title: First birth interval, an indicator of energetic status, is a predictor of lifetime reproductive strategy.
abstract: OBJECTIVE
  Women should differ in their reproductive strategies according to their nutritional status. We tested a hypothesis that women who have a good nutritional status early in life, as indicated by a shorter waiting time to the first birth (first birth interval, FBI), are able to afford higher costs of reproduction than women who have worse nutritional condition.
  
  
  METHODS
  We collected data on 377 women who got married between the years 1782 and 1882 in a natural fertility population in rural Poland. The study group was divided into tertiles based on the length of FBI.
  
  
  RESULTS
  Women with the shortest FBI had a higher number of children (P = 0.005), higher number of sons (P = 0.01), and shorter mean interbirth intervals (P = 0.06). Women who had ever given birth to twins had shorter FBI than women of singletons (20.1 and 26.1 months, respectively; P = 0.049). Furthermore, women with a shorter FBI, despite having higher costs of reproduction, did not have a different lifespan than women with a longer FBI.
  
  
  CONCLUSIONS
  Our results suggest that women who were in better energetic condition (shorter length of FBI), achieved higher reproductive success without reduction in lifespan. FBI reflects interindividual variation, which may result from variation in nutritional status early in life and thus may be a good predictor of subsequent reproductive strategy. We propose to use FBI as an indicator of women's nutritional status in studies of historical populations, especially when information about social status is not available.
authors.affiliation: Department of Environmental Health, Institute of Public Health, Jagiellonian University Medical College, Grzegorzecka 20, Krakow 31-351, Poland. ilona.nenko@uj.edu.pl
authors.forename: Ilona
authors.initials: I
authors.lastname: Nenko
authors.forename: Grazyna
authors.initials: G
authors.lastname: Jasienska
mesh_terms: D000704:Analysis of Variance; D001721:Birth Intervals / Q000706:statistics & numerical data*; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D007231:Infant, Newborn; D008136:Longevity; D008297:Male; D015999:Multivariate Analysis; D009752:Nutritional Status; D010298:Parity; D011044:Poland; D011247:Pregnancy; D059285:Pregnancy, Twin / Q000706:statistics & numerical data*; D012189:Retrospective Studies; D012424:Rural Population / Q000706:statistics & numerical data; D013997:Time Factors