title: Birth weight centiles by gestational age for twins born in south India.
abstract: BACKGROUND
  Birth weight centile curves are commonly used as a screening tool and to assess the position of a newborn on a given reference distribution. Birth weight of twins are known to be less than those of comparable singletons and twin-specific birth weight centile curves are recommended for use. In this study, we aim to construct gestational age specific birth weight centile curves for twins born in south India.
  
  
  METHODS
  The study was conducted at the Christian Medical College, Vellore, south India. The birth records of all consecutive pregnancies resulting in twin births between 1991 and 2005 were reviewed. Only live twin births between 24 and 42 weeks of gestation were included. Birth weight centiles for gestational age were obtained using the methodology of generalized additive models for location, scale and shape (GAMLSS). Centiles curves were obtained separately for monochorionic and dichorionic twins.
  
  
  RESULTS
  Of 1530 twin pregnancies delivered during the study period (1991-2005), 1304 were included in the analysis. The median gestational age at birth was 36 weeks (1st quartile 34, 3rd quartile 38 weeks). Smoothed percentile curves for birth weight by gestational age increased progressively till 38 weeks and levels off thereafter. Compared with dichorionic twins, monochorionic twins had lower birth weight for gestational age from after 27 weeks.
  
  
  CONCLUSIONS
  We provide centile values of birth weight at 24 to 42 completed weeks of gestation for twins born in south India. These charts could be used both in routine clinical assessments and epidemiological studies.
authors.affiliation: Departments of Biostatistics, Christian Medical College, Vellore, 632 002, India. prasanna.samuel@cmcvellore.ac.in.
authors.forename: Prasanna
authors.initials: P
authors.lastname: Premkumar
authors.affiliation: Departments of Biostatistics, Christian Medical College, Vellore, 632 002, India.
authors.forename: Belavendra
authors.initials: B
authors.lastname: Antonisamy
authors.affiliation: Obstetrics and Gynaecology, Christian Medical College, Vellore, 632 002, India.
authors.forename: Jiji
authors.initials: J
authors.lastname: Mathews
authors.affiliation: Obstetrics and Gynaecology, Christian Medical College, Vellore, 632 002, India.
authors.forename: Santhosh
authors.initials: S
authors.lastname: Benjamin
authors.affiliation: Obstetrics and Gynaecology, Christian Medical College, Vellore, 632 002, India.
authors.forename: Annie
authors.initials: A
authors.lastname: Regi
authors.affiliation: Obstetrics and Gynaecology, Christian Medical College, Vellore, 632 002, India.
authors.forename: Ruby
authors.initials: R
authors.lastname: Jose
authors.affiliation: Neonatology, Christian Medical College, Vellore, 632 002, India.
authors.forename: Anil
authors.initials: A
authors.lastname: Kuruvilla
authors.affiliation: Making Pregnancy Safer Department, World Health Organization, Geneva, Switzerland.
authors.forename: Mathews
authors.initials: M
authors.lastname: Mathai
mesh_terms: D001719:Birth Certificates; D001724:Birth Weight; D005260:Female; D005865:Gestational Age; D057238:Growth Charts; D006801:Humans; D007194:India; D007231:Infant, Newborn; D008297:Male; D012016:Reference Values; D014427:Twins / Q000706:statistics & numerical data*
keywords: Birth weight; Centiles; GAMLSS; Gestational age; India; Twins