Objective To explore the significance of fetal ultrasonic biological Z-scores for assessing fetal growth in the mid and late pregnancy. Methods This was a retrospective study.Women who delivered in Shenzhen Hospital affiliated to Southern medical university between January 2016 and April 2017 were enrolled.Several groups were screened out and selected as observation groups among them there were 103 mothers of macrosomic fetuses (macrosomia group,including 25 mothers with GDM and 78 mothers with normal pregnancy),48 mothers of fetal growth retardation(FGR group),and 169 mothers of normal birth weight infants(these mothers with GDM controled their blood sugar well,and were selected for GDM-normal weight group).Other 196 mothers of normal birth weight infants had normal pregnany,and were selected as control group.The fetal abdominal circumference(AC),head circumference(HC),biparietal diameter(BPD) and femoral length (FL) were measured at 20+1-24, 28+1-33 weeks and 34+1weeks to delivery under prenatal ultrasound.The ratio of HC to AC (HC/AC) and AC Z-score were calculated.The BPD,HC,AC,FL,HC/AC ratio and AC Z-scores between observation groups and control group were compared.The HC/AC ratio Z-scores between macrosomic fetuses of mothers with GDM(GDM- macrosomia group) and macrosomic fetuses of mothers with normal pregnancy(normal- macrosomia group) were compared.T test was used for statistical analysis between groups. Results At 20+1-24, 28+1-33 weeks and 34+1weeks to delivery,the AC Z-scores of macrosomia group were higher than that of the control group,and the AC Z-scores of FGR group were lower than that of the control group (both P<0.05).The AC Z-scores of macrosomia group showed a progressive increase,and the AC Z-scores of FGR group declined progressively. The AC Z-scores had no obvious difference in the GDM-normal weight group and the control group at 20+1-24 and 28+1-33 weeks.The difference between this two groups was statistically significant at 34+1weeks to delivery, AC Z-scores of GDM-normal weight group were slightly higher than that of the control group(P=0.045).At 34+1weeks to delivery,the HC/AC ratio Z-scores of GDM- macrosomia group were higher than that of normal- macrosomia group(P<0.05). As to traditional ultrasonic biological parameters,only the AC of macrosomia group was different from that of the con- Troll group at 20+1-24 weeks(P<0.05),and the AC of FGR group was not. At 28+1-33 weeks and 34+1weeks to delivery,the BPD, HC,AC,FL,HC/AC of macrosomia group and FGR group were different from those of the control group(P<0.05).But the degree of data values deviating from the means can not be shown visually with traditional ultrasonic biological parameters. Conclusions The fetal ultrasonic biological Z-scores can provide quantitative evidence in fetal growth,and evaluate fetal developmental outcomes more accurately and effectively.