title: Twin birth weight standards.
abstract: OBJECTIVE
  The aim of this study was to present customized twin-specific birth weight standards. The relative contribution of gestational age, maternal factors, twin factors and placental factors to the birth weight was evaluated in a multivariate approach.
  
  
  METHODS
  Perinatal data were obtained from 10,177 live-born twins from the East Flanders Prospective Twin Survey. Of 8,454 twins (4,227 pairs), of whom all data were available, the birth weights at different gestational ages were analyzed using a non-linear multivariate gaussian regression.
  
  
  RESULTS
  All considered covariates influenced birth weight of twins significantly, with the exception of sex of the co-twin and mode of conception and delivery. At 37 weeks of gestation, a difference of >1 kg existed between favourable and adverse prenatal environment. Up to 40 weeks, sex, site of the umbilical cord, parity, and birth order had a greater influence on birth weight than zygosity, chorionicity and fusion of the placentas. From 34 weeks on, the birth weight of the second-born twin deviated and after 40 weeks, birth weight of monozygotic monochorionic twins dropped, while the other twins continued to grow.
  
  
  CONCLUSIONS
  Customized twin-specific birth weight standards, which take these covariates into account, offer the opportunity for a better assessment of the influence of birth weight of the twin on neonatal health in future research. Already the Developmental Origins of Health and Disease hypothesis showed that these prenatal conditions might also be important for the follow-up of the twin.
authors.affiliation: Nutrition and Toxicology Research Institute Maastricht (NUTRIM), Department of Population Genetics, Genomics and Bioinformatics, Maastricht University, Maastricht, The Netherlands. marij.gielen@gen.unimaas.nl
authors.forename: Marij
authors.initials: M
authors.lastname: Gielen
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Lindsey
authors.forename: Catherine
authors.initials: C
authors.lastname: Derom
authors.forename: Ruth J F
authors.initials: RJ
authors.lastname: Loos
authors.forename: Robert
authors.initials: R
authors.lastname: Derom
authors.forename: Jan G
authors.initials: JG
authors.lastname: Nijhuis
authors.forename: Robert
authors.initials: R
authors.lastname: Vlietinck
mesh_terms: D001724:Birth Weight; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D011446:Prospective Studies; D012015:Reference Standards; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic