Abstract

Background. The objective was to produce birth weight curves for boys and girls born alive from single pregnancies according to the length of pregnancy and data on infants born in Estonia in 1995–2012. Another purpose was to compare the curves to the birth weight curves found on the basis of data from 1992–1994 and to analyse the factors affecting birth weight according to the data of the Estonian Medical Birth Registry (EMBR).

Methods. Data for the registry-based study were collected from the EMBR. The study included all children born alive from single pregnancies in 1995–2012 in Estonia. A total of 240,108 newborns were analysed. A lineaar regression model was used for describing the correlations between birth weight and sociodemographic conditions. Babies’ birth weights were distributed by gestational age in completed weeks. The 3rd, 10th, 25th, 50th, 75th, 90th and , 97th percentiles were used for birth weight. Birth weight percentiles were calculated according to gestational age in weeks separately for boys and girls. The factors analysed as possibly aff ecting birth weight were mothers’ sociodemographic background, gestational risk factors and previous deliveries/abortions. The factors influencing birth weight were analysed by using an adjusted linear model for regression. The values were presented with a 95% confidence interval. Comparison was made with a birth weight study carried out in 1992–1994.

Results. The number of births according to gestational weeks and birth weight percentiles by boys and girls was presented within gestational weeks 22–43. Birth weight was affected by the baby’s gender, and mother’s education, nationality and marital status. Birth weight was also influenced by previous deliveries, abortions and gestational risk factors. Compared to an earlier study, birth weight decreased at gestational weeks 25–34, by 1–71 g for girls and 9–111 g for boys. Boys’ birth weight at gestational weeks 35–43 increased by 7–140 g and girls’ birth weight at gestational weeks 36–42 increased by 1–70 g.

Conclusions. Comparison of the results of this study and those of a study carried out in Estonia in 1992–1994, allowed to conclude that the birth weight of babies born alive at an earlier gestational age (weeks 22–34) has decreased and the birth weight of babies born at a later gestational age (weeks 35–43) has increased.

Birth weight is aff ected both by sociodemographic aspects and gestational risk factors. Infants’ birth weight needs to be monitored regularly and birth weight curves should be regularly updated in every country.