Seasonality updated in 28 European/Mediterranean countries: A continuing enigma

Cummings, David R.

doi:10.1002/ajhb.22534

Cited by 5 publications

(3 citation statements)

References 10 publications

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“…Human birth seasonality is a common phenomenon in most populations ( 65 , 66 ). In Brazil, peaks in births are observed between March and May, with a secondary peak in September ( 52 ).…”

Section: Methodsmentioning

confidence: 99%

Implications of Zika virus and congenital Zika syndrome for the number of live births in Brazil

Castro

Han

Carvalho

et al. 2018

Proc. Natl. Acad. Sci. U.S.A.

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SignificanceZika virus (ZIKV) was discovered 70 years ago, and since then small isolated outbreaks occurred without major complications being reported. When ZIKV hit Brazil, however, a public health emergency was declared, given its link with microcephaly. Knowledge on ZIKV has advanced, but demographic impacts remain poorly understood. This study uses data from Brazil to assess whether a decline in births occurred after the onset of ZIKV. Forecasts show significant birth declines, particularly after April 2016. No significant changes in fetal death rates and no pattern of increase in hospitalizations due to abortion complications were observed, although hospitalizations occurred later in some states. We argue that postponement of pregnancy and abortions, primarily, likely affected fertility, with implications for women’s reproductive health.

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“…Human birth seasonality is a common phenomenon in most populations ( 65 , 66 ). In Brazil, peaks in births are observed between March and May, with a secondary peak in September ( 52 ).…”

Section: Methodsmentioning

confidence: 99%

Implications of Zika virus and congenital Zika syndrome for the number of live births in Brazil

Castro

Han

Carvalho

et al. 2018

Proc. Natl. Acad. Sci. U.S.A.

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“…Another key aspect in birth patterns in Brazil is a set of two well-documented peaks, in March-May and in September, with no significant seasonal variation across educational levels or regions (Moreira 2013). Seasonality in births is commonly reported in all human populations, and the pattern is resistant to change over time (Cummings 2014), suggesting the need to account for context-specific seasonality.…”

Section: Live Births and Fertility In Brazilmentioning

confidence: 99%

Live Births and Fertility Amid the Zika Epidemic in Brazil

et al. 2020

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In late 2015, the Brazilian Ministry of Health and the Pan American Health Organization classified the increase in congenital malformations associated with the Zika virus (ZIKV) as a public health emergency. The risk of ZIKV-related congenital syndrome poses a threat to reproductive outcomes that could result in declining numbers of live births and potentially fertility. Using monthly microdata on live births from the Brazilian Information System on Live Births (SINASC), this study examines live births and fertility trends amid the ZIKV epidemic in Brazil. Findings suggest a decline in live births that is stratified across educational and geographic lines, beginning approximately nine months after the link between ZIKV and microcephaly was publicly announced. Although declines in total fertility rates were small, fertility trends estimated by age and maternal education suggest important differences in how Zika might have impacted Brazil’s fertility structure. Further findings confirm the significant declines in live births in mid-2016 even when characteristics of the municipality are controlled for; these results highlight important nuances in the timing and magnitude of the decline. Combined, our findings illustrate the value of understanding how the risk of a health threat directed at fetuses has led to declines in live births and fertility.

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“…Seasonal variations in human natural conception and birth rates have been demonstrated by several studies ( James, 1990 ; Rojansky et al , 1992 ; Lam and Miron, 1994 ; Cummings, 2014 ; Wesselink et al , 2020 ). It has been hypothesized that natural conception is affected by biological factors, such as environmental temperature and light exposure, which possibly affect sperm quality, melatonin secretion and vitamin D synthesis, all important parameters for the reproductive efficacy ( Kauppila et al , 1987 ; Lam and Miron, 1991 ; Rojansky et al , 1992 ; Reiter, 1993 ; Levine, 1994 ; Bronson, 1995 ; Levine, 1999 ; Cummings, 2003 , 2007 , 2010a , b ; Reiter et al , 2014 ; Blomberg Jensen et al , 2018 ).…”

Section: Introductionmentioning

confidence: 94%

Summer is not associated with higher live birth rates in fresh IVF/ICSI cycles: a population-based nationwide registry study

Humla

Bergh

Akouri

2022

Human Reproduction Open

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STUDY QUESTION Is summer associated with higher live birth rate after fresh IVF/ICSI? SUMMARY ANSWER There was no support for a higher live birth rate after fresh IVF/ICSI when treatment was performed during the summer season. WHAT IS KNOWN ALREADY Seasonal variations in human natural conception and birth rates are well described. It has been hypothesized that serum vitamin D, levels of which are associated with sun exposure, may have a role in human natural conception rates. However, the association between seasons and IVF outcomes has not yet been clarified and conflicting reports have been published. Furthermore, it has been suggested that women with normal vitamin D levels have a better pregnancy outcome after ART compared to those with vitamin D insufficiency. STUDY DESIGN, SIZE, DURATION A nationwide, register-based cohort study including all first time fresh IVF/ICSI treatments (n = 52 788) leading to oocyte retrieval in Sweden between 2009 and 2018 was carried out. PARTICIPANTS/MATERIALS, SETTING, METHODS All first time fresh IVF/ICSI cycles leading to oocyte retrieval were identified in the National Quality Registry of Assisted Reproduction. Data collected included patient characteristics as well as information about the treatment cycle and pregnancy outcome. The patients were divided into season subgroups, (summer, autumn, winter and spring) based on the date of oocyte retrieval. The primary outcome was live birth rate, which was defined as the number of live births per oocyte retrieval and embryo transfer (ET). Other outcomes included clinical pregnancy per ET and miscarriage per clinical pregnancy. Logistic regression with multiple imputation was performed to evaluate whether there was an association between season and IVF/ICSI outcomes, with summer as reference. Adjustments were made for woman’s age, year of treatment, BMI, total FSH/hMG dose, type of treatment, fertilization type, embryonic stage at ET and number of embryos transferred. MAIN RESULTS AND THE ROLE OF CHANCE Live birth rate per oocyte retrieval ranged between 24% and 26% among seasons. A significantly higher live birth rate was seen for spring compared with summer, 26% versus 24%, respectively (adjusted OR 1.08, 95% CI 1.02-1.16, p=0.02). No significant association was seen when winter and autumn were compared with summer. Live birth rate per ET ranged between 29% and 31% among seasons. A significantly higher live birth rate was seen for spring and autumn compared with summer, at 31% and 31% respectively versus 29% (adjusted OR 1.08, 95% CI 1.01-1.16, p=0.04 and adjusted OR 1.09, 95% CI 1.01-1.16, p=0.02) respectively. No significant association was seen when winter was compared with summer. Clinical pregnancy rate varied between 36% and 38% and miscarriage rate between 16% and 18%, with no significant seasonal associations. LIMITATIONS, REASONS FOR CAUTION Possible limitations are the retrospective design of the study and unmeasured confounders. Another limitation is that a generalized estimating equation (GEE) model was not used. The use of a GEE model would have made it possible to include all started fresh IVF/ICSI cycles since it allows for correction for any dependence between cycles within women. WIDER IMPLICATIONS OF THE FINDINGS The results of this large registry study give no support for the hypothesis that IVF/ICSI treatments performed during summer season, with the highest degree of sunlight and vitamin D synthesis, is associated with higher pregnancy and live birth rates. In fact, our results showed significantly lower live birth rates during summer compared with spring and autumn. However, the magnitude of this difference was small and unlikely of clinical value. We suggest that season should not be taken into consideration when planning and performing fresh IVF/ICSI treatments. STUDY FUNDING/COMPETING INTEREST(S) Financial support was received through the Swedish state under the agreement between the Swedish government and the county councils, the ALF-agreement (ALFGBG-70 940) and grants from the Hjalmar Svensson's Research Foundation (Grant Nr. HJSV2021019 and HJSV2021037). None of the authors declare any conflict of interest. TRIAL REGISTRATION NUMBER N/A

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Seasonality updated in 28 European/Mediterranean countries: A continuing enigma

Cited by 5 publications

References 10 publications

Implications of Zika virus and congenital Zika syndrome for the number of live births in Brazil

Implications of Zika virus and congenital Zika syndrome for the number of live births in Brazil

Live Births and Fertility Amid the Zika Epidemic in Brazil

Summer is not associated with higher live birth rates in fresh IVF/ICSI cycles: a population-based nationwide registry study

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