title: An outcome-based approach for the creation of fetal growth standards: do singletons and twins need separate standards?
abstract: Contemporary fetal growth standards are created by using theoretical properties (percentiles) of birth weight (for gestational age) distributions. The authors used a clinically relevant, outcome-based methodology to determine if separate fetal growth standards are required for singletons and twins. All singleton and twin livebirths between 36 and 42 weeks' gestation in the United States (1995-2002) were included, after exclusions for missing information and other factors (n = 17,811,922). A birth weight range was identified, at each gestational age, over which serious neonatal morbidity and neonatal mortality rates were lowest. Among singleton males at 40 weeks, serious neonatal morbidity/mortality rates were lowest between 3,012 g (95% confidence interval (CI): 3,008, 3,018) and 3,978 g (95% CI: 3,976, 3,980). The low end of this optimal birth weight range for females was 37 g (95% CI: 21, 53) less. The low optimal birth weight was 152 g (95% CI: 121, 183) less for twins compared with singletons. No differences were observed in low optimal birth weight by period (1999-2002 vs. 1995-1998), but small differences were observed for maternal education, race, parity, age, and smoking status. Patterns of birth weight-specific serious neonatal morbidity/neonatal mortality support the need for plurality-specific fetal growth standards.
authors.affiliation: Perinatal Epidemiology Research Unit, Department of Obstetrics and Gynaecology and of Pediatrics, Dalhousie University and the IWK Health Centre, Halifax, Nova Scotia, Canada. ksjoseph@dal.ca
authors.forename: K S
authors.initials: KS
authors.lastname: Joseph
authors.forename: John
authors.initials: J
authors.lastname: Fahey
authors.forename: Robert W
authors.initials: RW
authors.lastname: Platt
authors.forename: Robert M
authors.initials: RM
authors.lastname: Liston
authors.forename: Shoo K
authors.initials: SK
authors.lastname: Lee
authors.forename: Reg
authors.initials: R
authors.lastname: Sauve
authors.forename: Shiliang
authors.initials: S
authors.lastname: Liu
authors.forename: Alexander C
authors.initials: AC
authors.lastname: Allen
authors.forename: Michael S
authors.initials: MS
authors.lastname: Kramer
mesh_terms: D001724:Birth Weight / Q000502:physiology*; D005260:Female; D047109:Fetal Development / Q000502:physiology*; D005865:Gestational Age; D006801:Humans; D007226:Infant Mortality; D007231:Infant, Newborn; D007234:Infant, Premature / Q000502:physiology; D016013:Likelihood Functions; D008297:Male; D017063:Outcome Assessment, Health Care / Q000379:methods*; D011247:Pregnancy; D011256:Pregnancy Outcome / Q000453:epidemiology; D012307:Risk Factors; D017678:Sex Distribution; D014427:Twins / Q000502:physiology*; D014481:United States / Q000453:epidemiology