OBSTETRICS Combined analysis with amniotic fluid index and estimated fetal weight for prediction of severe macrosomia at birth Rinat Hackmon, MD; Eran Bornstein, MD; Asaf Ferber, MD; Javine Horani, MD; Christopher P. O’Reilly Green, MD; Michael Y. Divon, MD OBJECTIVE: To evaluate combined analysis with amniotic fluid index (AFI) and estimated fetal weight (EFW) for prediction of severe macro- somia at birth. STUDY DESIGN: In this retrospective case-control study, 50 term se- vere macrosomic newborns (birthweight [BW]  97th percentile) were included in the study group and 100 appropriate for gestational age newborns served as controls. All pregnancies underwent a third-tri- mester sonographic evaluation in which AFI and EFW were measured. The association between BW and AFI and EFW percentiles was exam- ined. The statistical analysis included Student t test, simple regression and receiver-operating curve analyses, and 22 tables. RESULTS: The mean mid-third-trimester AFI percentile and EFW per- centile in severe macrosomic infants were 72.4  22.5 and 83  12, respectively, which was significantly higher than in controls (P  .0001). Significant correlations were detected between BW and AFI and EFW percentiles (r = 0.44 and r = 0.72, respectively; P  .0001). Receiver-operating characteristic analysis identified AFI  60th percentile and EFW  71st percentile as best predictors of severe macrosomia. The combined analysis with AFI  60th percentile and EFW  71st percentile resulted in a positive predictive value of 85%. CONCLUSION: There is a significant correlation between mid-third-tri- mester AFI and BW. AFI  60th percentile and EFW  71st percentile during the mid third trimester are useful predictors of severe macroso- mia at birth. Key words: amniotic fluid index (AFI), combined third-trimester AFI and EFW analysis, estimated fetal weight (EFW), severe fetal macrosomia Cite this article as: Hackmon R, Bornstein E, Ferber A, Horani J, O’Reilly Green CP, Divon MY. Combined analysis with amniotic fluid index and estimated fetal weight for prediction of severe macrosomia at birth. Am J Obstet Gynecol 2007;196:333.e1-333.e4. F etal macrosomia, traditionally de- fined as birthweight (BW)  4000 is associated with a moderate increase in perinatal complications, including perinatal mortality, asphyxial injuries, meconium aspiration, prolonged la- bor, shoulder dystocia, soft tissue trauma, humeral and clavicular frac- tures, brachial plexus and facial pal- sies. 1,2 These risks increase dra- matically with BW  4500 g. 3-5 Unfortunately, the accuracy of sono- graphic estimated fetal weight (EFW) in the diagnosis of macrosomia is sub- optimal, with a positive predictive value (PPV) of 38-67%. 6-8 The sonographic assessment of amni- otic fluid in the third trimester is an in- tegral component of the fetal biophysical profile and as such is essential in estab- lishing fetal well-being. Fetal urination plays an important role in the produc- tion of amniotic fluid during the second and third trimesters. 9,10 The association between body weight and urinary output is a well known physiological phenom- ena and has been described in human ne- onates. 11 Indeed, several studies report an association between the amniotic fluid index (AFI) near delivery and fetal weight. Sylvestre and Divon 12 reported that AFI in nondiabetic, postterm patients is strongly dependent on BW. Further- more, Myles and Nguyen 13 reported that an increasing AFI in term pregnancies correlates linearly with increasing BW. They found that AFI  15 and  18 cm was associated with a 2- and 6-fold in- crease, respectively, in the risk of macro- somia at birth. In a study of 35 large for gestational age (LGA) and 377 control pregnancies with sonography performed within 1 week of delivery, Benson et al 14 con- cluded that polyhydramnios occurred more frequently in LGA pregnancies (17% vs 8%, respectively), but had lit- tle effect on the PPV of an EFW  90th percentile. They suggested that, to en- hance the predictive value of EFW in macrosomia, amniotic fluid volume can be used in a complementary fash- ion; that is, when the EFW  90th per- centile, LGA can be diagnosed with greater confidence in the presence of polyhydramnios. 2,14 Our objective was to define third-tri- mester percentiles of AFI and EFW that, when combined, improve the prediction of severe macrosomia. MATERIALS AND METHODS Data for this retrospective case-control study were obtained from a computer- From the Department of Obstetrics and Gynecology, Lenox Hill Hospital, New York, NY. Received June 21, 2006; received in revised form Oct. 2, 2006; accepted Nov. 18, 2006. Reprints: Rinat Hackmon, MD, Department of Obstetrics and Gynecology, Lenox Hill Hospital, 130 E. 77 St, New York, NY 10025; rinatia@netvision.net.il 0002-9378/$32.00 © 2007 Mosby, Inc. All rights reserved. doi: 10.1016/j.ajog.2006.11.019 Research www. AJOG.org APRIL 2007 American Journal of Obstetrics & Gynecology 333.e1