ABSTRACT PURPOSE METHODS RESULTS CONCLUSION INTRODUCTION CORRESPONDING AUTHOR 550

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1 Percetage Chage i Ateatal Body Mass Idex as a Predictor of Neoatal Macrosomia Chad A. Asplud, MD 1 Dea A. Seehuse, MD, MPH 1 Terra L. Callaha, MD 1 Cara Olse, MS, MPH 2 1 Eisehower Army Medical Ceter, Fort Gordo, Georgia 2 Uiformed Services Uiversity of the Health Scieces, Bethesda, Marylad ABSTRACT PURPOSE We wated to evaluate the predictive value of percetage chage i ateatal materal body mass idex (BMI) as it relates to macrosomia, as well as to compare chage i pregacy BMI with existig weight gai guidelies. METHODS We aalyzed data from 6 moths of cosecutive deliveries, focusig o first visit (first trimester) BMI, last visit (37 weeks or later) BMI, ad fetal birth weight. Usig regressio ad χ 2 aalyses, we evaluated the relatioship betwee chage i BMI ad macrosomia. RESULTS Of the 238 cosecutive deliveries, we were able to aalyze data from 186, of which 15.6% ( = 29) of the ifats were macrosomic. Amog macrosomic ifats, 86.2% (25/29) of their mothers had a 25% or greater icrease i BMI compared with 6.6% (10/157) of mothers of ormal-weight ifats (P <.001), for a relative risk 13.5% (95% cofidece iterval [CI], 7.3%-25.1%). Percetage chage i BMI of 25% or greater had a sesitivity of 86.2% (95% CI, 68.3%-96.1%), a specificity of 93.6% (95% CI, 88.6%-96.9%), a positive predictive value of 71.4% (95% CI, 53.7%-85.4%), ad a egative predictive value 97.4% (95% CI, 93.4%-99.3%) for macrosomia. Logistic regressio adjusted for materal age, race, parity, ad gravidity showed that those wome whose BMI icreased 25% or greater were more tha 200 times more likely (odds ratio [OR] = 219.3; 95% CI, ,238.6; P <.001) to give birth to a macrosomic ifat. Further adjustig for iitial BMI stregtheed the associatio (OR = 1,062.4; 95% CI, ,572.2; P < 001). Regardless of weight gai, whe compared with Istitute of Medicie weight gai recommedatios, chage i BMI or 25% or greater was associated with macrosomia (P <.001). CONCLUSION Idepedet of iitial pregacy BMI or absolute weight gai, a icrease i materal BMI of 25% or greater durig pregacy is highly predictive of macrosomia. A Fam Med 2008:6; DOI: /afm.903. Cofl icts of iterest: oe reported CORRESPONDING AUTHOR Chad Asplud, MD Departmet of Family Medicie Eisehower Army Medical Ceter Fort Gordo, GA chad.asplud@osumc.edu INTRODUCTION Neoatal macrosomia affects betwee 3% ad 15% of all pregacies ad is associated with shoulder dystocia, brachial plexus ijury, skeletal ijuries, mecoium aspiratio, periatal asphyxia, hypoglycemia, ad fetal death. 1,2 Materal complicatios of macrosomia iclude prologed labor, labor augmetatio with oxytoci, cesarea delivery, postpartum hemorrhage, ifectio, 3rd- ad 4th-degree laceratios, thromboembolic evets, ad aesthetic accidets. 2 Materal obesity, multiparity, previous macrosomic ifat, male fetus, materal birth weight, materal diabetes, prepregacy body mass idex (BMI), ad excessive materal weight gai are all risk factors for fetal macrosomia. 1,3 Although materal weight gai is frequetly cited as a risk factor for macrosomia, 3 curret weight gai recommedatios 4 ad cosesus guidelies ad are ot evidece based. Additioally, there exist substatial variatio i the literature ad limited evidece supportig the stregth of associatio betwee these risk factors ad macrosomia

2 The purpose of this study was to evaluate the predictive value of percetage chage i atepartum materal BMI i predictig eoatal macrosomia, as well as to compare chage i atepartum materal BMI with existig weight gai guidelies. METHODS Based o persoal experiece ad a small pilot study, we hypothesized that a icrease i ateatal BMI by greater tha 25% may be a predictor of macrosomia. The protocol was approved by the Eisehower Army Medical Ceter (EAMC) istitutioal review board. We studied military beefi ciaries whose babies were delivered by EAMC physicias from Jue 2006 to December The mai eligibility criterio was the delivery of a live-bor fetus at 37 to 42 weeks gestatio. Exclusio criteria icluded gestatioal diabetes, multiple gestatio, etry to care after the fi rst trimester, delivery before 37 weeks, or charts missig ay of the data poits. Sample size for a power of 0.80 ad a α of.05 was determied by usig the lower ed of the America College of Obstetrics ad Gyecology (ACOG) supported prevalece of fetal macrosomia of 10% plus a coservative value of relative risk supported i the literature of 2.5 (rage, ), 1,2,6 which yielded a desired sample size of 151 deliveries (calculatio was performed o statistical calculator at stat.ubc.ca/~rolli/stats/ssize/caco.html.) Demographic ad pregacy data were gathered from the electroic medical record. Ifats were weighed o a Scale-Troix scale (Scale-Troix, Ic, White Plais, New York) withi 1 hour of birth. BMI was calculated by the electroic medical record usig the stadard formula (weight [kg] / height [m 2 ]) ad recorded. Data were etered ito a Excel spreadsheet (Microsoft Corp, Redmod, Washigto) ad reviewed by a coauthor for accuracy. Cotigecy table aalyses icluded χ 2 aalysis ad Fisher s exact test to assess for sigifi cat associatio betwee percetage chage i BMI ad macrosomia. We used logistic regressio aalysis to compute the associatio betwee percetage chage i BMI ad fetal weight ad compared percetage chage i BMI with curret weight gai guidelies. We used receiver operator character (ROC) curve aalysis to assess the accuracy of this BMI AND NEONATAL MACROSOMIA techique for predictig a fetal of weight greater tha 4,000 g. SPSS 12.0 (SPSS Ic, Chicago, Illiois) was used for all data aalyses. RESULTS A total of 238 EAMC deliveries occurred from Jue 2006 to December Fifty-two were excluded (30 were late etries to care, 13 mothers had gestatioal diabetes, 6 fi les had missig data, ad 3 were multiple gestatios). Amog the 186 icluded i the fi al aalysis, 56.5% of mothers were white ad 25.8% were black. Average materal age was 26.5 years; 32.8% were primigravidas. (Table 1) Of the 186 ifats, 15.6% were macrosomic ( = 29). Of those macrosomic ifats, 86.2% (25/29) of their mothers had a percetage chage i ateatal BMI of 25% or greater compared with 6.6% (10/157) of the mothers of ormal-weight ifats (P <.001), which yielded a relative risk 13.5 (95% cofi dece iterval [CI], 7.3%-25.1%). Percetage chage i ateatal materal BMI of 25% or greater had a sesitivity of 86.2% (95% CI, 68.3%-96.1%), specifi city of 93.6% (95% CI, 88.6%-96.9%), a positive predictive value of 71.4% (95% CI, 53.7%-85.4%), ad a egative predic- Table 1. Compariso of Ateatal Patiets With ad Without Macrosomic Ifats Characteristic Normal Weight ( = 157) Macrosomic ( = 29) P Value Age, mea y (SD) 26.6 (5.1) 25.9 (4.6).527 Age, (%).378 <25 y 64 (40.8) 12 (41.4) y 55 (35.0) 11 (37.9) y 24 (15.3) 6 (20.7) 35 y 14 (8.9) 0 (0) Race, (%).274 White 86 (54.8) 19 (65.5) Black 44 (28.0) 4 (13.8) Other 27 (17.2) 6 (20.7) Parity, (%) (43.3) 11 (37.9) 1 51 (32.5) 13 (44.8) (24.2) 5 (17.2) Gravidity, (%) (33.1) 9 (31.0) 2 46 (29.3) 8 (27.6) (37.6) 12 (41.4) BMI Iitial (SD) 25.8 (5.09) 25.3 (5.43).625 Fial (SD) 30.6 (4.98) 33.9 (5.13).001 % chage 15.6 (6.44) 25.5 (6.59) <.001 Birth weight, g (SD) 3,332 (345) 4,244 (243) <.001 P values based o t test (for meas) or χ 2 test (for proportios). 551

3 tive value of 97.4% (95% CI, 93.4%-99.3%) for the predictio of eoatal macrosomia. Receiver operator characteristic (ROC) curve aalysis showed a area uder the curve of 0.89 (Figure 1). Mother s age, race, parity, ad gravidity were etered ito a multivariate logistic regressio model, alog with a idicator for materal BMI chage of 25% or greater. After adjustig for other materal characteristics, the odds of givig birth to a macrosomic ifat were more tha 200 times higher amog mothers whose BMI icreased at least 25%, (odds ratio [OR] = 219.3; 95% CI, ,238.6; P <.001). Noe of the other variables reached statistical sigifi cace at the 5% level. Fially, after adjustig for iitial BMI, the associatio was eve stroger (adjusted OR = 1,062.4; 95% CI, ,572.2; P <.001). Iteractios betwee BMI chage ad other materal characteristics were ot statistically sigifi cat. The data were further stratifi ed by etry BMI ad evaluated agaist the existig Istitute of Medicie (IOM) weight gai guidelies. 4 (Table 2) Gaiig weight i excess of the IOM recommedatios was a weaker predictor of macrosomia tha percetage chage i materal BMI of 25% or greater. Furthermore, 11% of wome whose weight gai was withi or below the IOM guidelies also gave birth to macrosomic ifats. Of these, 71% would have bee predicted by a 25% or greater ateatal icrease i BMI. DISCUSSION Although there is cosiderable variatio i the defi itio of macrosomia i the literature, 6 4,000 g is the most widely used value ad is the value at which materal ad eoatal complicatios icrease. 7 It is also the most commo weight used whe evaluatig the predictive value of various methods to determie macrosomia ateatally. 7 Because oe goal was to compare our method BMI AND NEONATAL MACROSOMIA with those already published, we also chose 4,000 g as our defi itio of macrosomia. Several studies have foud materal estimate of birth weight offers a sesitivity of approximately Figure 1. Receiver operator characteristic (ROC) curve of sesitivity of percetage chage i body mass idex (BMI) of 25% vs specificity. Sesitivity Table 2. Aggregate Data Comparig Macrosomia Withi IOM Guidelies IOM Guidelies Macrosomic Normal Weight Total Weight gai less tha IOM recommedatios a Chage i BMI 25% Chage i BMI <25% Total Weight gai withi IOM recommedatios b Chage i BMI 25% Chage i BMI <25% Total Weight gai greater tha IOM recommedatios c Chage i BMI 25% Chage i BMI <25% Total BMI = body mass idex; IOM = Istitute of Medicie. P < Specificity Source of the Curve 1st BMI Last BMI Percet chage Referece lie a Sesitivity = 75%, specificity = 100%, positive predictive value = 100%, egative predictive value = 98%. b Sesitivity = 70%, specificity = 97%, positive predictive value = 78%, egative predictive value = 96%. c Sesitivity = 100%, specificity = 84%, positive predictive value = 68%, egative predictive value = 100%. 552

4 BMI AND NEONATAL MACROSOMIA 56%. 8,9 Cliical palpatio is the traditioal method used, but this method has a sesitivity similar to that of materal estimate ad is kow to have a large predictive error, especially with large ifats. 10 Risk factor assessmet has also bee studied, but it has poor sesitivity ad specifi city. 1 There have also bee may studies of the use of soography, with may differet fetal measuremet algorithms used, 4 of which specifically looked at predictio of eoatal macrosomia These studies showed a sesitivity of 59%, with area uder the ROC curves from Fially, several birthweight predictio algorithms have bee used, with a sesitivity of 54% to 58% ad a specifi city of 84% to 92%. 11,16 Previous studies have suggested that obesity before pregacy cotributes to macrosomia, ad whe prepregacy BMI icreases, there is a icrease i eoatal macrosomia ad poor delivery outcomes Although prepregacy BMI ad materal weight gai correlate with fetal birth weight, our fi digs suggest that percetage chage i materal BMI may offer a better estimatio of overall chage i materal body compositio ad fetal weight. Our report appears to be the fi rst published study showig that ateatal icrease i BMI of 25% or greater is a sesitive predictor of fetal macrosomia, regardless of iitial BMI. Also, BMI is calculated by most electroic medical chartig systems ad is readily available to cliicias at poit of care. Although the previous methods are accurate ad have cliical utility, may of them require special equipmet or formulas, ad oe is sigularly predictive. Our lowtech method may be used as a sole predictor of eoatal macrosomia or to augmet other methods, such as palpatio, soography, or predictio equatios. Guidelies for materal weight gai have existed sice the 1990 IOM report recommedig weight gai for a specifi c prepregacy BMI category (Table 3), which the ACOG adopted i ,20 Materal weight gai recommedatios, however, were based o observatioal studies i a attempt to balace the beefi ts of icreased fetal growth with the risks of complicated labor ad delivery, ad the recommedatios were ot evidece-based. 4 Usig our method, the upper limit of weight gai may be idividualized for obstetric patiets. For example, for a 5 foot 1 ich tall woma who started pregacy at a weight of 110 pouds (BMI = 20.8), a icrease i BMI of 25% (BMI = 26.0) would be caused by a weight gai of 27 pouds; therefore, 27 pouds could be used as the upper limit of weight gai, compared with the 35 to 40 pouds recommeded by the IOM guidelies. The limitatios of our study iclude our uique patiet populatio ad their access to medical care. Our military populatio has good access to care at Table 3. Istitute of Medicie (IOM) Guidelies for Weight Gai i Pregacy Iitial Body Mass Idex IOM Recommeded Weight Gai, lb <19.8 (uderweight) (ormal) (overweight) >29.0 (obese) At least 15 From the Istitute of Medicie. 4 o cost, may be more physically fi t tha the civilia sector, ad may possess lower prepregacy weight ad weight gai durig pregacy. Also, i a effort to miimize cofouders, we excluded wome with gestatioal diabetes. This exclusio may be viewed as a limitatio, because detectig macrosomia i diabetic patiets may actually help to direct maagemet decisios. I coclusio, fetal macrosomia has bee cosistetly associated with eoatal ad materal complicatios. Ay idicator that helps diagose macrosomia may allow cliicias to make better choices regardig timig ad mode of delivery, as well as prepare for emergecies. Our fi digs support that regardless of iitial pregacy BMI or total amout of materal weight gai, a atepartum materal BMI icrease of 25% or greater is predictive of eoatal weight greater tha 4,000 g. This method is easy to use without ay special equipmet or expert cliical skills, ad it has show a better sesitivity ad specifi city tha previously described methods. Fially, our method may allow cliicias to idividualize materal weight gai recommedatios, replacig previous IOM guidelies. Ateatal percetage chage i BMI was highly predictive of macrosomia i our uique patiet populatio. Future studies i a larger, more heterogeeous populatio are eeded. Prospective studies will be desirable to test ateatal chage i BMI as a meas for ifl uecig materal weight gai ad detectig ad maagig delivery of macrosomic fetuses. To read or post commetaries i respose to this article, see it olie at Key words: Fetal macrosomia; body mass idex; pregacy Submitted November 5, 2007; submitted, revised, Jue 5, 2008; accepted Jue 10, Phase 1 of this study was preseted at the North America Primary Care Research Group (NAPCRG) Aual Meetig, Vacouver, British Columbia, October 22, The complete study was preseted at the Uiformed Services Academy of Family Physicias Aual Meetig, Portlad, Orego, March

5 BMI AND NEONATAL MACROSOMIA Refereces 1. Golditch IM, Kirkma K. The large fetus. Maagemet ad outcome. Obstet Gyecol. 1978;52(1): Boulet SL, Alexader GR, Salihu HM, et al. Macrosomic births i the Uited States: determiats, outcomes, ad proposed grades of risk. Am J Obstet Gyecol. 2003;188(5): Spellacy WN, Miller S, Wiegar A, et al. Macrosomia-materal characteristics ad ifat complicatios. Obstet Gyecol. 1985;66(2): Istitute of Medicie (Uited States) Subcommittee o Nutritioal Status ad Weight Gai Durig Pregacy. Nutritio Durig Pregacy. Washigto, DC: Natioal Academy Press; Sacks DA, Che W. Estimatig fetal weight i the maagemet of macrosomia. Obstet Gyecol Surv. 2000;55(4): Nahum GG. Detectig ad maagig fetal macrosomia. Cotemp Ob Gy. 2000;6: America College of Obstetricias ad Gyecologists (ACOG). Fetal macrosomia. Washigto, DC: America College of Obstetricias ad Gyecologists (ACOG); ACOG practice bulleti; o Herrero RL, Fitzsimmos J. Estimated fetal weight. Materal vs. physicia estimate. J Reprod Med. 1999;44(8): Chauha SP, Cowa BD, Maga EF, et al. Itrapartum detectio of a macrosomic fetus: cliical versus 8 soographic models. Aust N Z J Obstet Gyaecol. 1995;35(3): Og HC, Se DK. Cliical estimatio of fetal weight. Am J Obstet Gyecol. 1972;112(7): Wikstrom I, Bergstrom R, Bakketeig L, et al. Predictio of high birthweight from materal characteristics, symphysis fudal height ad ultrasoud biometry. Gyecol Obstet Ivest. 1993;35(1): Chauha SP, West DJ, Scardo JA, et al. Atepartum detectio of macrosomic fetus: cliical versus soographic, icludig soft-tissue measuremets. Obstet Gyecol. 2000;95(5): Pollack RN, Hauer-Pollack G, Divo MY. Macrosomia i postdates pregacies: the accuracy of routie ultrasoographic screeig. Am J Obstet Gyecol. 1992;167(1): O Reilly-Gree CP, Divo MY. Receiver operator characteristic curves of soographic estimated fetal weight for predictio of macrosomia i prologed pregacies. Ultrasoud Obstet Gyecol. 1997;9(6): Chauha SP, Grobma WA, Gherma RA, et al. Suspicio ad treatmet of macrosomic fetus: a review. Am J Obstet Gyecol. 2005;193(2): Nahum GG, Staislaw H, Huffaker BJ. Accurate predictio of term birth weight from prospectively measurable materal characteristics. J Reprod Med. 1999;44(8): Cattigius S, Bergstrom R, Lipworth L, et al. Prepregacy weight ad the risk of adverse pregacy outcomes. N Egl J Med. 1998;338(3): Wolfe H. High prepregacy body-mass idex a materal-fetal risk factor. N Egl J Med. 1998;338(3): Jese DM, Damm P, Sorese B, et al. Pregacy outcome ad prepregacy body mass idex i 2549 glucose-tolerat Daish wome. Am J Obstet Gyecol. 2003;189(1): America College of Obstetricias ad Gyecologists. Nutritio Durig Pregacy. Washigto, DC: America College of Obstetricias ad Gyecologists, 1993; Techical Bulleti o