Poster session II Diabetes, labor, medical-surgical-disease, obstetric quality & safety, prematurity, ultrasound-imaging: Abstracts 237 – 386| Volume 206, ISSUE 1, SUPPLEMENT , S158, January 01, 2012

336: Ultrasound derived estimated fetal weight using customized standards: does it improve prediction of adverse pregnancy outcomes?


      Customized birth weight standards have been shown to be better associated with adverse pregnancy outcomes compared to population-based standards. Our purpose was to estimate the rate of suboptimal fetal growth identified by prenatal ultrasound estimated fetal weight (EFW) utilizing customized standards compared to population-based standards and determine whether there is improved prediction of adverse pregnancy outcomes utilizing these methods.

      Study Design

      We performed a retrospective cohort study of all women who underwent prenatal ultrasound examination at ≥ 24 weeks 0 days with a live fetus and delivered at a tertiary care hospital from July 1, 2010 to June 31, 2011. Cases with major structural fetal anomalies were excluded. Ultrasound-derived EFW and growth percentiles (popEFW) were reported utilizing the Hadlock formula and the percentile table devised by Williams et al. (Obstet Gynecol 1982. 59:624-32). A customized EFW (custEFW) was calculated adjusting for maternal height, weight, ethnicity, parity, and fetal sex ( The frequency of small for gestational age (SGA) defined as EFW <10th%ile, was compared between methods. Secondary outcomes studied were SGA by customized newborn weight, preterm birth (PTB) <37 weeks, PTB <34 weeks, cesarean delivery (CD), and neonatal intensive care (NICU) admission.


      A total of 782 women met inclusion criteria. On prenatal ultrasound, more fetuses were identified as SGA using custEFW compared to popEFW (15.1% vs. 3.8%; p= <0.0001). Of those with prenatal SGA, 48.4% of custEFW and 14.8% of popEFW were diagnosed as SGA by customized newborn weight. All secondary outcome measures were more frequent among those diagnosed as SGA by custEFW (Table).
      Tabled 1
      Table thumbnail grt46


      This is the first study to date using custEFW centiles for prenatal ultrasound diagnosis of abnormal fetal growth. When comparing the popEFW centile to the custEFW centiles, custEFW demonstrated markedly higher rates of adverse pregnancy outcomes compared to the population standard.