Secular trend in birthweight among the Purari delta population, Papua New Guinea

The aim of this analysis was to examine the extent and possible seasonal nature of the secular trend in mean birthweight in the Purari delta, Papua New Guinea. This is a country undergoing rapid modernization, and with this has come a secular trend toward increased adult body size in some parts of the country but not others. Birthweight data, collected by month of delivery at Kapuna Hospital in the Purari delta between the years 1969 and 1996, was analysed by year of birth and by season, using one-way analysis of variance and post hoc Scheffé tests with the statistical software SPSS-PC+. A total of 927 birthweights for the years 1969, 1972, 1977, 1994 and 1996 were included in the analysis. Twin births were excluded from analysis, as were births below 1.5 kg. There is clear evidence of a secular trend in increasing mean birthweight between the period 1969 and 1996, with the largest significant difference being between 1977 and 1994, from 2.70 to 2.92 kg. There were no significant differences in mean birthweight between the sexes. The rate of birthweight increase between 1977 and 1994 was 130 g per decade, lower than the gain of 200 g per decade in the period 1994-1996. The decline in birthweight of 90 g per decade during the period 1969-1977 is not statistically significant. The proportion of infants born with low birth weight (< 2.5 kg) shows an increase between 1969 and 1972, and a decline thereafter. While seasonal differences in birthweight during any of the years examined is non-significant, significantly greater mean birthweight across the period 1969-1996 was found for births during the wet season (April to July), and the drier season (August to November), respectively. The secular increase in mean birthweight is likely to be a consequence of the improvements in maternal diet and increased maternal body size that have come with economic modernization. The secular trend of seasonality in mean birthweight among the Purari delta population may be a function of seasonally varied displacement of traditional diet by non-local bought foods, as well as reduced seasonality of maternal workload associated with the processing of the traditional staple food.