Abstract： Objective To study the risk factors of obstetrical brachial plexus palsy (OBPP).Methods Forty-six newborn infants with OBPP were recruited between January 1997 and December 2009 from Technical Appraisement Center for Medical Malpractice of Shandong province as OBPP group.In the control group,138 newborn infants delivered in the same time,same hospital and same gender were collected,with a ratio of 1:3.All the cases were analyzed retrospectively.The newborn,maternal,childbirth data and working experience of midwives were analyzed by univariate and multivariate logistic regression analysis.Results ( 1 ) External pelvimetries of the two groups were normal.All were singleton newborns by vaginal deliveries with cephalic presentation.Twenty-two newborns had left unilateral palsies,and the other 24 had right unilateral palsies.The numbers of the whole,upper and fore arm type were 17,26 and 3,respectively.The maternal age,gravidity,parity and gestational weeks were higher in OBPP group than in the control group ( P ＜ 0.05 ).( 2 ) The maternal antepartum body mass index ( BMI ) [ ( 29.5 ± 2.4 ) kg/m2 ],height of the uterus [ (34.9 ± 2.4) cm ] and abdominal circumference [ ( 105 ± 6) cm ] in OBPP group were higher than those in the control group [ ( 26.1 ± 2.5 ) kg/m2,( 33.7 ± 2.2 ) cm and ( 99 ± 5 ) cm,respectively ] ( P ＜ 0.05 ).The newborn birth weight in OBPP group [ ( 4390 ± 489 ) g ] was significantly higher than the control group [ ( 3404 ± 360 ) g] ( P ＜ 0.01 ).The working experience of midwives in OBPP group [ ( 5.2 ± 2.3 ) years ] was less than the control group [ ( 8.9 ± 5.4) years ] ( P ＜ 0.01 ).(3) There was a higher proportion of instrumental delivery ( 28.3％ vs.3.6％ ),uterine atony (28.3％ vs.6.5％ ),prolonged second stage(8.7％ vs.0.7％ ) and fetal malposition( 10.9％ vs.2.9％ ) in the OBPP group than in the control group ( P ＜ 0.05 ).(4) Univariate logistic analysis showed that the P values of maternal age,antepartum BMI,height of uterus,abdominal circumference,newborn birth weight,gravidity,second stage duration,instrumental delivery,fetal malposition,uterine atony and working experience of midwives were all less than 0.10.And the working experience of midwives was a protective factor.(5)The factors listed above were taken as variables,selected stepwise regression for multivariate logistic regression analysis.Boundary value was 0.10.It showed that the antepartum BMI ( OR =1.733 ) and newborn birth weight ( OR =1.004 ) were related to OBPP ( P ＜ 0.10 ).The significance of maternal antepartum BMI was higher than birth weight.Conclusions The maternal antepartum BMI is the most important risk factor for OBPP,and the newborn birth weight is the other risk factor.The working experience of midwives is a protective factor.