Graphic model of birth weight and gestational age in Monastir, Tunisia

Birth weight for gestational age curves provide to clinicians available references to assess fetal growth in individual infants and in populations. In Tunisia, until now, only North American based references were used. The objective of this study was to create national reference curves for birth weight and to compare these to those actually used in our maternities.

A retrospective population based study was performed over a period of 11 years (from January 1994 to December 2004) using the register of births database of the region of Monastir. We studied a total of 75,751 births. Gestational age of infants ranged from 28 to 43 weeks. Fifth, tenth, 25th, 50th, 75th, 90th and 95th percentiles for weight were calculated by polynomial linear regression of the following general form to construct the clinical curves (Y=a+bX+cX(2)).

The database included 38,646 males and 37,105 females (sex ratio: 1.04). The resulting male and female curves provide smoothed percentiles cutoffs for defining small and large for gestational age births. An actual difference does exist between our curves and those routinely used.

These constructed smoothed gestational curves can be used as a useful tool for assessing birth weight and to evaluate clinical or public health interventions to enhance fetal growth.