Research pointers: Unexplained differences in sex ratios at birth in Europe and North America

Trend Analysis of the Sex Ratio at Birth in Greece

INTRODUCTION

The sex ratio at birth, defined as the ratio of male to female live births, is a key indicator in the study of human reproduction and demographic patterns. This study aims to systematically examine the sex ratio in Greece and analyze its temporal trends over the period from 1956 to 2023.

MATERIALS AND METHODS

Data on the total number of live births in Greece, categorized by sex, were obtained from the Hellenic Statistical Authority based on birth certificate records. The sex ratio for each year was calculated as the number of male births per 1,000 female births. Trend analysis was conducted using joinpoint regression and supplemented with linear regression. The annual percent change (APC) and the beta coefficient were computed, along with 95% confidence intervals (95% CIs).

RESULTS

Between 1956 and 2023, a total of 8,215,934 live births were recorded in Greece. The overall sex ratio at birth across all years was 1,068 male births per 1,000 female births, resulting in 269,468 excess male neonates. The gender ratio at birth ranged from a low of 1,047 in 1996 to a high of 1,085 in 2001. In all reported years, the sex ratio at birth was above 1,050, except for 1996. In the most recent year, 2023, the male-to-female ratio at birth was the second lowest of the entire period, at 1,051. Trend analysis revealed that the sex ratio at birth remained stable from 1956 to 1982 (p = 0.862) and showed a statistically significant downward trend from 1982 to 2023, with an annual percent change of -0.0274 (p = 0.004), or an average annual decrease of -0.297 (95% CI: -0.504 to -0.090, p = 0.006) male births per 1,000 female births.

CONCLUSIONS

The sex ratio at birth in Greece has significantly declined over the past four decades, reflecting similar trends observed in other developed nations. Further research is required to investigate the complex biological, demographic, and social factors influencing these trends, providing deeper insight into key aspects of human reproduction.

Gender inequality in workloads explained by operational sex ratio

Ecological differences between human populations can affect the relative strength of sexual selection, and hence drive gender inequality. Here, we exploit the cultural diversity of southwestern China, where some village sex ratios are female-biased, in part due to a proportion of males entering monastic celibacy, to evaluate the role of sex ratio on the sexual division of labor. We used a detachable activity tracker to measure workload by step counts in both sexes among 561 individuals in 55 villages in six different areas. We show that a lower sex ratio and a higher prevalence of monasticism are associated with higher women's workloads and reduced men's workloads in the non-celibate population. As the operational sex ratio increases, gender inequality diminishes. This study offers valuable insights into the origins of gender disparities by examining the role of sex ratio on the sexual division of labor.

Ambient temperature-related sex ratio at birth in historical urban populations: the example of the city of Poznań, 1848-1900

This study examines whether exposure to ambient temperature in nineteenth-century urban space affected the ratio of boys to girls at birth. Furthermore, we investigate the details of temperature effects timing upon sex ratio at birth. The research included 66,009 individual births, aggregated in subsequent months of births for the years 1847-1900, i.e. 33,922 boys and 32,087 girls. The statistical modelling of the probability of a girl being born is based on logistic GAM with penalized splines and automatically selected complexity. Our research emphasizes the significant effect of temperature in the year of conception: the higher the temperature was, the smaller probability of a girl being born was observed. There were also several significant temperature lags before conception and during pregnancy. Our findings indicate that in the past, ambient temperature, similar to psychological stress, hunger, malnutrition, and social and economic factors, influenced the viability of a foetus. Research on the effects of climate on the sex ratio in historical populations may allow for a better understanding of the relationship between environmental factors and reproduction, especially concerning historical populations since due to some cultural limitations, they were more prone to stronger environmental stressors than currently.

Divergences in sex ratio at birth in US Census Regions due to racial factors: chronic stress and female foeticide

OBJECTIVES

The sex ratio of live births (males/total [M/T]) approximates 0.515. Many factors reduce M/T, and these include stress. Antenatal sexing is used for female foeticide in the setting of male offspring preference. Regional differences and latitude gradients in M/T also occur. This study analysed M/T in the US by Census Regions.

STUDY DESIGN

This was an ecological study.

METHODS

Live births by sex, Census region, state and mother's race were obtained from CDC Wonder (2007-2020).

RESULTS

There were 55,453,437 births (M/T 0.5116, 95% confidence interval: 0.5115-0.5118). M/T was Black/African American < Indian/Alaska Native American < White < Asian (P<<0.0001). M/T was significantly lowest in South and highest in West. The South had the lowest proportion of Asian/Pacific Islander births (3.9%) and the highest proportion of Black/African American (21.9%). West has the highest proportion of Asian/Pacific Islander (11.2%) and the lowest proportion of Black/African American births (5.3%). In Asian/Pacific Islander births, M/T significantly rose to third order and fell to sixth order births, unlike the other races that showed a decline from the first order.

CONCLUSIONS

Asian M/T may be elevated because of male offspring preference and selective female foeticide. M/T may be depressed in Black and American Indian/Alaskan births due to chronic stress, as race remains the most important factor associated with wealth inequality in the United States. The lower M/T of these two races when compared with White equates to a constant loss of 4.13 and 2.55/1000 male births. The higher Asian M implies a chronic loss of 3.78 females per 1000 births. Both have public health implications.

Different COVID-19 treatments' impact on hospital length of stay

IMPORTANCE

COVID-19 has adversely affected global healthcare infrastructure since 2019. Currently, there are no large-scale published reports on the efficacy of combination therapy of dexamethasone, remdesivir, and tocilizumab on COVID-19 patients.

OBJECTIVES

Is the combination therapy of dexamethasone, remdesivir, and tocilizumab superior to other treatments on hospitalized COVID-19 patients?

DESIGN

This is a retrospective, comparative effectiveness study.

SETTING

Single-center study PARTICIPANTS/INTERVENTIONS: We analyzed different inpatient COVID-19 treatment options available in the United States and their impact on hospital length of stay (LOS) and mortality. Hospitalized COVID-19 were categorized as "mild," "moderate" and "severe'' based on the highest level of oxygen required; room air, nasal cannula, or high flow/PAP/intubation, respectively. Patients were treated in accordance with the availability of medications and the latest treatment guidelines.

MAIN OUTCOMES

The endpoints of the study are hospital discharges and death during hospitalization.

RESULTS

1233 COVID-19 patients were admitted from 2020 to 2021. No treatment combinations showed a statistically significant decrease in hospital LOS in mild COVID-19 patients (p = 0.186). In moderate patients, the combination of remdesivir and dexamethasone slightly decreased LOS by 1 day (p = 0.007). In severe patients, the three-drug combination of remdesivir, dexamethasone, and tocilizumab decreased LOS by 8 days (p = 0.0034) when compared to nonviable treatments, such as hydroxychloroquine and convalescent plasma transfusion. However, it did not show any statistically significant benefit when compared to two-drug regimens (dexamethasone plus remdesivir) in severe COVID-19 (p = 0.116). No treatment arm appeared to show a statistically significant decrease in mortality for severe COVID-19 patients.

CONCLUSIONS

Our findings suggest that three-drug combination may decrease LOS in severe COVID-19 patients when compared to two-drug therapy. However, the trend was not supported by statistical analysis. Remdesivir may not be clinically beneficial for mild hospitalized COVID-19 patients; considering its cost, one could reserve it for moderate and severe patients. Triple drug therapies, while potentially reducing LOS for severe patients, do not affect overall mortality. Additional patient data may increase statistical power and solidify these findings.

Life history traits of Mystus vittatus in the Ganges River, Bangladesh: recommendation for its sustainable management considering climate change

Freshwater catfishes are regarded primarily as a source of food and sport, so they are highly valuable economically. We comprehensively studied life history features of Mystus vittatus, including sex ratio (SR), population structure, growth pattern, condition, form factor (a_3.0), sexual maturity (L_m), spawning season, fecundity, mortality (i.e., total mortality (Z), natural-mortality (M_W), and fishing mortality (F)), optimum catchable length (L_opt), length at first capture (L_c), and environmental factors (temperature and rainfall) with management policies from the Ganges River during July 2017 to June 2018. SR (1:1.48) differed noticeably from the expected 1:1 ratio (p < 0.05). Total length (TL) ranged from 6.80-16.00 cm for males and 6.53-18.80 cm for females. The growth was negative allometric for both sexes. Fulton's condition factor was the best one and mean relative weight showed no significant difference from 100 for both sexes that indicates balanced population. L_m was 9.60, 9.70, and 8.80 cm based on the gonadosomatic index (GSI), logistic, and maximum length (L_max), respectively. Spawning season was April to September and the peak was May to July. Fecundity varied from 5942 to 49,852 (mean ± SD, 11,898 ± 5028) and a positively correlated with TL and BW. Z was 1.80 year^-1, M_w was 0.97 year^-1, and F was 0.83 year^-1. L_opt was 11.14 cm (TL) and L_c was ~ 8.47 cm (TL). Temperature and rainfall both were significantly related with GSI and suitable range of temperature and rainfall for spawning of M. vittatus was 28-34 °C and 200-390 mm, respectively. Long data series pointed that average air temperature was increasing and rainfall was decreasing. By considering all of the above parameters, we can take the proper management actions for M. vittatus and other freshwater catfishes on the Indian sub-continent, to ensure long-term self-sustainability and sustainable harvest for the benefit of fishers and communities.

Sex differences in surgically correctable congenital anomalies: A systematic review

PURPOSE

This study aims to compare the prevalence and outcomes of surgically correctable congenital anomalies between sexes.

METHODS

Upon registration on PROSPERO (CRD42019120165), a librarian aided in conducting a systematic review using PRISMA guidelines. The five largest relevant studies were included for each anomaly. Cumulative prevalence differences and confidence intervals were calculated, and the Cochran-Mantel-Haenszel test was performed.

RESULTS

Of 42,722 identified studies, 68 were included in our analysis. All included anomalies had greater than 1000 patients except duodenal atresia (n = 787) and intestinal duplication (n = 148). Males had a significantly higher prevalence than females in 10/14 anomalies (Hirschsprung's disease, omphalomesenteric duct, congenital diaphragmatic hernia, anorectal malformation, malrotation, esophageal atresia, congenital pulmonary airway malformation, intestinal atresia, omphalocele, and gastroschisis; p < 0.001). There was no difference in the prevalence of duodenal atresia or intestinal duplication between sexes (p = 0.88 and 0.65, respectively). Females had a significantly higher prevalence of biliary anomalies (atresia and choledochal cyst).

CONCLUSION

Our study indicates that males have higher prevalence rates of most congenital anomalies. Further investigations are required to illuminate the embryology underlying this sex distribution and whether sex influences outcomes.

TYPE OF STUDY

Systematic review and meta-analysis.

LEVEL OF EVIDENCE

Prognostic study, level II.

Estimating birth weight from observed postnatal weights in a Guatemalan highland community

OBJECTIVE

Low birth weight is one of the leading contributors to global perinatal deaths. Detecting this problem close to birth enables the initiation of early intervention, thus reducing the long-term impact on the fetus. However, in low-and middle-income countries, sometimes newborns are weighted days or months after birth, thus challenging the identification of low birth weight. This study aims to estimate birth weight from observed postnatal weights recorded in a Guatemalan highland community.

APPROACH

With 918 newborns recorded in postpartum visits at a Guatemalan highland community, we fitted traditional infant weight models (Count's and Reeds models). The model that fitted the observed data best was selected based on typical newborn weight patterns reported in the medical literature and previous longitudinal studies. Then, estimated birth weights were determined using the weight gain percentage derived from the fitted weight curve.

MAIN RESULTS

The best model for both genders was the Reeds2 model, with a mean square error of 0.30 kg2 and 0.23 kg2 for male and female newborns, respectively. The fitted weight curves exhibited similar behavior to those reported in the literature, with a maximum weight loss around three to five days after birth, and birth weight recovery, on average, by day ten. Moreover, the estimated birth weight was consistent with the 2015 Guatemalan National Survey, no having a statistically significant difference between the estimated birth weight and the reported survey birth weights (two-sided Wilcoxon rank-sum test; [Formula: see text]).

SIGNIFICANCE

By estimating birth weight at an opportune time, several days after birth, it may be possible to identify low birth weight more accurately, thus providing timely treatment when is required.

A systematic search of the factors that influence the sex ratio at birth

INTRODUCTION

The sex ratio at birth has been studied for decades. A systematic review of the factors that influence this has never been performed. This study conducted a systematic search of this topic.

METHODS

A scoping review of the literature was initially carried out in January 2012 and this was formally updated for contemporaneity in December 2017. A systematic search of the literature subsequently followed in May 2019 and was conducted based on PRISMA statement's flow diagram. The search was applied across five databases: Cumulative Index to Nursing and Allied Health Literature (CINAHL), MEDLINE, PubMed, The Cochrane Library and Web of Science and was restricted to January 1, 1990 to May 31, 2019. The systematic review stopped at screening stage of the PRISMA. A narrative approach was adopted to report study findings.

RESULTS

494 studies were included. Ten factors were identified from the literature as having an influence on M/F, with stress and sex-selective termination being the most predominant. Additional factors included the hormonal theory, geographical trends, coital rates, radiation, secular trends, seasonality and theoretical modeling.

DISCUSSION

Future studies addressing M/F should adopt similar methodologies in order to provide the possibility of comparison between findings and a more formal form of systematic review.

Secondary sex ratio in assisted reproduction: an analysis of 1 376 454 treatment cycles performed in the UK

STUDY QUESTION

Does ART impact the secondary sex ratio (SSR) when compared to natural conception?

SUMMARY ANSWER

IVF and ICSI as well as the stage of embryo transfer does impact the overall SSR.

WHAT IS KNOWN ALREADY

The World Health Organization quotes SSR for natural conception to range between 103 and 110 males per 100 female births.

STUDY DESIGN SIZE DURATION

A total of 1 376 454 ART cycles were identified, of which 1 002 698 (72.8%) cycles involved IVF or ICSI. Of these, 863 859 (85.2%) were fresh cycles and 124 654 (12.4%) were frozen cycles. Missing data were identified in 14 185 (1.4%) cycles.

PARTICIPANTS/MATERIALS SETTING METHODS

All cycles recorded in the anonymized UK Human Fertilisation and Embryology Authority (HFEA) registry database between 1991 and 2016 were analysed. All singleton live births were included, and multiple births were excluded to avoid duplication.

MAIN RESULTS AND THE ROLE OF CHANCE

The overall live birth rate per cycle for all IVF and ICSI treatments was 26.2% (n = 262 961), and the singleton live birth rate per cycle was 17.1% (n = 171 399). The overall SSR for this study was 104.0 males per 100 female births (binomial exact 95% CI: 103.1-105.0) for all IVF and ICSI cycles performed in the UK recorded through the HFEA. This was comparable to the overall SSR for England and Wales at 105.3 males per 100 female births (95% CI: 105.2-105.4) from 1991 to 2016 obtained from the Office of National Statistics database. Male predominance was seen with conventional insemination in fresh IVF treatment cycles (SSR 110.0 males per 100 female births; 95% CI: 108.6-111.5) when compared to micro-injection in fresh ICSI treatment cycles (SSR 97.8 males per 100 female births; 95% CI: 96.5-99.2; odds ratio (OR) 1.16, 95% CI 1.12-1.19, P < 0.0001), as well as with blastocyst stage embryo transfers (SSR 104.8 males per 100 female births; 95% CI: 103.5-106.2) when compared to a cleavage stage embryo transfer (SSR 101.2 males per 100 female births; 95% CI: 99.3-103.1; OR 1.03, 95% CI 1.01-1.06, P = 0.011) for all fertilization methods.

LIMITATIONS REASONS FOR CAUTION

The quality of the data relies on the reporting system. Furthermore, success rates through ART have improved since 1991, with an increased number of blastocyst stage embryo transfers.

WIDER IMPLICATIONS OF THE FINDINGS

This is the largest study to date evaluating the impact of ART on SSR. The results demonstrate that, overall, ART does have an impact on the SSR when assessed according to the method of fertilization (ICSI increased female births while IVF increased males). However, given the ratio of IVF to ICSI cycles at present with 60% of cycles from IVF and 40% from ICSI, the overall SSR for ART closely reflects the population SSR for, largely, natural conceptions in England and Wales.

STUDY FUNDING/COMPETING INTERESTS

The study received no funding. C.M.B. is a member of the independent data monitoring group for a clinical endometriosis trial by ObsEva. He is on the scientific advisory board for Myovant and medical advisory board for Flo Health. He has received research grants from Bayer AG, MDNA Life Sciences, Volition Rx and Roche Diagnostics as well as from Wellbeing of Women, Medical Research Council UK, the NIH, the UK National Institute for Health Research and the European Union. He is the current Chair of the Endometriosis Guideline Development Group for ESHRE and was a co-opted member of the Endometriosis Guideline Group by the UK National Institute for Health and Care Excellence (NICE). I.G. has received research grants from Wellbeing of Women, the European Union and Finox.

TRIAL REGISTRATION NUMBER

Not applicable.

Write a Scientific Paper (WASP) - What can I publish [1]? Types of studies

As an experienced writer, one is often asked the question "what can I publish" by younger and inexperienced colleagues who must publish. This paper will briefly review the reasons why academics publish and will then outline what kind of papers one may be able to publish with relative ease, using personal experience and citing first hand material as a practical guide. Potential authors must cultivate "a lean and hungry look" as competition from fellow writers is stiff, and editors are choosy. However, do take heart - if we, older colleagues did and can, you can too.

Is sex ratio at birth an appropriate measure of prenatal sex selection? Findings of a theoretical model and its application to India

Son preference and prenatal sex selection against females have resulted in significant sex ratio at birth (SRB) imbalances well documented in several Asian countries, including India and China. The SRB bias is generally used as indicator for the extent and trends of prenatal sex selection against females. Decreasing fertility levels are expected to increase sex selection and thus SRB bias, since desiring fewer children increases the risk for families to remain sonless (fertility squeeze effect). We developed and employ mathematical models linking family size, birth order and childbearing strategies with population SRB bias. We show that SRB bias can increase despite fewer sex selection interventions occurring, inconsistent with the expectation of the fertility squeeze effect. We show that a disproportionality effect of fertility reduction amplifies SRB bias, in addition to the fertility squeeze effect, making SRB bias an inaccurate indicator for changes in sex selection practices within a population. We propose to use sex selection propensity (proportion of couples intervening) to measure behavioural change and evaluate policies targeting sex selection practices. We apply our findings to India, showing for instance that sex selection propensity in Punjab and Delhi was lower than in Rajasthan or Uttar Pradesh, despite significantly higher SRB bias in the former. While we observe a continuous overall increase in the SRB over the 2005–2010 period in India, our results indicate that prenatal sex selection propensity started declining during that period.

Live birth sex ratios and father's geographic origins in Jerusalem, 1964-1976

OBJECTIVE

To examine whether ancestry influenced sex ratios of offspring in a birth cohort before parental antenatal sex selection influenced offspring sex.

METHODS

We measured the sex ratio as the percent of males according to countries of birth of paternal and maternal grandfathers in 91,459 live births from 1964 to 1976 in the Jerusalem Perinatal Study. Confidence limits (CI) were computed based on an expected sex ratio of 1.05, which is 51.4% male.

RESULTS

Of all live births recorded, 51.4% were male. Relative to Jewish ancestry (51.4% males), significantly more males (1,761) were born to Muslim ancestry (54.5, 95% CI = 52.1-56.8, P = 0.01). Among the former, sex ratios were not significantly associated with paternal or maternal age, education, or offspring's birth order. Consistent with a preference for male offspring, the sex ratio decreased despite increasing numbers of births over the 13-year period. Sex ratios were not affected by maternal or paternal origins in North Africa or Europe. However, the offspring whose paternal grandfathers were born in Western Asia included fewer males than expected (50.7, 50.1-51.3, P = 0.02), whether the father was born abroad (50.7) or in Israel (50.8). This was observed for descendents of paternal grandfathers born in Lebanon (47.6), Turkey (49.9), Yemen & Aden (50.2), Iraq (50.5), Afghanistan (50.5), Syria (50.6), and Cyprus (50.7); but not for those from India (51.5) or Iran (51.9). The West Asian group showed the strongest decline in sex ratios with increasing paternal family size.

CONCLUSIONS

A decreased sex ratio associated with ancestry in Western Asia is consistent with reduced ability to bear sons by a subset of Jewish men in the Jerusalem cohort. Lower sex ratios may be because of pregnancy stress, which may be higher in this subgroup. Alternatively, a degrading Y chromosome haplogroup or other genetic or epigenetic differences on male germ lines could affect birth ratios, such as differential exposure to an environmental agent, dietary differences, or stress. Differential stopping behaviors that favor additional pregnancies following the birth of a daughter might exacerbate these lower sex ratios.

Blastocyst transfer and gender: IVF versus ICSI

PURPOSE

To investigate the difference in sex ratio in our centre after day 5 embryo transfer among neonates delivered after fresh in vitro fertilization (IVF), fresh intra cytoplasmatic sperminjection (ICSI) and frozen embryo replacement (FER) compared to expected sex ratio in normal population.

METHODS

Retrospective data after IVF/ICSI/FER therapy from 1995 - 2007 and data from the literature on similar subjects.

RESULTS

Among a total of 420 births after day 5 transfer, there were 225 male and 195 female babies. However, after ICSI alone 30 were female and 21 male. Adding all available data from the literature on gender ratio after long term culture, the ratio of male births to total births (0.545) was significantly (p = 0.004) different from the expected ratio (0.515).

CONCLUSIONS

It appears that significantly more males are born than expected after day 5 transfer in IVF. However, a subgroup analysis in our data comparing IVF, ICSI and FER revealed more females born after ICSI and FER, suggesting that further research is needed in this area.

Population-based estimates of still birth, induced abortion and miscarriage in the Indian state of Bihar

Background

We report population-based data on still birth, induced abortion and miscarriage from the Indian state of Bihar to assess the magnitude of the problem and to inform corrective action.

Methods

A representative sample of women from all districts of Bihar with a pregnancy outcome in the last 12 months was obtained through multistage sampling in early 2012. Still birth rate was calculated as fetuses born with no sign of life at 7 or more months of gestation per 1,000 births. Induced abortion and miscarriage rates were defined as expulsion of dead fetuses at less than 7 months of gestation induced by any means or without inducement, respectively, per 1000 pregnancies that had an outcome. Multiple regression models were used to explore possible associations with stillbirths, induced abortions and miscarriages. Multi-level models were developed for the relatively less developed north zone and for the south zone of Bihar to examine contextual factors associated with still births, induced abortions and miscarriages.

Results

Still birth rate was estimated as 20 per 1,000 births (95% CI 15.6-24.5), and induced abortion and miscarriage rates as 8.6 (6.6-10.6), and 46 (40.8-51.3) per 1,000 pregnancies with outcome, respectively. The odds of induced abortion and miscarriage were significantly higher in the south zone (odds ratio 2.53 [95% CI 1.79-3.57] and 1.27 [95% CI 1.10-1.47], respectively). In the multi-level model for the north zone, the odds of induced abortion were higher for women with husband’s having mean years of education higher than the state mean (2.62; 95% CI 1.47-4.69). Among the nine divisions of Bihar, comprising of groups of districts, higher induced abortion rate was associated with lower neonatal mortality rate (R² = 0.68, p = 0.01).

Conclusions

These population-based data show a significant burden of still births in Bihar, suggesting that addressing these must become an important part of maternal and child health initiatives. The higher induced abortion in the more developed districts, and the inverse trend between induced abortion and neonatal mortality rates, have programmatic implications.

Electronic supplementary material

The online version of this article (doi:10.1186/s12884-014-0413-z) contains supplementary material, which is available to authorized users.

Secular trends in newborn sex ratios

A wide variety of factors have been shown to influence the male to female ratio at birth, which invariably displays a male excess. This paper will review and amplify recent work by the author, with specific references to individual countries, regions and entire continents in order to provide a global overview of this subject. It will be shown that stress, including stress related to political events, influences this ratio. Man-made radiation is also shown to have played a significant role in relation to the Windscale fire (1957) and Chernobyl (1986).

Administration of estradiol benzoate before insemination could skew secondary sex ratio toward males in Holstein dairy cows

The present study was conducted to investigate the effect of estradiol benzoate administration before insemination on secondary sex ratio (proportion of male calves at birth) in Holstein dairy cows. Cows (n = 1,647) were randomly assigned to 2 experimental groups by parity over a 1-yr period. Cows in the control group (n = 827; 232 primiparous and 595 multiparous cows) received 2 administrations of PGF2α (500 μg) 14 d apart, started at 30 to 35 d postpartum. Twelve d after the second PGF2α injection, cows received GnRH (100 μg), followed by administration of PGF2α 7 d later. Cows in the treatment group (n = 820; 238 primiparous and 582 multiparous cows) received the same hormonal administrations as the cows in the control group. Additionally, cows in the treatment group received estradiol benzoate (1 mg) 1 d after the third PGF2α injection. Estrus detection by visual observation was started 1 d after the third PGF2α injection and after estradiol administration in the control (for 6 d) and treatment (for 36 h) groups, respectively. Artificial insemination was carried out 12 h after observation of standing estrus. Exposure of cows to heat stress at conception was determined based on temperature-humidity index. Estrus detection rate was lower in primiparous than in multiparous cows (P < 0.05), but conception rate was higher in primiparous vs multiparous cows (P < 0.05). Estradiol administration improved estrus detection rate and fertility (P < 0.05); moreover, it increased secondary sex ratio (adjusted odds ratio: 1.645; P = 0.017). Exposure to heat stress diminished heat detection rate and fertility (P < 0.05), and altered secondary sex ratio toward males (adjusted odds ratio: 2.863; P = 0.012). In conclusion, the present study revealed that estradiol administration before insemination could improve fertility and increase the probability of calves being male in Holstein dairy cows. Moreover, the results showed that cows exposed to heat stress around conception had diminished fertility and increased secondary sex ratio.

Secular trends and latitude gradients in the male-female ratio at birth in Yugoslavia and the ex-Yugoslavian States

BACKGROUND

Latitude gradients and secular trends in Europe and North America have been found in the male-female ratio at birth (M/F: male births divided by total births) which approximates 0.515.

METHODS

Annual national data for Yugoslavia and the post-Yugoslavia States for male and female live births were obtained from the World Health Organisation and analysed with contingency tables.

RESULTS

This study analysed 22,020,729 live births. There was a increasing trend in M/F prior to the breakup of the former Yugoslavia (1950-1990, p = 0.002), followed by a decreasing trend after 1990 (p = 0.02). A latitude gradient was also noted, with more males being born in southern, warmer latitudes (p < 0.0001). There was an overall excess of 42,753 male births based on an anticipated M/F of 0.515.

CONCLUSION

M/F is decreasing in this region, similar to the rest of Europe and North America. A latitude gradient is also present with more males being born in warmer (more Southern) latitudes (p < 0.0001), even in this small region and over the short time-frame studied.

Secular trends in sex ratios at birth in South America over the second half of the 20(th) century

OBJECTIVES

Latitude gradients have been found in the male-female ratio at birth (M/F: male divided by total births), which is anticipated to be 0.515.

METHODS

Annual national male and female live births by country were obtained for South America from the World Health Organization (WHO) and analysed with contingency tables. The continent was arbitrarily divided into two regions: a region 10° above the Equator to 20° below the Equator, and a second area 20° below the Equator.

RESULTS

This study analyzed 147,773,689 live births. An overall increasing trend in M/F was found for the region >20° (p<0.0001) for the entire period. For the aggregate, a significant decrease was present for the period 1950-74 (p = 0.01) followed by a significant increase thereafter (p<0.001). A latitude gradient was also noted, with more males being born in cooler (more Southern > 20° S) latitudes (p<0.0001). There were 3,765,648 male births in excess of what was anticipated.

CONCLUSION

The M/F ratio is increasing in South America, unlike the decline present in Europe and North America. This study also showed that M/F latitude gradients are similar to those previously reported in North America, with more males being born in cooler latitudes, contrary to the trends reported in Europe. The interplay of several poorly understood factors is likely.

Sex ratios at birth in the British Isles over the past sixty years

The male-female ratio at birth (M/F: male births divided by total births) is anticipated to approximate 0.515. This has been shown to be declining in industrialised countries and to be displaying a latitude gradient in Europe, with more males born in warmer, southern climates. Annual national data for the British Isles for male and female live births were obtained from the World Health Organization and analysed with contingency tables. Analysis was performed separately for individual countries and for totals for the northern (Scotland and Northern Ireland) and southern (England and Wales, and the Republic of Ireland) regions. This study analysed 49,263,493 live births. There was an overall rise in M/F up to the late 1970s, followed by a decline thereafter. The step-down for the periods of 1975-1979 to 1980-1984 was highly significant for both the northern (p = 0.001) and southern regions (p < 0.0001). An overall decreasing trend in M/F was noted (p = 0.04) which reversed the expected European latitude gradient. More males are born in Scotland and Northern Ireland than in England and Wales, and the Republic of Ireland (p = 0.02). There was a male deficit of 59,311 live births.

CONCLUSION

M/F is decreasing in the British Isles, to the south more than to the north, to the extent that the expected latitude gradient is reversed. The interplay of several poorly understood factors is likely.

Secular trends and latitude gradients in sex ratio at birth in Asia during the past 60 years

BACKGROUND

Latitude gradients and secular trends in Europe and North America have been found in the male-female ratio at birth (M/F: male births divided by total births), which is anticipated to approximate 0.515.

METHODS

Annual national data for Asian countries for male and female live births were obtained from the World Health Organization and analyzed with contingency tables.

RESULTS

A total of 245,938,211 live births were analyzed. An overall increasing trend in M/F was found (P < 0.0001). A latitude gradient was also noted, with more boys being born in southern, warmer latitudes (P < 0.0001). There was an overall deficit of 1,351,757 male births based on an anticipated M/F of approximately 0.515.

CONCLUSION

M/F is increasing overall in Asia, unlike the decline previously noted in Europe and North America. Moreover, it had been shown that there is a higher incidence of male births in southern Europe than in the north, with the opposite gradient in North America. This paper shows that M/F latitude gradients in Asia are in keeping with those of Europe. The overall M/F in Asia may be rising due to improving socioeconomic conditions, and the interplay of several poorly understood factors is likely.

Secular trends and latitude gradients in sex ratios at birth in Czechoslovakia and the post-Czechoslovakian states

Latitude gradients and secular trends in Europe and North America have been found in the male-female ratio at birth (M/F: male births divided by total births) which is expected to be 0.515. Annual national data for Czechoslovakia and the post-Czechoslovakian (Czech Republic and Slovakia) countries for male and female live births were obtained from the World Health Organisation and analysed with contingency tables. This study analysed 13,123,538 live births. An overall decreasing trend in M/F was found (p < 00001). No latitude gradient was noted. There was an overall deficit of 15,232 male births based on an M/F of 0.515. M/F is declining in this region, despite well developing economies that have resisted the worldwide slowdown. An interplay of several poorly understood factors is likely.

Secular trends and latitude gradients in sex ratios at birth in the former Soviet Republics

BACKGROUND

The male-female ratio at birth (M/F: male births divided by total births), which is anticipated to approximate 0.515, has been shown to exhibit latitude gradients and secular trends.

METHODS

Annual national data for male and female live births for the 15 countries that comprise the former Soviet Union were obtained from the World Health Organisation for the period 1980-2009 (115,167,569 total live births) and analysed with contingency tables. Spearman correlation was also carried out to compare percentage annual gross domestic product growth (GDP%--downloaded from the World Bank) and M/F. In this context, GDP% is used as a measure for economic hardship or wellbeing within the populace.

RESULTS

There have been overall highly significant secular increases in M/F (p < 0.0001) in the countries and regions investigated. M/F is significantly lower in the three more northern regions (Russian Federation, Baltic States and Central Asia. M/F 0.51324, 0.51335-0.51314) than the two more southern regions (Southern Caucasus and Eastern Europe. M/F 0.51654, 0.51635-0.51672). There was a male excess of 113,818 live births.There was a significant positive correlation between GDP% and M/F for Armenia, Azerbaijan and Uzbekistan. There was a significant negative correlation in Estonia.

CONCLUSION

Previous studies have shown that improving socioeconomic conditions increase M/F, and the converse has also been demonstrated. This is a potential influence in this geographical area since this region has relatively recently emerged from communist rule and experienced an overall economic upturn, but is only partially supported using GDP%. Another factor may be the selective termination of female pregnancies. The latitude gradient parallels that of neighbouring Europe but no theory has been put forward to convincingly explain this finding to date.

Sex ratios at birth in Scandinavia over the past sixty years

BACKGROUND

The gender ratio at birth (M/F: male births divided by total births) is expected to approximate 0.515. This has shown to be declining in industrialised countries and to display a latitude gradient in Europe, with more males born in southern climates.

METHODS

Annual national data for Scandinavian countries for male and female live births were obtained from the World Health Organisation and analysed with contingency tables.

RESULTS

This study analysed 18,250,193 live births. A significant decreasing trend in M/F was noted in all countries except Norway, and overall. There was no latitude gradient. M/F was less than 0.515 for almost all countries, with a resultant male deficit of 19,517 live births.

CONCLUSIONS

M/F is decreasing in Scandinavia and M/F overall is <0.515. The interaction of several poorly comprehended factors is likely.

Parasite stress predicts offspring sex ratio

In this study, I predict that the global variation of offspring sex ratio might be influenced in part by the level of parasite stress. From an energetic standpoint, higher gestational costs of producing a male offspring could decrease male births in a population with limited resources. This implies that, any factor that limits the parental resources could be expected to favor female offspring production. Human sex ratio at birth (SRB) is believed to be influenced by numerous socioeconomic, biological, and environmental factors. Here, I test a prediction that parasite stress, by virtue of its effects on the general health condition, may limit the parental investment ability and therefore could influence the SRB at the population level. The statistical analysis supports this prediction, and show that the level of parasite stress has a significant inverse relation with population SRB across the world. Further, this relation is many-folds stronger than the association of SRB with other factors, like; polygyny, fertility, latitude, and son-preference. Hence, I propose that condition affecting ability of parasites (but not adaptive significance) could be a likely causal basis for the striking variation of SRB across populations.

Whatever the weather: ambient temperature does not influence the proportion of males born in New Zealand

Background

The proportion of male births has been shown to be over 50% in temperate climates around the world. Given that fluctuations in ambient temperature have previously been shown to affect sex allocation in humans, we examined the hypothesis that ambient temperature predicts fluctuations in the proportion of male births in New Zealand.

Methodology/Principal Findings

We tested three main hypotheses using time series analyses. Firstly, we used historical annual data in New Zealand spanning 1876–2009 to test for a positive effect of ambient temperature on the proportion of male births. The proportion of males born ranged by 3.17%, from 0.504 to 0.520, but no significant relationship was observed between male birth rates and mean annual temperature in the concurrent or previous years. Secondly, we examined whether changes in annual ambient temperature were negatively related to the proportion of male stillbirths from 1929–2009 and whether the proportion of male stillbirths negatively affected the proportion of male live births. We found no evidence that fewer male stillbirths occurred during warmer concurrent or previous years, though a declining trend in the proportion of male stillbirths was observed throughout the data. Thirdly, we tested whether seasonal ambient temperatures, or deviations from those seasonal patterns, were positively related to the proportion of male births using monthly data from 1980–2009. Patterns of male and female births are seasonal, but very similar throughout the year, resulting in a non-seasonal proportion of male births. However, no cross correlations between proportion of male births and lags of temperature were significant.

Conclusions

Results showed, across all hypotheses under examination, that ambient temperatures were not related to the proportion of male births or the proportion of male stillbirths in New Zealand. While there is evidence that temperature may influence human sex allocation elsewhere, such effects of temperature are not universal.

Evolutionary ecology of human birth sex ratio under the compound influence of climate change, famine, economic crises and wars

1. Human sex ratio at birth at the population level has been suggested to vary according to exogenous stressors such as wars, ambient temperature, ecological disasters and economic crises, but their relative effects on birth sex ratio have not been investigated. It also remains unclear whether such associations represent environmental forcing or adaptive parental response, as parents may produce the sex that has better survival prospects and fitness in a given environmental challenge. 2. We examined the simultaneous role of wars, famine, ambient temperature, economic development and total mortality rate on the annual variation of offspring birth sex ratio and whether this variation, in turn, was related to sex-specific infant mortality rate in Finland during 1865-2003. 3. Our findings show an increased excess of male births during the World War II and during warm years. Instead, economic development, famine, short-lasting Finnish civil war and total mortality rate were not related to birth sex ratio. Moreover, we found no association between annual birth sex ratio and sex-biased infant mortality rate among the concurrent cohort. 4. Our results propose that some exogenous challenges like ambient temperature and war can skew human birth sex ratio and that these deviations likely represent environmental forcing rather than adaptive parental response to such challenges.

Humans at tropical latitudes produce more females

Skews in the human sex ratio at birth have captivated scientists for over a century. The accepted average human natal sex ratio is slightly male biased, at 106 males per 100 females or 51.5 per cent males. Studies conducted on a localized scale show that sex ratios deviate from this average in response to a staggering number of social, economical and physiological variables. However, these patterns often prove inconsistent when expanded to other human populations, perhaps because the nature of the influences themselves exhibit substantial cultural variation. Here, data collected from 202 countries over a decade show that latitude is a primary factor influencing the ratio of males and females produced at birth; countries at tropical latitudes produced significantly fewer boys (51.1% males) annually than those at temperate and subarctic latitudes (51.3%). This pattern remained strong despite enormous continental variation in lifestyle and socio-economic status, suggesting that latitudinal variables may act as overarching cues on which sex ratio variation in humans is based.

A simple model for adaptive variation in the sex ratios of mammalian offspring

We present a simple mathematical model that describes how primary and secondary sex ratios of offspring may vary adaptively in order to maintain equal numbers of the sexes at the age of reproductive maturity. The model postulates that the sex of an offspring depends probabilistically on a weighted linear combination of maternal testosterone and male vulnerability. The model operates at population level, and is based on three physiological phenomena: first that maternal testosterone in follicular fluid is normally distributed, with levels above the mean more likely to be associated with the conception of males; secondly, that males are more vulnerable than females from conception onwards; and thirdly that under conditions of chronic stress, increased secretion of female testosterone coincides with increased male vulnerability. Thus during times of chronic stress, more males are conceived, but their number of live births is moderated by increased male loss. Variations in secondary sex ratios should therefore be related not only to the stressfulness of environmental conditions, but also to the timing of changes in stressfulness.

Temperature-related birth sex ratio bias in historical Sami: warm years bring more sons

The birth sex ratio of vertebrates with chromosomal sex determination has been shown to respond to environmental variability, such as temperature. However, in humans the few previous studies on environmental temperature and birth sex ratios have produced mixed results. We examined whether reconstructed annual mean temperatures were associated with annual offspring sex ratio at birth in the eighteenth to nineteenth century Sami from northern Finland. We found that warm years correlated with a male-biased sex ratio, whereas a warm previous year skewed sex ratio towards females. The net effect of one degree Celsius increase in mean temperature during these 2 years corresponded to approximately 1% more sons born annually. Although the physiological and ecological mechanisms mediating these effects and their evolutionary consequences on parental fitness remain unknown, our results show that environmental temperature may affect human birth sex ratio.

Association of secondary sex ratio with smoking and parity

OBJECTIVE

To assess the sex ratio in offspring of smoking and nonsmoking mothers in relationship to parity.

DESIGN

Prospective study.

SETTING

University hospital.

PATIENT(S)

The authors studied 2,108 term singleton neonates born between 1993 and 2002, 665 from smoking mothers and 1,443 from nonsmoking mothers.

INTERVENTION(S)

A prospective recording of maternal age, parity and smoking status, and gender of neonates delivered over a 10-year period.

MAIN OUTCOME MEASURE(S)

Secondary sex ratio in regard to maternal smoking and parity.

RESULT(S)

The offspring sex ratio in the total sample studied was 1.09; in the offspring of smoking and nonsmoking mothers, it was 1.26 and 1.03, respectively, a statistically significant difference. In the offspring of smoking women who had parity 1, 2, and >or=3, it was 1.47, 1.35, and 0.92, whereas in those of nonsmoking women, it was 1.04, 1.00, and 1.03, respectively (the differences of the parity 1 and 2 groups between the offspring of smoking and nonsmoking mothers were statistically significant). Logistic regression analysis showed that the possibility of a boy being delivered by a mother who smoked was significantly greater in primiparous women than in women who had parity >or=3, independent of the maternal age. Conversely, parity did not affect significantly the sex ratio in the offspring of nonsmoking women.

CONCLUSION(S)

The findings suggest that among women who smoked, significantly more male than female offspring are born from primiparous women, whereas women who had parity >or=3 gave birth to more female offspring; biparous women give birth to significantly more male offspring, but the offspring sex ratio declined with the number of cigarettes when the mothers smoked >or=10 cigarettes per day.

Secondary sex ratio variation during stressful times: the impact of the French revolutionary wars on a German parish (1787-1802)

The observation that declines in the human secondary sex ratio (SSR) may be linked to stressful periconceptional periods has received considerable attention (Catalano [2003] Hum Reprod 18:1972-1975; Catalano et al. [2005] Int J Epidemiol 34:944-948, [2005] Hum Reprod 20:1221-1227, [2005] Paediatr Perinat Epidemiol 19:413-420). For the purpose of testing the external validity of this phenomenon, birth records from four German village genealogies (N = 1,048) were analyzed to study the impact of the French Revolutionary Wars (1787-1802) on the proportion of male births. All births were subdivided into three cohorts (prewar, 1787-1792; war, 1792-1797; and postwar, 1797-1802). Differences in SSR between cohorts achieved statistical significance (chi2= 7.695; df = 2; P = 0.021). In addition, changes in SSR before, during, and after the wars were monitored by risk analysis. Using the SSR of the prewar period as a control, the results of the war cohort failed to achieve statistical significance (regression coefficient, -0.257; ExpB= 0.773; P = 0.118), while the odds reduction of 32.3% in the postwar period proved to be statistically significant (regression coefficient, -0.390; ExpB= 0.677; P = 0.006). It is hypothesized that the experience of postwar economic hardship (attributable to lowered food availability paired with dietary changes) represents the most likely proximate cause. The study also finds evidence of a parental sex ratio manipulation strategy meant to offset the female-biased SSR after the wars. It is argued that from an evolutionary perspective both the decline in SSR in response to stress as well as parental manipulation of the tertiary sex ratio convey reproductive advantages.

Trends in the sex ratio of California births, 1960-1996

STUDY OBJECTIVE

The male sex ratio at birth (or the proportion of male births in a population) has been suggested as a sentinel environmental health indicator. Usually around 51%, the proportion may be dramatically decreased in offspring of persons with chemical exposures. Recent publications from the USA and elsewhere have noted a small but apparently declining male birth proportion, suggesting the effect of some environmental exposures. This paper sought to examine these trends more closely in California's large and diverse population.

DESIGN

Using computerised birth certificate data, time trends were examined by multivariate linear and spline regression, controlling for demographic factors.

SETTING

California.

PARTICIPANTS

About 15 million births from 1960 to 1996.

MAIN RESULTS

In the raw data, the male birth proportion is indeed declining. However, during this period, there were also shifts in demographics that influence the sex ratio. Controlling for birth order, parents' age, and race/ethnicity, different trends emerged. White births (which account for over 80%) continued to show a statistically significant decline, while other racial groups showed non-statistically significant declines (Japanese, Native American, other), little or no change (black), or an increase (Chinese). Finally, when the white births were divided into Hispanic and non-Hispanic (possible since 1982), it was found that both white subgroups suggest an increase in male births.

CONCLUSION

This analysis shows that the decline in male births in California is largely attributable to changes in demographics.

Solar cycles and their relationship to human disease and adaptability

In this paper, we show that 11-year solar cycle peaks predispose humans to disease, but also endow creativity and adaptability. We give several examples of diseases that are modulated by light and present evidence for an effect of intensity and variation in sunlight, primarily ultraviolet radiation (UVR), on the human genome. The birth dates of nearly 237,000 unique clients in the Maine Medicaid database collected from 1995 to 2004, inclusive, were related to solar cycle irradiance for the past seventy-one years, encompassing seven solar cycles. The sample was divided into four general categories of disease: mental/behavioral illnesses; metabolic diseases; autoimmune diseases; neoplasms. The birth months for those clients born in any given year were arranged in the form of a winter/summer ratio in order to more clearly appreciate the seasonality inherent in each disease category. Solar cycles were separated into chaotic (approximately three times as irradiant) or non-chaotic according to the Gutenberg-Richter power law and the uncertainty inherent in predicting solar storms. The results show that radiation peaks in solar cycles and particularly in chaotic solar cycles (CSCs) are associated with a higher incidence of mental disorders, suggesting the sensitivity of ectodermal embryonic tissues to UVR. Autoimmune diseases have intermediate sensitivity, while the neoplasms in the study, primarily of endoderm, appear suppressed by peak UVR intensity. The ratio of the number of clients born in CSC cycles to non-CSC cycles was highest for the more genetic mental diseases, like schizophrenia and bipolar disorder, but as that ratio decreased, the clients with diseases like multiple sclerosis and rheumatoid arthritis showed more environmental features manifested as a greater winter/summer birth month ratio that was significantly different than that of the average client in the whole data set. The paper presents evidence that latitude, e.g., variation in light, is an added stress to the immune system (especially at 53-54 degrees N. latitude) that is involved in nearly all human disease. We hypothesize that introns, the presumptive engenderers of gene control, modulate the effects of UVR, particularly for the neoplasms studied. We conclude that intermittent and largely unpredictable peak solar cycle radiation has been the fundamental engine of evolution, forcing organisms to adapt to mutagenic UVR and producing enough damage to instigate genetic variation. Probably a chance genetic mutation over 80,000 years ago produced a human brain capable of abstract thought and consciousness. The slight genetic instability that favored an adaptable, creative brain also produced other somatic variations that present phenotypically as disease, but largely expressed after natural selection (reproduction) and associated with the inexorable entropy of aging.

Mass screening for coeliac disease using antihuman transglutaminase antibody assay

AIMS

To determine coeliac disease prevalence by an anti-transglutaminase antibody assay in a large paediatric population; to evaluate acceptance of the screening programme, dietary compliance, and long term health effects.

METHODS

Cross-sectional survey of 3188 schoolchildren (aged 6-12) and prospective follow up of diagnosed cases. Main outcome measures were: prevalence of coeliac disease defined by intestinal biopsy or positivity to both human tissue transglutaminase and anti-endomysium antibodies in HLA DQ2-8 positive subjects; percentage of children whose families accepted screening; dietary compliance as defined by negativity for anti-transglutaminase antibodies; and presence of clinical or laboratory abnormalities at 24 month follow up.

RESULTS

The families of 3188/3665 children gave their consent (87%). Thirty biopsy proven coeliacs were identified (prevalence 1:106). Three other children testing positive for both coeliac related autoantibodies and HLA DQ2-8 but refusing biopsy were considered as having coeliac disease (prevalence 1:96). Of 33 cases, 12 had coeliac related symptoms. The 30 biopsy proven coeliacs followed a gluten-free diet. Of 28 subjects completing 18-24 months follow up, 20 (71.4%) were negative for anti-transglutaminase antibodies, while eight were slightly positive; symptoms resolved in all 12 symptomatic children.

CONCLUSIONS

Prevalence of coeliac disease is high in Italian schoolchildren. Two thirds of cases were asymptomatic. Acceptance of the programme was good, as was dietary compliance. Given the high prevalence and possible complications of untreated coeliac disease, the availability of a valid screening method, and evidence of willingness to comply with dietary treatment population mass screening deserves careful consideration.

Social trends in singleton births and birth weight in Wirral residents, 1990-2001

OBJECTIVE

To examine social trends in the number of singleton births and birth weight in an English health district between 1990 and 2001, using an area based deprivation index.

DESIGN

Analysis of routinely collected hospital data.

SETTING

Wirral Health District in north west England.

PARTICIPANTS

All 48 452 live births to Wirral residents from 1990 to 2001.

MAIN OUTCOME MEASURES

Birth numbers, birth weight, and standard deviation score for birth weights for singleton births. Townsend material deprivation scores derived from postcodes.

RESULTS

The number of singleton births fell by 28% over the 12 years. The fall in the least deprived Townsend quartile (45%) was more than triple that in the most deprived quartile (gamma = 0.045; 95% confidence interval (CI) = 0.036 to 0.054; p < 0.001). Over the study period, the mean birth weight in the least deprived Townsend quartile was 141 g higher than in the most deprived quartile. There was a highly significant association between the standard deviation score for birth weight and Townsend quartile (tau-b = -0.062; 95% CI = -0.068 to -0.055; p < 0.001). Numbers of low birth weight babies in the least deprived quartile fell disproportionately compared with those from the most deprived quartile (gamma = 0.17; 95% CI = 0.09 to 0.25; p < 0.001).

CONCLUSION

The reduction in birth rate in the Wirral was significantly less in the most deprived districts. This was accompanied by related differences in mean birth weight and the number of low birth weight babies, indicating increasing social inequality in birth trends. Previously described social inequity in birth weight and the number of low birth weight babies continues in the north west of England.

Secular trends in sex ratios at birth in North America and Europe over the second half of the 20th century

CONTEXT

A previous study showed that significantly more boys were born in southern latitudes in Europe than in northern latitudes and the converse pattern was observed in North America.

OBJECTIVE

This study analyses secular trends in gender ratios for live births over the second half of the 20th century.

DESIGN, SETTING, PARTICIPANTS

Analysis was carried out from a World Health Organisation dataset comprising live births over the above period. This included 127034732 North American and 157947117 European live births.

MAIN OUTCOME MEASURES

Analysis of trends in gender ratios for countries in both continents.

RESULTS

The findings show a highly significant overall decline in male births in both Europe and North America (p<0.0001), particularly in Mexico (p<0.0001). Interestingly, in Europe, male births declined in North European countries (latitude>40 degrees, p<0.0001) while rising in Mediterranean countries (latitude congruent with 35-40 degrees, p<0.0001). These trends produced an overall European male live birth deficit 238693 and a North American deficit of 954714 (total male live birth deficit 1193407).

CONCLUSIONS

No reasonable explanation/s for the observed trends have been identified and the causes for these trends may well be multifactorial.