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Preterm birth varies with season: 25 percent more likely if conception in autumn – Feb 2022

Assessment of Seasonality and Extremely Preterm Birth in Denmark

JAMA Netw Open. 2022;5(2):e2145800. doi:10.1001/jamanetworkopen.2021.45800
Anders Hviid, DrMedSci1,2; Anna Laksafoss, MSc1; Paula Hedley, PhD3; et alUlrik Lausten-Thomsen, PhD4; Henrik Hjalgrim, DrMedSci1,5,6,7; Michael Christiansen, DrMedSci3,7; Sjurdur Frodi Olsen, DrMedSci1

Key Points

  • Question Is seasonality a risk factor associated with extremely preterm birth?
  • Findings In this cohort study of more than 1 million pregnancies involving 662 338 pregnant individuals in Denmark, season during gestation was associated with extremely preterm birth. Gestation during autumn was associated with the highest rate of extremely preterm birth, whereas gestation during winter was associated with the lowest rate.
  • Meaning This study found that season during gestation was associated with extremely preterm birth, suggesting the presence of risk factors associated with seasonality that may be preventable.

Importance Preterm birth, particularly extremely preterm birth, has been associated with substantial morbidity and mortality. Research during SARS-CoV-2–related lockdowns revealed reductions in the more severe subtypes of preterm birth in some countries, suggesting the presence of preventable risk factors, such as infectious diseases or social behavior. Seasonality may provide a similar means of assessing natural changes in the daily life of pregnant individuals that were similar to those experienced during the COVID-19 lockdown period.

Objective To evaluate the association between seasonality and extremely preterm birth.

Design, Setting, and Participants This nationwide cohort study included 1 136 143 pregnancies in Denmark with onset between January 1, 1997, and December 31, 2016, in which the fetuses survived 21 completed weeks of gestation. Pregnancies were followed up until preterm birth, fetal death, or 37 completed weeks of gestation. Data were analyzed from September 2020 to September 2021.

Exposures Season during gestation (primary exposure) and season of pregnancy onset.

Main Outcomes and Measures The main outcome of extremely preterm birth was defined as a live birth occurring between 22 weeks, 0 days’ gestation and 27 weeks, 6 days’ gestation. Cox regression analyses were used to estimate hazard ratios (HRs) for season during gestation and season of pregnancy onset, with adjustment for socioeconomic and demographic factors.

Results Among 662 338 pregnant individuals, the median age at pregnancy onset was 30.0 years (IQR, 6.0 years). Of 1 136 143 pregnancies, 2009 extremely preterm births (cumulative incidence, 0.18%) were identified during follow-up. Season during gestation was associated with extremely preterm birth, with cumulative incidences of 0.17% (95% CI, 0.16%-0.19%) in spring, 0.18% (95% CI, 0.17%-0.20%) in summer, 0.20% (95% CI, 0.18%-0.21%) in autumn, and 0.16% (95% CI, 0.14%-0.17%) in winter.
Compared with winter, the adjusted HRs (AHRs) for the risk of extremely preterm birth were

  • 1.11 (95% CI, 0.97-1.26) for spring,
  • 1.15 (95% CI, 1.02-1.31) for summer, and
  • 1.25 (95% CI, 1.10-1.42) for autumn.

The number of extremely preterm births associated with the increased risk in the spring, summer, and autumn was 56.1 (95% CI, 18.2-99.7), representing 2.8% (95% CI, 0.9%-5.0%) of all extremely preterm births in the study. Season of pregnancy onset was not associated with the risk of extremely preterm birth in spring (AHR, 0.98; 95% CI, 0.95-1.01) or summer (AHR, 1.00; 95% CI, 0.96-1.03) compared with winter, but a slight increase in risk was observed in autumn (AHR, 1.05; 95% CI, 1.02-1.09) compared with winter.

Conclusions and Relevance In this large, national cohort study, seasonality was associated with 2.8% of all extremely preterm births. Season during gestation was associated with the rate of extremely preterm birth, suggesting the presence of potential risk factors associated with season that may be preventable. Further research to identify risk factors for extremely preterm birth associated with seasonality is warranted.
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PRETERM or PREEMIE was in the title of 199 VitaminDWiki pages as of Feb 2022

Fetus development

Details at Ensure a healthy pregnancy and baby - take Vitamin D before conception

VitaminDWiki - Pregnancy problems and Season of Birth

VitaminDWiki – Season of Birth category contains:

Season of birth is a good proxy for Vitamin D (for people far from the Equator)
Statistisically significant, but rarely greater than 20% change
Some health problems need Vitamin D in 2 or 3 trimesters, so are not associated with season
Perhaps some people in born in poor season will need more vitamin D all of their lives

Some Season of Birth studies

# of publications: Life-long health problems associated with Season of Birth


Created by admin. Last Modification: Friday April 19, 2024 23:46:23 GMT-0000 by admin. (Version 9)