title: An adjustable fetal weight standard for twins: a statistical modeling study.
abstract: BACKGROUND
  It is a common practice to use a singleton fetal growth standard to assess twin growth. We aim to create a twin fetal weight standard which is also adjustable for race/ethnicity and other factors.
  
  
  METHODS
  Over half a million twin births of low risk pregnancies in the US, from 1995 to 2004, were used to construct a fetal weight standard. We used the Hadlock's fetal growth standard and the proportionality principle to make the standard adjustable for other factors such as race/ethnicity. We validated the standard in different race/ethnicities in the US and against previously published curves from around the world.
  
  
  RESULTS
  The adjustable fetal weight standard has an excellent match with the observed birthweight data in non-Hispanic White, non-Hispanic Black, Hispanics, and Asian from 24 to 38 weeks gestation. It also had a very good fit with cross-sectional data from Australia and Norway, and a longitudinal standard from Brazil. However, our model-based 10th and 90th percentiles differed substantially from studies in Japan and US that used the last menstrual period for estimate of gestational age.
  
  
  CONCLUSIONS
  The adjustable fetal weight standard for twins is a flexible tool and can be used in different populations.
authors.affiliation: MOE-Shanghai Key Laboratory of Children's Environmental Health, Xinhua Hospital, Shanghai Jiao Tong University School of Medicine, 1665 Kong Jiang Road, Shanghai, 200092, China. junjimzhang@gmail.com.|School of Public Health, Guilin Medical College, Guangxi, China. junjimzhang@gmail.com.
authors.forename: Jun
authors.initials: J
authors.lastname: Zhang
authors.affiliation: EMSE - Epidemiological and statistical Methods Research Group, Helmholtz Centre for Infection Research, Braunschweig, Germany. rafael.mikolajczyk@helmholtz-hzi.de.
authors.forename: Rafael
authors.initials: R
authors.lastname: Mikolajczyk
authors.affiliation: MOE-Shanghai Key Laboratory of Children's Environmental Health, Xinhua Hospital, Shanghai Jiao Tong University School of Medicine, 1665 Kong Jiang Road, Shanghai, 200092, China. leixiaopingde@126.com.
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Lei
authors.affiliation: Fetal Medicine Unit & Prenatal Diagnosis Center, Department of Obstetrics, Shanghai First Maternity and Infant Hospital, Tongji University School of Medicine, Shanghai, China. lumings@gmail.com.
authors.forename: Luming
authors.initials: L
authors.lastname: Sun
authors.affiliation: School of Public Health, Guilin Medical College, Guangxi, China. yhp268@163.com.
authors.forename: Hongping
authors.initials: H
authors.lastname: Yu
authors.affiliation: Obstetrics Department, International Peace Maternity & Child Health Hospital, Shanghai Jiaotong University, Shanghai, China. wwcheng29@163.com.
authors.forename: Weiwei
authors.initials: W
authors.lastname: Cheng
mesh_terms: D001724:Birth Weight; D003430:Cross-Sectional Studies; D005260:Female; D047109:Fetal Development; D020567:Fetal Weight; D005865:Gestational Age; D014943:Global Health; D006801:Humans; D007231:Infant, Newborn; D015233:Models, Statistical; D014427:Twins / Q000706:statistics & numerical data*