Nationwide Trends in Newborn Anthropometric Indicators in Kazakhstan, 2013–2022: A Population-Level Time-Trend Analysis

Background/Objectives: Birth size is a population-level marker of fetal growth, maternal health, and perinatal care. In Kazakhstan, long-term national and regional patterns in newborn anthropometry have not been jointly examined across birth weight, birth length, the Rohrer index, low birth weight (LBW), and macrosomia. This study aimed to quantify national annual trends in these five indicators for 2013–2022, compare region-specific trajectories, and examine whether the two ends of the birth-weight distribution changed in different directions. Methods: This retrospective ecological time-trend study used de-identified individual newborn records (birth weight, birth length, sex, birth date, and region; 3,483,810 live births, 2013–2022) from the Electronic Register of Inpatients of the Ministry of Health of the Republic of Kazakhstan. These individual-level records were used to calculate the Rohrer index and to apply exclusion criteria at the newborn level, but national trend models were deliberately fitted on the 10 annual observations, and regional heterogeneity was tested with a single region × year interaction model rather than individual births or independent per-region regressions to avoid pseudoreplication. Results: Mean birth weight increased from 3429.5 g (2013) to 3518.4 g (2022), and mean birth length increased from 52.5 to 53.3 cm. Recorded LBW prevalence declined from 3.09% to 1.46%, while macrosomia increased from 12.59% to 16.02%. Pooled regional birth weight ranged from 3392.6 g to 3548.6 g, LBW from 0.9% to 5.3%, and macrosomia from 11.7% to 18.1%; region-specific trends after false-discovery-rate correction showed that only North Kazakhstan Region had a statistically robust increase in LBW. Conclusions: Official registry data for Kazakhstan, analyzed at the individual level and aggregated for trend modeling, showed a decade-long increase in mean birth weight and length, an observed decline in recorded LBW prevalence, and an increase in macrosomia prevalence, with statistically confirmed heterogeneity in regional trajectories. Because this study lacked gestational age or maternal characteristics, these findings should be interpreted as ecological surveillance patterns that support continued monitoring of both ends of the birth-weight distribution, rather than as evidence of individual-level changes in fetal growth or maternal metabolic risk.