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
- Preterm birth varies with season: 25 percent more likely if conception in autumn – Feb 2022
- Little sun in first trimester, 2.9 X more likely to have learning disabilities – June 2019
- Conception in winter increases rate of Autism, learning disabilities, dyslexia – Oct 2016
- UV at time of conception associated with Vitamin D Receptor activation 65 years later – Sept 2017
- Autoimmune Addison's Disease – increased risk if born in Dec or Jan – Nov 2016
- Health problems are related to birth month - June 2015
- Schizophrenia increased 40 percent for Spring births after Danes stopped vitamin D fortification – April 2014
- Season of birth associated with Pneumonia (10 %) and Multiple Sclerosis (30 %) – May 2013
- Multiple Sclerosis 23 percent more likely if born in April vs. Oct – meta-analysis Nov 2012
- Association between season of birth and suicide – perhaps vitamin D – Sept 2012
- 7 percent less likely to get immune mediated disease if born in the fall – July 2012
- Odds of living to 100 increase by 40 percent if had been born in the fall – 2011
- Diseases correlated to month of birth – 2008
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
- Season of birth associated with many health problem (UK Biobank) – Nov 2020
- Preterm birth varies with season: 25 percent more likely if conception in autumn – Feb 2022
- Little sun in first trimester, 2.9 X more likely to have learning disabilities – June 2019
- UV at time of conception associated with Vitamin D Receptor activation 65 years later – Sept 2017
- Autoimmune Addison's Disease – increased risk if born in Dec or Jan – Nov 2016
- Schizophrenia increased 40 percent for Spring births after Danes stopped vitamin D fortification – April 2014
- Season of birth associated with Pneumonia (10 %) and Multiple Sclerosis (30 %) – May 2013
- Majority of Season of Birth health problems should vanish if take Vitamin D
100K monthly, or 50K bi-weekly, or 4K daily
# of publications: Life-long health problems associated with Season of Birth