Birthweights at Term on Rise globally reveals Comprehensive Systematic Review of 183 Million Births

Findings from the review published in the American Journal of Obstetrics and Gynecology revealed a worldwide increase in mean birth weight at term by more than 7 g each year — a total of about 1 lb — since 1950.

"Systematic review of 29 studies showed an increase in term birthweights over time, specifically when considering data since 1950," the researchers wrote. Results remained consistent in several review models.

Giulia Bonanni, Harvard Medical School, Boston, MA, and colleagues aimed to assess global trends in mean birthweights at term, as reported in peer-reviewed literature.

For this purpose, the researchers electronically searched the online databases. There were no restrictions based on language or geographic area. All ecological and observational studies reporting mean birthweight at term as a continuous numerical variable over time were included.

The quality of the included studies was evaluated using the Dufault and Klar checklist modified by Betran et al. The effects of time (years) and geographical origins were also examined. Subgroup analyses focused on national data sources and data collected from 1950 onward.

The researchers reported the following findings:

· Among 6447 reviewed articles, 29 met the criteria, reporting mean birthweight data from over 183 million infants worldwide.

· Most studies were hospital-based (48.3%), 44.8% used national data, and a minority used municipality, community, or regional data (6.9%).

· Geographically, North America (31.0%) had the highest representation, followed by Asia and Europe (27.6% each), and South America and Oceania (6.9% each).

· The univariate linear regression model (Model 1) revealed a significant increase in mean birthweight at term over time (4.74 g/y).

· Model 2, incorporating continental dummy variables into the first model, confirmed this trend (3.85 g/y).

· Model 3, focusing on available national data, did not find a significant relationship.

· Model 4 narrowed its focus on records from 1950 onward, reporting a robust annual increase of 7.26 g/y.

· Model 5, adjusting for the number of participants included in each study, reported a conclusive mean term birthweight increase of 1.46 g/y.

Limitations include study quality variations, data sparsity, and data source diversity, underscoring the need for future research to use precise gestational age distinctions and predetermined time frames to get a deeper understanding of this trend and its implications for child and maternal health.

Reference:

Bonanni G, Airoldi C, Berghella V. Birthweights at term have increased globally: insights from a systematic review of 183 million births. Am J Obstet Gynecol. 2024 Mar 7:S0002-9378(24)00431-9. doi: 10.1016/j.ajog.2024.03.002. Epub ahead of print. PMID: 38460833.