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Am J Perinatol 2021; 38(07): 683-689
DOI: 10.1055/s-0039-3400449
Original Article

Male-to-Female Ratios, Race/Ethnicity, and Spontaneous Preterm Birth among 11 Million California Infants

Gary M. Shaw 
1   March of Dimes Prematurity Research Center at Stanford University, Division of Neonatal and Developmental Medicine, Department of Pediatrics, Stanford University School of Medicine, Stanford, California
,
Jonathan A. Mayo
1   March of Dimes Prematurity Research Center at Stanford University, Division of Neonatal and Developmental Medicine, Department of Pediatrics, Stanford University School of Medicine, Stanford, California
,
Michael L. Eisenberg
2   Department of Urology, Stanford University School of Medicine, Stanford, California
,
Ralph Catalano
3   School of Public Health, University of California, Berkeley, Berkeley, California
,
David K. Stevenson
1   March of Dimes Prematurity Research Center at Stanford University, Division of Neonatal and Developmental Medicine, Department of Pediatrics, Stanford University School of Medicine, Stanford, California
› Author Affiliations Funding This project was supported by the March of Dimes Prematurity Research Center at Stanford University (MOD PR625253).
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Abstract

Objective An observed disparity in population-scale data are a larger number of males among preterm births (PTBs). We investigated spontaneous PTB risk among women of various race/ethnic groups in combination with infants' sex.

Study Design This observational study was conducted in > 10 million California births (1991–2012) using birth certificates linked with maternal and infant hospital discharge data.

Results Male-to-female ratios among term (37–42 weeks) infants exhibited the narrow ratio range 1.02 to 1.06 across race/ethnic groups. Such ratios among spontaneous PTBs were generally larger for all race/ethnic groups except non-Hispanic blacks. For blacks, ratios tended to be lower and similar to their term birth counterpart, 1.03. Hazard ratios adjusted for maternal age and education for non-Hispanic blacks were 0.99 (95% confidence interval [CI] 0.90–1.09), 1.01 (95% CI 0.95–1.08), 0.98 (95% CI 0.94–1.03), and 1.03 (95% CI 1.01–1.05), respectively, for gestational week groupings of 20 to 23, 24 to 27, 28 to 321, and 32 to 36. Hazard ratios for non-Hispanic whites for the same groupings were 1.08 (95% CI 0.98–1.18), 1.13 (95% CI 1.07–1.19), 1.21 (95% CI 1.17–1.25), and 1.18 (95% CI 1.17–1.19).

Conclusion Why male-to-female ratios are similar across gestational ages in blacks but substantially higher in other race/ethnic groups is theoretically considered relative to inflammation, stress, and other influences.

Keywords

secondary sex ratio - disparity - prematurity - pregnancy

Note

The data are publicly available from the Office of Statewide Health Planning and Development (OSHPD). The data are not available for replication because specific approvals from OSHPD and the California Committee for the Protection of Human Subjects must be obtained to access them.


Supplementary Material



Publication History

Received: 11 July 2019

Accepted: 14 October 2019

Article published online:
22 November 2019

© 2019. Thieme. All rights reserved.

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