 1970, when Boa&y and Underhill (5) described interexaminer differ-
18
of five obstehicians’ tape rneasurements of 33 women. The intraexaminer dffferzmr~ avenged 1.6-Z an with a maximal difference of 8.0cm. lrlterexanllner dtfferenc~ were even larger, aver;lging 4.0 cm with a max. imal difference of 13 cm. Calvert et al (11) investigated the intra- and Interexeminer differences of six clinicians’ (obstehidans, restdents, medical students, and midwives1 measurements of 12 women. The standard deviation of the intmexaminer differences was 1.24 cm and the standard devlatlon of the interexaminer differences was 1.72 cm. The Investigators found that the level of training did not significantly Influence the amount of error in the individual clinician’s measurements. Pschera and Soderberq (12) also studied the intra- and int&&niner reliabilib of midwives’ tape rneaeurements oi 10 women. The mean intraexamtner difference for one examiner was 0.4 cm. with a standard deviation of 0.8 cm. The mean interexatiner dtfferencesbetween three examiners’ measurements& from 0.9 to 1.5 cm and the standard deviation varied from 0.7 to 0.9 cm.
ences for tape measure and caliper measurements.They reported that the ,.IC --- I....... ^.. &^i. “l,leiei&U u...“er.. . .._.. _,,” _ . . . . _“,i _.._ ?I technician’s measurements were s1.3cmin&5%ofthecases{n = 50). resardlevj of whether a tama meksur~ or caliper was used to obtain the rnea~urements. However, the actualtechniquesusedtoobtain theceiperandtape roeasurementsu~erenot descrtbed in the study. Crosty and Engstrom (61 also studied the interexaminer differences between four experienced clinicians’ (obstetricians and nurse-midwives) tape measure and c&a measurements of 22 women. The mean dtfference between the four examiners’ tape measuremenb was 3.63 cm, ;vith a maximum difference of 8.0 cm. The mean difference between the caliper measurements was 3.31 cm, witi, a maximum difference of 7.0 cm. O&J 13.6% of the differences betwe& th;? tape measurements were i 2.0 cm, whereas 45.5% of the caltost differences were C 2.0 cm. These investigators suggested tha: c&pen may provide more reliable measurements than tape nleasures. E%aileyet al (7) studied the tnterexaminer differences of two obstettcians’ tape measurements of 39 woman: The mean difference between their mee.wrements was 1.7 cm, with a standard devfation of 1.3 cm The calculated limits of agreement WeYe -5.0 to + 1.6 cm. In a larger series (n = 1,508), Belizan et al (8) studied the interexaminer differences behveen two examine& tape measurements.lhey found a mean difference of only 0.53 cm, with a standard deviation of 0.7 cm. Stmilarly, Rogers and Needham (9) studied the interexamlner differences between obstebtcians’ and either mtdwives’ or nurses’ measurernerds of 265 women. The mean difference was 0.66 cm. with a standard deviationof 1.0 em. Other investigatars have studied both intra- and interexaminer dtffer ences Baggereta (10) described the intra- and interexaminer differences
Journal of NurseMtdwtfery
METHODS Subjects A convenience sample of 60 pregnant women was selected from the private pmctfcee of cerufted nursemidwives and obstemclans. The crtteda for e=mlple set.xtion were that the partiapants were at least 16 weeks’ pregnant and that they agreti to participate In the study.
Examiners Four clinicians with tied levels of clinlcal expertise volunteered to have the reliability of their measurements studied. Three of the clinictans were certified nurse-midwives and one was an&ehi&n.ThefhstcJiManeerved asanexaminerinall60cases, andthe
.
Vol. 38. No. 1, January/February 1993
other three clinicians served as esaminersin22,20, and Idofthecases. rsspactively.Examiners’ years of &Iical experience were as follws: two of the nurse-midwives had six years of experience,one nurse-midtifehad one year of experience, and the obstettcian had eight years of expedence. None of the exarnfners worked together In the swne clinic.4 setting. All participatingdiniciannswereinstructed in the three fundal height measuement techniques by a verbal descrip tion and a clinical demonstration.
Instruments Prior to the onset of data collection, b!ankpaperkpemeasuresweremade fmmp!ainwhite!aminatedpapzr.Bfank tape measures were used to obtain fundal height measuremenk so that examiners would be blinded to their own and to other clinicians’ measurements. Each tape measure was approximately 50.8 x 1.3 cm. A bold, black line was marked approximately 2.5cmfromtheendofeachtapemeawue.Thiismarksetwdastzerorn3rk Eachkpewasmarkedwlththewoman’sstudynumber,examiner’sinitials, measurement technique used, and whether it was the examiner’s first or second measurement. Peltimetycalfperwereusedtoob kinal,[email protected] numeric markings on the caliper were covered with white tape so that axaminers were blinded to their own measurements. The same set oi ca”peerswas used throughout the study. Each caliper meawrement was recorded on a separate index card labeled with the woman’s study nwnher. examhw’sinitials, and whether It was the examiner’s first or second measurement.
Rocedttres Prior to the olwet of data collection, 60 envelopas were sequentially numbered from 1 to 60. Then. the order of examiners (Le.. which examiner would obtain measurements ffmt for
Jo,,r,ml
of Nurs~Mkkutkry .
each set of measuremenk~ was determined using a table of random numbers and ias recorded on each subfeds data cenvekve. The blank bpe measures rmd index cards for each subject were then placed in the corresponding envelopes. Women who met the criteria for sample selection were given a verbal dewdption of the study and asked to participate. After written consent for study participation was obtained. demographic, obstetric, and anthropometric data were rebieved from the woman’s prenatal record Fwda! height measureme”k were obtained, in successWn. usingthe three measurement techniaues. Each measurement was obtained twice by two differentexaminers.Thefundalheiqht measuremenk were obtained ufrgthe fdlowingprocedtues: The woman was placedonanexaminationkbleinasupinepmi&xwithherkgsex3en&dam3 her arms placed at her sidesor xr~s her chest AU measurements were obtained behueen uterine co”tractio”s, and both of the e&s hands were remcwdfmmtheutetusbehveeneach measurement. The tape measuremenk were obtatnedusingthe appropdatelylabeled tape measures.Forboth tape measure techniques, the exz~minemmeasured from the uppemrost border of the symphysis pubis to the uppermost border of the uterine fundus, in the midlineofthematemalabdomen.for thefirstiape-rment,thetaRew inmmp~econtaftwiulue~“~f~e maternal abdomen throughout the fengfh of the measurement For the second tape measurement, the tape was in contact with the skfn of the maternal abdomen lInti the cuve of the uterine fundus was reached. At that point, the tape was extended In a strafghtline from the fundus to the index&d middle ftngers of the examineG.fefthand.whichhbeen~ perpendicular to bardor of the utedne fundus. The exarninerindfcated hisor her measurement onthetapemeznwewlthapenmark at the appropdate point After each
the“ppammt
Vd. 33, No. 1. Janu&F&ruary
1993
measurement, the examh-ter handed thetapemwsuretotkottwrw.alniwrwhofofdedttwtthout!ookingdcingzlniS andwhothznpfxxdthetapemeawe i”theWanan’SmvOlope. Caliper measurements were obtafned with an unmarked pelvimeby c&w.Each-measuredfrom theupperm&bofdeTofthesymphysk pubis to the uppermost bo&r of the uterine fundus in the midline of the maternal ab&men. The examinerusedthesetnewonthecalipertostabt6zetheca6perattheap propdate point and then camfully handed the calfper to the other examiner. Thtt examiner measured the di$tUKebenweniheh~ommtpoinb dthebmnchesofthecaliperbyholding the insbument *nst a long flat ruler that was marked in m3fmeters. i-he mea%lretltent was recorded on 2~1index card and the index card was placed in the envelope. Each examiner obaiwd the three Whet?3htmeanuementsandthell each examiner obtained a second set of the three measurements. The measwemenk were obtained in the same otiforeachwoman. OtxeaUoI the measurements had been &Imined, an of the data coflecwn mated&wrep!acedinthedcofJw tionenvekwandtheerwetwe~
s&2ckbadbeencomp4et~.
when data cGlkcth was cmpkted for all 60 women, the strips of paperusedastapemeawreswere measured by comparing them to a Rat metal rider marked in mitffmetets. Each tape measure was measured
tween the two meaxwmenk was greater than 1 mm. then the measurement was repeated a third time.
uslng
Data were athe St&kiml Analysis System Gay, NC) compuer programs. The data were analyzed using stawjcal procedures
19
TABLE 1 Dtlfe~ences Between Individual Examiner’s Fundal Height Measurements (in cm) Mea.urrment
.a
Tape “over-thesuwe” Examiner A 60 Exasminer B 20 ExaminerC 20 ExaminerD 18 A”eWet
%elcm
_ 5%* 2 cm
MAD
SD
T&U
MAX
1.22 0.82 1.50 0.59
1.53 1.07 1.89 1.24
1.07 0 74 133 0.87
3.6 2.9 3.3 2.7
50.0 70.0 45.0 556
80.0 95.0 70.0 94.4
7.5
0.93 1.68 1.75 1.36
01.18 72 155 0.97
2.0 4.8 3.4
58.3 600 50.0 50.0
88.3 100.0 60.0 88.9
1.20 0.86 1.89 0.84
0.90 0.60 1.32 0.69
4.5 1.6 5.0 1.6
72.9 75.0 55.0 77.8
88.1 100.0 80.0 loo.0
1.13
Tape “not-over-the-curve“ &zz : Examinerc ExaminerD
60 20 20 18
Average Caliper ExaminerA ExaminerB ExaminerC ExaminerD AVerWe
0.84 1.16 1.74 1.11 1.21
59 20 20 18
0.89 0.68 1.39 0.70 0.W
appropriate for describing the reliability of physical measures such as fundal height (1, 13). The statistics that should be presented in this type of study are: the mean absolute value of tl ;e differences between measurestandard deviation of the net differences; thd technical error of measurement, the percentage of differences less than or equal to 1 cm; and the percentage of differences less than or equal to 2 cm (I, 13). Correlation Coefficients Were not caicul&d because this statisticshould not be used to describe the reliabiliiu of physical measures (1, 7, 14). .
RESULT8
five (8.390.) were black, and hv” l3.3%1 were Asian. Twenty-eight (46.7%) of the women were nulllparow. 18 (30%) were para 1. 10 (16.7%) were pam 2, and four (6.7%) were pare 3. Gestational weeks at the time of measurement varied from 16 to 42 weeks. with a mean of 29.8 weeks (SD = 7.0). Maternal height was recorded in 57 cases and varied from 59.5 to 71 inches, with a mean of 64 inches (SD = 2.91). Prepregnancy weight wds recorded in 57 cases and varied from 98 to 277 pounds. with a mean of 131.5 pounds (SD = 30.56). Maternal weight at the time of measurement varied from 117.5 to 295 pounds, with a mean of 157.2 pounds (SD = 33.44).
Demographic. obsteti: and anthropametric characteristics of the study sample are as follows. Fifty-three (88.3%) of the subjects were white,
The differences between individual examiner’s first and second measure-
-=“+z the
7.0
htraexaminer
Reliability
ments are described In Table 1. The mean absolute differencesvaried from a low of 0.68 cm for examiner B’s caliper measurementsto a high of 1.74 cm for examiner C’s tape “not-ovathe-curve” measurements. The largest difference observed was 7.5 cm for examiner A’s tape “not-over-thecurw” measurement. Comoarison of the four examiners demon&ted that examiner B had the smallest mean absolute differences for all three measurement techniques. Comparison of the three measurement techniques demonstrated that the mean absolute differences for all four examiners were smallest for the caliper technique.
Interexaminer
Differences
The differences between pairs of examiners’ measurements~ are desaibed in Table 2. The mean absolute differences varied from a low of 1.36 for examiner A’s and examiner D’s tape “not-over-the-curve” measurements to a high of 3.60 for examiner A’s and examiner B’s tape “not-over-the-cunre”mearurements. The larwt maximal difference was 11.5 cm for examiner A’s and examinor C’s tape “over-the-curve” rneas”reme”ts.
Comparison of pairs of examiners demonstrated that examiner A and examiner D tended to have the smallest mean absolute differences. Comparison of the three measurement techniques demonstrated that tzye “over-the-curve” and the callper techniques had the smallest differences.
DISCUSSION These findings indicate that fundal height measurements are more reliable when they are obtained by the sane clinician than when they are obtained by different clinicians. Previous investigator have also reported that lntraexaminer differences are smaller than interexamIner differences (10-121. Thus, these studies
supporttherecommendation that the same cllnlcian should obtain fundal height measurements on the same u.ornanthroughoutpreg”a”cy (3.15). These Andings also suggest that caliper measurements may be more reliable than measurements obtained with a tape measure. Of the two previous studies that compared the reliability of calipers to tape rneawres. one study (6) found that the differences in caliper measurements were smaller than the differences between tape measurements. However, the other study (5) found that the two methods were not remarkablv different. Thus, the merits of using a caliper rather than a tape rneanxe need to be evaluated further. Although some textbooks imply that caliper mea s”rerrle”ts are superior to tape measurements 13). there are no published studies that have demonstrated that caliper measurements are more accur&e than tape measures in assessirw fetal size or in identttins other pr&nancy complications. theuse of calipers clinically would ako present problems such as the cost of the instrument and issues related to how the instrument is cleaned between patients. Studies comparing the predictive accuracy of calipers and tape measures must be conducted before the use of calipers is recommended in clinical praactice. Regardlw of which technique is used to measure fundal height. the magnitude of differences within and between examiners observed i- this and In other stud&s (6, 7. 101 1sof concern. Because of the amount of measurement error, clinicians should do everything possible to improve the reliability of their measurements. Specific suggestionsfor improving the reliability of fundal height measurements k&de the following: 1. Clinicians should have wrttten protocok that explicitly describe how fundal height should be measured, and all clinicians in that setting must agree upon and use the recommended technique.
TABLE 2
Meescremenr
ond Examiner Pair
n*
MALI
Tape “over-the-curve” Exaai~ A and ExaminerB 22 2 19 1.44 1.73 Set 2 20 1.82 ExaminerA and Examinerc Set 1 20 256 3.40 2.64 Set2 20 2.51 ExammerA and ExammerD 1.14 Set 1 18 1.40 set2 18 1.86 201 *wrage+
1.79 1.69
4.5
57
27.3 35.0
59.1 65.0
2.58 2.27
L1.5 9.1
300 20.0
60.0 55.0
1.20 1.58
z.:
33.9 27.8
72.2 50.0
2.79 2.47
6.2 7.2
9.1 15.0
13.6 35.0
2.62 2.36
7.3 8.8
lC.0 400
30.0 55.0
1.26 128
4.3 3.3
55.6 33.9
72.2 66.7
2.69 2.59
2.37 2.40
7.5 6.9
18.2 15.0
45.5 25.0
3 11 176
2.26 I.45
7.0 4.8
15.0 55.0
55.0 70.0
1.74 1.66
1.23 1.35
4.6 4.0
44.4 47.1
77.0 76.5
206
Tape “not-the-overxurw” Ex∋er A and ExaminerB 22 3.60 1.65 1.95 Set 2 20 2.93 ExaminerA and ExaminerC 2.97 Set 1 20 3.22 337 set2 20 2.40 ExaminerA and ExaminerD 1.58 set 1 18 136 1.64 Set 2 18 1.61 AVemge
2.50
Caliper Examiner A and ExaminerB
set 1 22 2.77 Set 2 20 3.05 Exx,$er A and20 Examiner 258 C set2
20
1.52
Exaai;“’ A and18 Examiner 1.37 D set2 17 152 Average
2.14
2. Clinicians need to identify the landmarksusedinthemeasuringpmcess carefully to make sure that they have accurate!y identified the landmarks. This means that the woman’s abdomen and pubic area must be sutftciently exposed to allow the dnician to identify the lzdmark and place the tape measure without hav-
ing to stntggle with pulling back or holding up the wman’s cbthing. 3. The notion that fundal height should be measured mare than once on the smne woman at each prenatal visit merits consideration. G&I the am-auntof error in fundal hetght meawrem&sobsetwdtntandinoUwzr studies, accuracy of measurements
may be Increased if the measurements are obtained more than once. The findings from this study indicate that some clinicians and pairs of clinicians have smaller differences. AddMonaUy, other investigators (f&9, 121 have reDotied smaller differencxa within and between clinicians’ measurements. Thus, thse findings sugg&that the in&r- and interexaminer reliabiity of fundal height measurements can be improved. It 1sImperative that clinicians and researchen investigate methods of improving the reliability of fundal height measurement&
merits. Future studies must evaluate the reliablllty and validity of the various fundal height meawrement techniques, particularly the caliper technique because preliminary studies indicate that measurements obtained with calipers may be more reliable than those obtained with tape measures. Such studies will allow clinicians to choose the most reliable and valid method of measuring fundal height.
22
8. Beliian JM. Villar J. Nardin JC, M&mud J, Salnr de Vkuna L. Dk.gm,ds of lntmuteline growth retardation by a simple clinical method: nleasurelne”tof uterine height. Am J Obstet Gynecol 1978;131:64&5. 9. RogersMS, Needham PG. Evaluation of fundal height measurementin antenatal care. Aust N Z J Obstet Gynaecol 1985;25:87-90. 10. Baw W, EriksenPS. SecherNJ, ThistedJ. WestergaardL. The precision and accuracyof symphysis-fundusdistance mearurementsduring pregnancy. ActaObstetGunecolScand1985:64:3714.
SUMMARY Because the notdity of foodal height measurementsis determined by evaluating the indiidual woman’s pattern of fundal growth and by comparing fundal height measurements to established limits of nom-ml, reliibiitv within and between clinicians is essential for safe clinical practice. In the absence of intm and interexaminer r&ability. pregnancy complications may be overlooked and uncomplicated pregnancies may be subjected to unnecessay diagnostic procedures. The results of this and other studies indicate that the dlfferences within and behveen clinicians’ measurements are greater than what would be considered acceptable for safe clinical practice. Thus. clinicians must do everything possible to improve the rellabilliy of their measure-
7. B&au SM. SamwndalP. GrantJM. A cornpa& oi three methbds of assessing inter-obsewer variation applkd to measurementof the symphyris-fun&l heiqht. Br J Obstet Gvnaecol 1989: 96126&71.
REFERENCES 1. EngstromJL. Assessmentof the reliabilityof $-~ysicalmeasures.F&sNurs Health 1988;11:3B%9. 2. Potit DF. Hun&r BP. Nursingresearch:pdndpies a4 methods.Brded. Philadelphia:Liwincott. 1987. 3. &mey H. Nurse-midwtfey. 2nd ed. Boston.Bk&well ScientificF’ublkrlion& 1937. 4. PendletonGF. A studyof the contour abdominal of pregnancy. Am J Obetet Gwecol 1926: 12:3’%-414.
measuremnt
5. Be-&y JM, Underhill R4. Fallacy of the fundal height. BMJ 1970;4:40& 6. 6. Crosby ME, En&mm JL Interexaminerreliabilityin fundal heightmeasurement. Mldwtver Chron Nws Note 1989;102%?-6.
Joumat of Nurse-Midwifery .
11. Calvert JP, Crean EE, Newcombe RG, PearsonJF. Antenatalsmeeningby measurement of qmphykhmdw tresht BMJ 1982;285:B4&9. 12. Pxhem H. Sod&erg G. Es& mationof fetalweightby al&minal measurements. Acta ObstetGynecol Sand 1984;63:175-9.
external
13. EngstromJL. Fundal height and abdominal @th measurementsdting weg”ancy [d&oral dksetitationl. Chic?@: univ. of tuirmisat Chit, 1985. 14. Bland JM, Alhnan DG. Sta!kkal methods fw assessingagreement between two methodsof dintcal measurement Lancet 1986;1:307-10. 1.5. Adams CJ. Prognany. In: Adams CJ, editor. Nurse-midwifery:health care for women and newborns. New York: Grune & Skatton, 1983.
Vol. 38. No. 1. JanuarylFebruw 1593
and Interexarniner
Three Measurement
Reliability of
Techniques
Janet L. Engstrom, CNM, PhD, Barbara L. McFarlin. and Claudia P. Sittler, RN. MS
CNM,
MS,
ABSTRACT The intre- and intefexaminerreliabilityof three fundalheightmeasurementtechniques (two kpe measureand one caliper)wee studiedin a co”ve”ie”cesampleof 60 preg~nt women. The three measuremenkwere obtained twice by hvo examiners Four es aminerswith veylng levelsof dmlcal expertenceparaCipated in the study,one examiner obtainedmeasuremenkin all 60 casesand the other three examinerr each obtained measurements I” approximatelyone-thirdof the casez EMminerswere blindedto their own and to other eMminers’ meeeuwnents. The mea” absolutedifferencesbehueen inditiduel examiner’sfirstand secondmeawemena variedfvnn 0.68 to 1.74 cm, the percentageof dffferences5 1.0 cm varied from 45% to 77.8%. and the maximal differencesvariedfrom 1.6 to 7.5 cm. We calipertechniqueconeistentlydemonrtmkd the smallee.t mea” absoluteinkaexaminerdifferences(0.68 to 1.39 cm) and the highest percentageof intmexeminerdiffenaces L 1.0 cm (55% to 77.8574.The differences b&we” pain of examiners’mear”rer”e”k were contite”ily greaterthan the differ encesbetweenindividualexaminer’smeasurementsi Mean absolutedifferencesvaried from 1.36 to 3.64 cm. the percentageof differencess 1.0 cm varied from 9.1% to 55.6%. and the maxima,differencesvariedfrom 3.1 to 11.5 cm. lnterexaminerdifferenceswere smallestfor the tape “wer-the-cuve” meesuremenkand the caliper“wesweme”k These findingsindicate tha!. to ensuremaximal r&bifi$. fundal height meaeureme”bshould be obrainedby the came cli”iEi” thmughoutpwgra”~y. Addtaoneliy, these findingsindicate that calipe,s may be the most reliable method of obtainingfundal height measuremeti and that the accuracyof calipermeasuremenk i”tde”ti~“gfetalgmwthdishlrbancesandotherpreg~~ycomplica~nsmetitsfunher i~srigetio”.
first
I” the pall of this series of articles on fundal height measuremenk, the various techniques that have been used to rneascre fundal heisht were re&wed and compared. &though many techniquesof measutingfundal height were described, the reliability and validity of the vaious measure-
ment techniques have not been studled adequately to determine whether one technique yields measurements that are more reliable and valid than n,eas”reme”k obkfned with other techniques. Reliability k an essential feature of any fnsbunent used in research or clinical practice (1, 2). Reliahflff k defined as the repeatabilfty, reproducihflfly. a consistency of a measurement, when the measurements
are obtained w&r identical con&tine (1. 2). lntraewmfner relfab4fly k the abttty of one dnician to obtain consistent measurements and interexaminerreliabilityisth+ ability of different clinkk”s to obtain cm&tent measurements. The relkhflfty of the various fun&l hetght nwaswement tDch”iques has not been studied extensively. Thk is problanatk because &able measurements are essential for safe din-
ical prectice. In the absence of reliable measurements, serious pregnancy com&atfons may be owdwked and uncomolkated oreanancies rnev be subjected to ur&&aty diag;ostic orocedures. Thus. it is essenttel that &d&s be conductedto determine the reliability of measurements wed routinely in clinical practice. The purpose of this study is to descdbethe intm and mterexaminerreliability of the three fundal height measurement techniques described in Vamey’s textbook, NurseMidwifery (3). The first technique is a tape measure technique that includes the upper curve of the utedne fundus in the meas”reme”t (tape “over-thecuw”l; the secondtechnique is a tape meawe technique that does not include the upper curve of the uterine fdul. in the measurement@ape“notover-thearve”): and the tit technique is a caliper technique.
REVIEW OF THE UTESATURE Asearly as 1926, Pendleton (4) wrote about the interexaminer reliability of fundal height measurements.He noted that he frequently observed a l-2 cm difference b&wan his own and other examiners’ fundal helqht measurements. However, he did not protide stetisticalevidence to support his obserwdions. The re!iabili$ of fundal height measurements was not mentioned again in the publtshed literature until 1970, when Boa&y and Underhill (5) described interexaminer differ-
18
of five obstehicians’ tape rneasurements of 33 women. The intraexaminer dffferzmr~ avenged 1.6-Z an with a maximal difference of 8.0cm. lrlterexanllner dtfferenc~ were even larger, aver;lging 4.0 cm with a max. imal difference of 13 cm. Calvert et al (11) investigated the intra- and Interexeminer differences of six clinicians’ (obstehidans, restdents, medical students, and midwives1 measurements of 12 women. The standard deviation of the intmexaminer differences was 1.24 cm and the standard devlatlon of the interexaminer differences was 1.72 cm. The Investigators found that the level of training did not significantly Influence the amount of error in the individual clinician’s measurements. Pschera and Soderberq (12) also studied the intra- and int&&niner reliabilib of midwives’ tape rneaeurements oi 10 women. The mean intraexamtner difference for one examiner was 0.4 cm. with a standard deviation of 0.8 cm. The mean interexatiner dtfferencesbetween three examiners’ measurements& from 0.9 to 1.5 cm and the standard deviation varied from 0.7 to 0.9 cm.
ences for tape measure and caliper measurements.They reported that the ,.IC --- I....... ^.. &^i. “l,leiei&U u...“er.. . .._.. _,,” _ . . . . _“,i _.._ ?I technician’s measurements were s1.3cmin&5%ofthecases{n = 50). resardlevj of whether a tama meksur~ or caliper was used to obtain the rnea~urements. However, the actualtechniquesusedtoobtain theceiperandtape roeasurementsu~erenot descrtbed in the study. Crosty and Engstrom (61 also studied the interexaminer differences between four experienced clinicians’ (obstetricians and nurse-midwives) tape measure and c&a measurements of 22 women. The mean dtfference between the four examiners’ tape measuremenb was 3.63 cm, ;vith a maximum difference of 8.0 cm. The mean difference between the caliper measurements was 3.31 cm, witi, a maximum difference of 7.0 cm. O&J 13.6% of the differences betwe& th;? tape measurements were i 2.0 cm, whereas 45.5% of the caltost differences were C 2.0 cm. These investigators suggested tha: c&pen may provide more reliable measurements than tape nleasures. E%aileyet al (7) studied the tnterexaminer differences of two obstettcians’ tape measurements of 39 woman: The mean difference between their mee.wrements was 1.7 cm, with a standard devfation of 1.3 cm The calculated limits of agreement WeYe -5.0 to + 1.6 cm. In a larger series (n = 1,508), Belizan et al (8) studied the interexaminer differences behveen two examine& tape measurements.lhey found a mean difference of only 0.53 cm, with a standard deviation of 0.7 cm. Stmilarly, Rogers and Needham (9) studied the interexamlner differences between obstebtcians’ and either mtdwives’ or nurses’ measurernerds of 265 women. The mean difference was 0.66 cm. with a standard deviationof 1.0 em. Other investigatars have studied both intra- and interexaminer dtffer ences Baggereta (10) described the intra- and interexaminer differences
Journal of NurseMtdwtfery
METHODS Subjects A convenience sample of 60 pregnant women was selected from the private pmctfcee of cerufted nursemidwives and obstemclans. The crtteda for e=mlple set.xtion were that the partiapants were at least 16 weeks’ pregnant and that they agreti to participate In the study.
Examiners Four clinicians with tied levels of clinlcal expertise volunteered to have the reliability of their measurements studied. Three of the clinictans were certified nurse-midwives and one was an&ehi&n.ThefhstcJiManeerved asanexaminerinall60cases, andthe
.
Vol. 38. No. 1, January/February 1993
other three clinicians served as esaminersin22,20, and Idofthecases. rsspactively.Examiners’ years of &Iical experience were as follws: two of the nurse-midwives had six years of experience,one nurse-midtifehad one year of experience, and the obstettcian had eight years of expedence. None of the exarnfners worked together In the swne clinic.4 setting. All participatingdiniciannswereinstructed in the three fundal height measuement techniques by a verbal descrip tion and a clinical demonstration.
Instruments Prior to the onset of data collection, b!ankpaperkpemeasuresweremade fmmp!ainwhite!aminatedpapzr.Bfank tape measures were used to obtain fundal height measuremenk so that examiners would be blinded to their own and to other clinicians’ measurements. Each tape measure was approximately 50.8 x 1.3 cm. A bold, black line was marked approximately 2.5cmfromtheendofeachtapemeawue.Thiismarksetwdastzerorn3rk Eachkpewasmarkedwlththewoman’sstudynumber,examiner’sinitials, measurement technique used, and whether it was the examiner’s first or second measurement. Peltimetycalfperwereusedtoob kinal,[email protected] numeric markings on the caliper were covered with white tape so that axaminers were blinded to their own measurements. The same set oi ca”peerswas used throughout the study. Each caliper meawrement was recorded on a separate index card labeled with the woman’s study nwnher. examhw’sinitials, and whether It was the examiner’s first or second measurement.
Rocedttres Prior to the olwet of data collection, 60 envelopas were sequentially numbered from 1 to 60. Then. the order of examiners (Le.. which examiner would obtain measurements ffmt for
Jo,,r,ml
of Nurs~Mkkutkry .
each set of measuremenk~ was determined using a table of random numbers and ias recorded on each subfeds data cenvekve. The blank bpe measures rmd index cards for each subject were then placed in the corresponding envelopes. Women who met the criteria for sample selection were given a verbal dewdption of the study and asked to participate. After written consent for study participation was obtained. demographic, obstetric, and anthropometric data were rebieved from the woman’s prenatal record Fwda! height measureme”k were obtained, in successWn. usingthe three measurement techniaues. Each measurement was obtained twice by two differentexaminers.Thefundalheiqht measuremenk were obtained ufrgthe fdlowingprocedtues: The woman was placedonanexaminationkbleinasupinepmi&xwithherkgsex3en&dam3 her arms placed at her sidesor xr~s her chest AU measurements were obtained behueen uterine co”tractio”s, and both of the e&s hands were remcwdfmmtheutetusbehveeneach measurement. The tape measuremenk were obtatnedusingthe appropdatelylabeled tape measures.Forboth tape measure techniques, the exz~minemmeasured from the uppemrost border of the symphysis pubis to the uppermost border of the uterine fundus, in the midlineofthematemalabdomen.for thefirstiape-rment,thetaRew inmmp~econtaftwiulue~“~f~e maternal abdomen throughout the fengfh of the measurement For the second tape measurement, the tape was in contact with the skfn of the maternal abdomen lInti the cuve of the uterine fundus was reached. At that point, the tape was extended In a strafghtline from the fundus to the index&d middle ftngers of the examineG.fefthand.whichhbeen~ perpendicular to bardor of the utedne fundus. The exarninerindfcated hisor her measurement onthetapemeznwewlthapenmark at the appropdate point After each
the“ppammt
Vd. 33, No. 1. Janu&F&ruary
1993
measurement, the examh-ter handed thetapemwsuretotkottwrw.alniwrwhofofdedttwtthout!ookingdcingzlniS andwhothznpfxxdthetapemeawe i”theWanan’SmvOlope. Caliper measurements were obtafned with an unmarked pelvimeby c&w.Each-measuredfrom theupperm&bofdeTofthesymphysk pubis to the uppermost bo&r of the uterine fundus in the midline of the maternal ab&men. The examinerusedthesetnewonthecalipertostabt6zetheca6perattheap propdate point and then camfully handed the calfper to the other examiner. Thtt examiner measured the di$tUKebenweniheh~ommtpoinb dthebmnchesofthecaliperbyholding the insbument *nst a long flat ruler that was marked in m3fmeters. i-he mea%lretltent was recorded on 2~1index card and the index card was placed in the envelope. Each examiner obaiwd the three Whet?3htmeanuementsandthell each examiner obtained a second set of the three measurements. The measwemenk were obtained in the same otiforeachwoman. OtxeaUoI the measurements had been &Imined, an of the data coflecwn mated&wrep!acedinthedcofJw tionenvekwandtheerwetwe~
s&2ckbadbeencomp4et~.
when data cGlkcth was cmpkted for all 60 women, the strips of paperusedastapemeawreswere measured by comparing them to a Rat metal rider marked in mitffmetets. Each tape measure was measured
tween the two meaxwmenk was greater than 1 mm. then the measurement was repeated a third time.
uslng
Data were athe St&kiml Analysis System Gay, NC) compuer programs. The data were analyzed using stawjcal procedures
19
TABLE 1 Dtlfe~ences Between Individual Examiner’s Fundal Height Measurements (in cm) Mea.urrment
.a
Tape “over-thesuwe” Examiner A 60 Exasminer B 20 ExaminerC 20 ExaminerD 18 A”eWet
%elcm
_ 5%* 2 cm
MAD
SD
T&U
MAX
1.22 0.82 1.50 0.59
1.53 1.07 1.89 1.24
1.07 0 74 133 0.87
3.6 2.9 3.3 2.7
50.0 70.0 45.0 556
80.0 95.0 70.0 94.4
7.5
0.93 1.68 1.75 1.36
01.18 72 155 0.97
2.0 4.8 3.4
58.3 600 50.0 50.0
88.3 100.0 60.0 88.9
1.20 0.86 1.89 0.84
0.90 0.60 1.32 0.69
4.5 1.6 5.0 1.6
72.9 75.0 55.0 77.8
88.1 100.0 80.0 loo.0
1.13
Tape “not-over-the-curve“ &zz : Examinerc ExaminerD
60 20 20 18
Average Caliper ExaminerA ExaminerB ExaminerC ExaminerD AVerWe
0.84 1.16 1.74 1.11 1.21
59 20 20 18
0.89 0.68 1.39 0.70 0.W
appropriate for describing the reliability of physical measures such as fundal height (1, 13). The statistics that should be presented in this type of study are: the mean absolute value of tl ;e differences between measurestandard deviation of the net differences; thd technical error of measurement, the percentage of differences less than or equal to 1 cm; and the percentage of differences less than or equal to 2 cm (I, 13). Correlation Coefficients Were not caicul&d because this statisticshould not be used to describe the reliabiliiu of physical measures (1, 7, 14). .
RESULT8
five (8.390.) were black, and hv” l3.3%1 were Asian. Twenty-eight (46.7%) of the women were nulllparow. 18 (30%) were para 1. 10 (16.7%) were pam 2, and four (6.7%) were pare 3. Gestational weeks at the time of measurement varied from 16 to 42 weeks. with a mean of 29.8 weeks (SD = 7.0). Maternal height was recorded in 57 cases and varied from 59.5 to 71 inches, with a mean of 64 inches (SD = 2.91). Prepregnancy weight wds recorded in 57 cases and varied from 98 to 277 pounds. with a mean of 131.5 pounds (SD = 30.56). Maternal weight at the time of measurement varied from 117.5 to 295 pounds, with a mean of 157.2 pounds (SD = 33.44).
Demographic. obsteti: and anthropametric characteristics of the study sample are as follows. Fifty-three (88.3%) of the subjects were white,
The differences between individual examiner’s first and second measure-
-=“+z the
7.0
htraexaminer
Reliability
ments are described In Table 1. The mean absolute differencesvaried from a low of 0.68 cm for examiner B’s caliper measurementsto a high of 1.74 cm for examiner C’s tape “not-ovathe-curve” measurements. The largest difference observed was 7.5 cm for examiner A’s tape “not-over-thecurw” measurement. Comoarison of the four examiners demon&ted that examiner B had the smallest mean absolute differences for all three measurement techniques. Comparison of the three measurement techniques demonstrated that the mean absolute differences for all four examiners were smallest for the caliper technique.
Interexaminer
Differences
The differences between pairs of examiners’ measurements~ are desaibed in Table 2. The mean absolute differences varied from a low of 1.36 for examiner A’s and examiner D’s tape “not-over-the-curve” measurements to a high of 3.60 for examiner A’s and examiner B’s tape “not-over-the-cunre”mearurements. The larwt maximal difference was 11.5 cm for examiner A’s and examinor C’s tape “over-the-curve” rneas”reme”ts.
Comparison of pairs of examiners demonstrated that examiner A and examiner D tended to have the smallest mean absolute differences. Comparison of the three measurement techniques demonstrated that tzye “over-the-curve” and the callper techniques had the smallest differences.
DISCUSSION These findings indicate that fundal height measurements are more reliable when they are obtained by the sane clinician than when they are obtained by different clinicians. Previous investigator have also reported that lntraexaminer differences are smaller than interexamIner differences (10-121. Thus, these studies
supporttherecommendation that the same cllnlcian should obtain fundal height measurements on the same u.ornanthroughoutpreg”a”cy (3.15). These Andings also suggest that caliper measurements may be more reliable than measurements obtained with a tape measure. Of the two previous studies that compared the reliability of calipers to tape rneawres. one study (6) found that the differences in caliper measurements were smaller than the differences between tape measurements. However, the other study (5) found that the two methods were not remarkablv different. Thus, the merits of using a caliper rather than a tape rneanxe need to be evaluated further. Although some textbooks imply that caliper mea s”rerrle”ts are superior to tape measurements 13). there are no published studies that have demonstrated that caliper measurements are more accur&e than tape measures in assessirw fetal size or in identttins other pr&nancy complications. theuse of calipers clinically would ako present problems such as the cost of the instrument and issues related to how the instrument is cleaned between patients. Studies comparing the predictive accuracy of calipers and tape measures must be conducted before the use of calipers is recommended in clinical praactice. Regardlw of which technique is used to measure fundal height. the magnitude of differences within and between examiners observed i- this and In other stud&s (6, 7. 101 1sof concern. Because of the amount of measurement error, clinicians should do everything possible to improve the reliability of their measurements. Specific suggestionsfor improving the reliability of fundal height measurements k&de the following: 1. Clinicians should have wrttten protocok that explicitly describe how fundal height should be measured, and all clinicians in that setting must agree upon and use the recommended technique.
TABLE 2
Meescremenr
ond Examiner Pair
n*
MALI
Tape “over-the-curve” Exaai~ A and ExaminerB 22 2 19 1.44 1.73 Set 2 20 1.82 ExaminerA and Examinerc Set 1 20 256 3.40 2.64 Set2 20 2.51 ExammerA and ExammerD 1.14 Set 1 18 1.40 set2 18 1.86 201 *wrage+
1.79 1.69
4.5
57
27.3 35.0
59.1 65.0
2.58 2.27
L1.5 9.1
300 20.0
60.0 55.0
1.20 1.58
z.:
33.9 27.8
72.2 50.0
2.79 2.47
6.2 7.2
9.1 15.0
13.6 35.0
2.62 2.36
7.3 8.8
lC.0 400
30.0 55.0
1.26 128
4.3 3.3
55.6 33.9
72.2 66.7
2.69 2.59
2.37 2.40
7.5 6.9
18.2 15.0
45.5 25.0
3 11 176
2.26 I.45
7.0 4.8
15.0 55.0
55.0 70.0
1.74 1.66
1.23 1.35
4.6 4.0
44.4 47.1
77.0 76.5
206
Tape “not-the-overxurw” Ex∋er A and ExaminerB 22 3.60 1.65 1.95 Set 2 20 2.93 ExaminerA and ExaminerC 2.97 Set 1 20 3.22 337 set2 20 2.40 ExaminerA and ExaminerD 1.58 set 1 18 136 1.64 Set 2 18 1.61 AVemge
2.50
Caliper Examiner A and ExaminerB
set 1 22 2.77 Set 2 20 3.05 Exx,$er A and20 Examiner 258 C set2
20
1.52
Exaai;“’ A and18 Examiner 1.37 D set2 17 152 Average
2.14
2. Clinicians need to identify the landmarksusedinthemeasuringpmcess carefully to make sure that they have accurate!y identified the landmarks. This means that the woman’s abdomen and pubic area must be sutftciently exposed to allow the dnician to identify the lzdmark and place the tape measure without hav-
ing to stntggle with pulling back or holding up the wman’s cbthing. 3. The notion that fundal height should be measured mare than once on the smne woman at each prenatal visit merits consideration. G&I the am-auntof error in fundal hetght meawrem&sobsetwdtntandinoUwzr studies, accuracy of measurements
may be Increased if the measurements are obtained more than once. The findings from this study indicate that some clinicians and pairs of clinicians have smaller differences. AddMonaUy, other investigators (f&9, 121 have reDotied smaller differencxa within and between clinicians’ measurements. Thus, thse findings sugg&that the in&r- and interexaminer reliabiity of fundal height measurements can be improved. It 1sImperative that clinicians and researchen investigate methods of improving the reliability of fundal height measurement&
merits. Future studies must evaluate the reliablllty and validity of the various fundal height meawrement techniques, particularly the caliper technique because preliminary studies indicate that measurements obtained with calipers may be more reliable than those obtained with tape measures. Such studies will allow clinicians to choose the most reliable and valid method of measuring fundal height.
22
8. Beliian JM. Villar J. Nardin JC, M&mud J, Salnr de Vkuna L. Dk.gm,ds of lntmuteline growth retardation by a simple clinical method: nleasurelne”tof uterine height. Am J Obstet Gynecol 1978;131:64&5. 9. RogersMS, Needham PG. Evaluation of fundal height measurementin antenatal care. Aust N Z J Obstet Gynaecol 1985;25:87-90. 10. Baw W, EriksenPS. SecherNJ, ThistedJ. WestergaardL. The precision and accuracyof symphysis-fundusdistance mearurementsduring pregnancy. ActaObstetGunecolScand1985:64:3714.
SUMMARY Because the notdity of foodal height measurementsis determined by evaluating the indiidual woman’s pattern of fundal growth and by comparing fundal height measurements to established limits of nom-ml, reliibiitv within and between clinicians is essential for safe clinical practice. In the absence of intm and interexaminer r&ability. pregnancy complications may be overlooked and uncomplicated pregnancies may be subjected to unnecessay diagnostic procedures. The results of this and other studies indicate that the dlfferences within and behveen clinicians’ measurements are greater than what would be considered acceptable for safe clinical practice. Thus. clinicians must do everything possible to improve the rellabilliy of their measure-
7. B&au SM. SamwndalP. GrantJM. A cornpa& oi three methbds of assessing inter-obsewer variation applkd to measurementof the symphyris-fun&l heiqht. Br J Obstet Gvnaecol 1989: 96126&71.
REFERENCES 1. EngstromJL. Assessmentof the reliabilityof $-~ysicalmeasures.F&sNurs Health 1988;11:3B%9. 2. Potit DF. Hun&r BP. Nursingresearch:pdndpies a4 methods.Brded. Philadelphia:Liwincott. 1987. 3. &mey H. Nurse-midwtfey. 2nd ed. Boston.Bk&well ScientificF’ublkrlion& 1937. 4. PendletonGF. A studyof the contour abdominal of pregnancy. Am J Obetet Gwecol 1926: 12:3’%-414.
measuremnt
5. Be-&y JM, Underhill R4. Fallacy of the fundal height. BMJ 1970;4:40& 6. 6. Crosby ME, En&mm JL Interexaminerreliabilityin fundal heightmeasurement. Mldwtver Chron Nws Note 1989;102%?-6.
Joumat of Nurse-Midwifery .
11. Calvert JP, Crean EE, Newcombe RG, PearsonJF. Antenatalsmeeningby measurement of qmphykhmdw tresht BMJ 1982;285:B4&9. 12. Pxhem H. Sod&erg G. Es& mationof fetalweightby al&minal measurements. Acta ObstetGynecol Sand 1984;63:175-9.
external
13. EngstromJL. Fundal height and abdominal @th measurementsdting weg”ancy [d&oral dksetitationl. Chic?@: univ. of tuirmisat Chit, 1985. 14. Bland JM, Alhnan DG. Sta!kkal methods fw assessingagreement between two methodsof dintcal measurement Lancet 1986;1:307-10. 1.5. Adams CJ. Prognany. In: Adams CJ, editor. Nurse-midwifery:health care for women and newborns. New York: Grune & Skatton, 1983.
Vol. 38. No. 1. JanuarylFebruw 1593