title: Differential effects of seasonality on preterm birth and intrauterine growth restriction in rural Africans.
abstract: BACKGROUND
  Low birth weight (LBW) can result from prematurity or intrauterine growth restriction (IUGR) and result in small-for-gestational-age (SGA) infants. Prematurity and IUGR may have different etiologies and consequences.
  
  
  OBJECTIVE
  Our objective was to analyze seasonal patterns of prematurity and SGA in a rural African community and to compare them against variations in nutritional and ecologic variables that may provide insight into likely causative factors.
  
  
  METHODS
  Fourier series were used to compare the seasonality of prematurity (<37 wk) and SGA (<10th percentile of the reference standard) among 1916 live infants born over 26 y in 3 Gambian villages. The resultant patterns were compared against monthly variations in birth frequency, maternal energy status, maternal work, and malaria infections.
  
  
  RESULTS
  The incidence of LBW was 13.3%, of prematurity was 12.3%, and of SGA was 25.1%. Prematurity and SGA showed divergent patterns of seasonality. Incidence of SGA was highest at the end of the annual hungry season, from August to December (peaking in November at 30.6%), with a nadir of 12.9% in June. Rates of SGA varied inversely with maternal weight changes. This pattern was not seen for rates of prematurity, which showed 2 peaks-in July (17.2%) and October (13.9%). The lowest proportion of preterm births occurred in February (5.1%). The peaks in prematurity closely paralleled increases in agricultural labor (July) and malaria infections (October).
  
  
  CONCLUSIONS
  We conclude that a reduction in LBW in such communities may require multiple interventions because of the variety of precipitating factors.
authors.affiliation: MRC Keneba, Medical Research Council Laboratories, The Gambia and the MRC International Nutrition Group, London School of Hygiene and Tropical Medicine, London, UK. pura.solon@lshtm.ac.uk
authors.forename: Pura
authors.initials: P
authors.lastname: Rayco-Solon
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Fulford
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Prentice
mesh_terms: D001724:Birth Weight; D005260:Female; D005714:Gambia / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D007231:Infant, Newborn; D007234:Infant, Premature; D007236:Infant, Small for Gestational Age; D016015:Logistic Models; D011247:Pregnancy; D012424:Rural Population; D012621:Seasons