Customised birthweight standard for a Slovenian population.

Objective To produce a customised birthweight standard for Slovenia. Methods This retrospective study used a cohort from the National Perinatal Information System of Slovenia (NPIS). Prospectively collected information from pregnancies delivered in all of Slovenia's 14 maternal hospitals between 1st January 2003 and 31st December 2012 was included. Coefficients were derived using a backward stepwise multiple regression technique. Results A total of 126,627 consecutive deliveries with complete data were included in the multivariable analysis. Maternal height, weight in early pregnancy and parity as well as the baby's sex were identified as physiological variables, with coefficients comparable to findings in other countries. The expected 280-day birthweight, free from pathological influences, of a standard size mother (height 163 cm, weight 64 kg) in her first pregnancy was 3451.3 g. Pathological influences on birthweight within this population included low and high maternal age, low and high body mass index (BMI), smoking, pre-existing and gestational diabetes and pre-existing and gestational hypertension. Conclusion The analysis confirmed the main physiological variables that affect birthweight in studies from other countries, and was able to quantify additional pathological factors of maternal age and gestational diabetes. Development of a country-specific customised birthweight standard will aid clinicians in Slovenia with the distinction between normal and abnormal small-for-gestational age (SGA) fetuses, thus avoiding unnecessary interventions and improving identification of at risk pregnancies, and long-term outcomes for infants.