Decline in, and lack of difference between, average birth weights among African and Portuguese babies in Portugal

Background In preliminary data in Portugal, we found that African babies of migrant mothers were heavier than White Portuguese babies born in Lisbon. We investigate whether this pattern is replicated in the national data, and in addition the trends in birth weight in these groups.

Methods Design and setting: Births registered between 1995 and 2002 classified by reported nationality of mothers. Participants: 849 595 Portuguese births ('Portuguese' nationality, predominantly of European descent) and 22 463 African births ('Angola', 'Cape Verde', or 'Guinea Bissau, Republic of Guinea or Equatorial Guinea' nationality, predominantly of African origin).

Results Among Portuguese births, there was a decline in births to teenaged mothers and an increase to mothers aged >= 35 years, with > 9 years of education or in a non-manual class, but among African births there was an increase in births to teenaged mothers and a decline to mothers from advantaged socioeconomic backgrounds. Using the Wilcox-Russell method, overall mean birth weights of term Portuguese (3303, SD 424 g) and African (3297, SD 441 g) babies were not different but the percentage of small preterm births was higher among African (4.7%) than among Portuguese (2.9%) births. Between 1995 and 2002, mean birth weight of term Portuguese babies declined by 58 g (3334-3276 g) and of African babies by 57 g (3341-3284 g). The left shift of the birth weight distributions was independent of maternal age, parity, and social factors among Portuguese babies, but among African babies the decrease appeared to be associated with socioeconomic advantage.

Conclusion There has been a downward trend in birth weights in Portugal among both Portuguese and African term births, but average birth weights of the two groups were similar.