Relationship between Birth Order and Postnatal Growth until 4 Years of Age: The Japan Environment and Children's Study

Aya Yoshida; Kayo Kaneko; Kohei Aoyama; Naoya Yamaguchi; Atsushi Suzuki; Sayaka Kato; Takeshi Ebara; Mayumi Sugiura-Ogasawara; Michihiro Kamijima; Shinji Saitoh; The Japan Environment And Children's Study Group

doi:10.3390/children10030557

Relationship between Birth Order and Postnatal Growth until 4 Years of Age: The Japan Environment and Children's Study

Children (Basel). 2023 Mar 15;10(3):557. doi: 10.3390/children10030557.

Affiliations

¹ Department of Pediatrics and Neonatology, Graduate School of Medical Sciences, Nagoya City University, Nagoya 4670001, Japan.
² Department of Occupational and Environmental Health, Graduate School of Medical Sciences, Nagoya City University, Nagoya 4670001, Japan.
³ Department of Ergonomics, Institute of Industrial Ecological Sciences, University of Occupational and Environmental Health, Kitakyushu 8078555, Japan.
⁴ Department of Obstetrics and Gynecology, Graduate School of Medical Sciences, Nagoya City University, Nagoya 4670001, Japan.

Abstract

Later-borns tend to be shorter than first-borns in childhood and adulthood. However, large-scale prospective studies examining growth during infancy according to birth order are limited. We aimed to investigate the relationship between birth order and growth during the first 4 years of life in a Japanese prospective birth cohort study. A total of 26,249 full-term singleton births were targeted. General linear and multivariable logistic regression models were performed and adjusted for birth weight, parents' heights, maternal age at delivery, gestational weight gain, maternal smoking and alcohol drinking status during pregnancy, household income, breastfeeding status, and Study Areas. The multivariate adjusted mean length Z-scores in "first-borns having no sibling", "first-borns having siblings", "second-borns", and "third-borns or more" were -0.026, -0.013, 0.136, and 0.120 at birth and -0.324, -0.330, -0.466, and -0.569 at 10 months, respectively. Results similar to those at 10 months were observed at 1.5, 3, and 4 years. The adjusted odds ratios (95% confidence intervals) of short stature at 4 years in "first-borns having siblings", "second-borns", and "third-borns or more" were 1.08 (0.84-1.39), 1.36 (1.13-1.62), and 1.50 (1.20-1.88), respectively, versus "first-borns having no sibling". Birth order was significantly associated with postnatal growth and may be a factor predisposing to short stature in early childhood.

Keywords: birth order; early childhood; height; prospective cohort study; short stature.

Grants and funding

This study was funded by the Ministry of the Environment, Japan. The findings and conclusions of this article are solely the responsibility of the authors and do not represent the official views of the funding authority.