title: Birthweight and perinatal mortality among singletons and twins in north-eastern Tanzania.
abstract: BACKGROUND
  Low birthweights as well as high perinatal mortality rates are common in most African populations. Little is known, however, about how low birthweight corresponds with higher mortality rates within African populations. Twins are known to have lower birthweights and higher perinatal mortality rates than singletons. If lower birthweights represent higher perinatal risk per se, small twins within a population with generally lower birthweights should have critically increased risks.
  
  
  METHODS
  In total, 15,255 births in a Tanzanian hospital during 1999-2006 were analysed to determine birthweight distribution and examine perinatal mortality rates (including stillbirths and neonatal deaths within 24 hours) by birthweight in twins and singletons. Referral births from outside the district where the hospital was situated were excluded from analysis.
  
  
  RESULTS
  The mean birthweight for births within an estimated normal distribution was 3,172 g, with a standard deviation of 462 g. The overall perinatal mortality rate was 43.9 per 1,000 births (95% confidence interval: 40.7-47.2). Perinatal mortality rates among twins and singletons were 91.0 and 41.1 per 1000 babies respectively, corresponding to a relative risk of 2.2 (95% confidence interval: 1.7-2.8). The birthweight distribution for twins was shifted to lower birthweights. Twins had a generally lower birthweight and an excess of extremely small births as compared to singletons. The increased mortality rate for twins appeared to be independent of birthweight.
  
  
  CONCLUSIONS
  The two-fold increased risk of perinatal death for twins was observed across the whole birthweight distribution, and very small twins appeared to have an excess perinatal risk that was almost similar to that of larger twins.
authors.affiliation: Department of Public Health and Primary Health Care, University of Bergen, Bergen, Norway. ndema.habib@isf.uib.no
authors.forename: Ndema Abu
authors.initials: NA
authors.lastname: Habib
authors.forename: Anne Kjersti
authors.initials: AK
authors.lastname: Dalveit
authors.forename: Joseph
authors.initials: J
authors.lastname: Mlay
authors.forename: Olola
authors.initials: O
authors.lastname: Oneko
authors.forename: John
authors.initials: J
authors.lastname: Shao
authors.forename: Per
authors.initials: P
authors.lastname: Bergsjø
authors.forename: Erik
authors.initials: E
authors.lastname: Lie-Nielsen
authors.forename: Rolv Terje
authors.initials: RT
authors.lastname: Lie
mesh_terms: D001724:Birth Weight; D003906:Developing Countries; D005260:Female; D006801:Humans; D007226:Infant Mortality; D007231:Infant, Newborn; D011247:Pregnancy; D012042:Registries; D012307:Risk Factors; D012959:Socioeconomic Factors; D050497:Stillbirth / Q000453:epidemiology*; D013636:Tanzania / Q000453:epidemiology; D014427:Twins