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Introduction: Many factors have been shown to influence the male to female ratio at birth (M/T). Celebrations increase M/T nine months later, putatively due to elevated coital rates. The Super Bowl (SBS) is consistently held in the first Sunday in February. This study was carried out in order to ascertain whether SBS results in a rise in M/T nine months later, and whether any such changes are influenced by race and census region.Methods: Births were studied for the period 2003-2015. Seasonality adjustment was applied in order to identify true outlier values over and above those due to natural seasonal M/T variation.Results: This study analysed 53,105,069 births. M/T was elevated in all regions, for all races for 11/2006, 9/2009, 10/2009, 10/2010, 12/2010, 11/2011, 11/2013 and 12/2013. A similar effect is observed in the West Region for all births. For the various ethnic groups, the effect is strongest for Whites in regions Northeast, South and West, and for Black/African American births in regions Midwest and South.Discussion: Events which increase coital activity elevate M/T nine months later as M/T follows a U-shaped regression on cycle day of insemination, with male conceptions occurring more frequently at the beginning (and end) of the menstrual cycle. SBS is a significant annual celebratory event in contemporary American culture. It is possible that increased coital rates during this period (perhaps due to a combination of celebration and inebriation) may result in the M/T rises nine months later observed in this study. [ABSTRACT FROM AUTHOR]

Background: Males are born in excess of females, a ratio expressed as M/T (males:total births). The ratio exhibits seasonal variation. Furthermore, acute stressful events may result in a transient dip in male births due to excess foetal losses, reducing M/T.Aims: This study was carried out in order to identify significant M/T dips after adjusting for seasonality.Study Design: Live births by gender and month were sought for acute stressful events. After seasonal correction (where appropriate), M/T dips were sought.Subjects: Live births.Outcome Measures: M/T dips.Results and Conclusions: This paper studied 112,226,306 live births. The following events showed dips ≤5th percentile 3-5months after these acute episodes: the Brooklyn Bridge protests, Katrina Hurricane for all 4 states and for each individual state (Alabama, Florida, Louisiana, Mississippi), the Battle in Seattle, the London bombings, The Madrid bombings (for Madrid and for Spain), the Breivik shooting, the Oklahoma City bombing and the Sandy Hook Elementary School shooting. The Virginia Polytechnic Institute and State University shooting the Fukushima Daiichi nuclear disaster also showed dips albeit slightly later. Seasonal adjustments should be taken into consideration in order to avoid Type 1 or 2 error pitfalls. [ABSTRACT FROM AUTHOR]

Introduction: Males are usually in excess of females at birth and the ratio is often expressed as M/F (male divided by total births). Several factors have been shown to be associated with changes in M/F, including major terrorist attacks. These are associated with a transient lowering of M/F for a one month period, three to five months after such events. This study was carried out in order to ascertain whether the Madrid March 2004 bombings and the London July 2005 bombings were similarly associated with changes in M/F in their respective populations. Methods: Monthly live births by gender for Madrid and Spain for 2004 and for England and Wales for 2005 were obtained from the two countries' National Statistics Offices. Results: There were no significant dips in M/F for any of the months following the March 2004 bombings in Madrid or in Spain. There were no significant dips in M/F for any of the months following the July 2005 London bombings. Discussion: Research to date has shown M/F dips following catastrophic or tragic events, including major terrorist actions with extensive media coverage. Equivalent dips were not noted in this study for the terrorist acts in these instances. The reasons for this may be one or a combination of the following. The population size was not sufficiently large in order to detect an M/F dip. Alternatively, the events were not felt to be sufficiently momentous by the populace such that an M/F dip was not produced. Yet another possibility is that these particular populations are somehow hardier and more resistant to such influences. Not all terrorist events universally cause a significant reduction in M/F. [ABSTRACT FROM AUTHOR]

Introduction: Male exceed female live births. The ratio is expressed as M/F (male/total live births). Many factors influence this ratio including stress, which depresses it. The 9/11 attacks lowered M/F in the United States a few months after the event. This study was carried out to identify any racial differences in the observed M/F reduction. This paper also analysed racial M/F responses to the assassination of President John Kennedy.Methods: For the JKF assassination, births were available as White and Non-White births. For 9/11, births were available for four racial groups: American Indian/Alaska Native, Asian/Pacific, Black/African and White.Results: For the JFK assassination (November 1963), total M/F was lowest in 1964 (1958-1970, p≤0.01). M/F dipped in March 1964 in Non-White births only (p<0.0001). For 9/11, M/F dips showed a nonsignificant gradient, being greater in Asian/Pacific births, followed by White and Black/African. Baseline M/F was Asian/Pacific>White>Black/African and American Indian/Alaska Native.Discussion: President Kennedy actively attempted to usher in civil rights, and his assassination may have stressed Non-Whites far more than Whites. For 9/11, the low Black/African M/F dips may be due to chronic stress associated with being overall disadvantaged and of lower socio-economic status. These factors decrease M/F and potentially dampen M/F dips in response to additional stressors. The observed M/F dips often exceed the perinatal mortality statistic. Public Health should be more cognizant of the effect of stress on population M/F as a sentinel health indicator.Key Guidelines: 1. The male to female ratio at birth is decreased by stressful events. 2. This is due to an excess of male foetal losses in established pregnancies. 3. Such losses in response to acute events are transient. 4. This ratio may be a useful indicator of population stress. 5. Socioeconomically deprived subpopulations, such as Black/African and American Indian/Alaska Native races may have a low ratio due to chronic stress and may thus be less responsive to stress in their ratio responses.6. The habitually high ratio in Asian/Pacific subpopulations may be due to the former practicing gender-selective abortion, favouring male over female offspring. RESEARCH DIRECTIONS: 1. Gender ratios in populations could be routinely monitored in order to assess the impact of stressful events that may reduce the male to female birth ratio. [ABSTRACT FROM AUTHOR]

Introduction: The male-to-female ratio of live births is expressed as the ratio of male births divided by total births (M/F). Males are produced approximately 3% in excess. A large number of factors have been found to influence M/F. Stress and privation reduces M/F. Gender preference (which almost invariably favours males) with selective female foetal abortion increases M/F. This study was carried out in order to assess a United Nations data set for evidence of global trends in M/F in relation to broad socioeconomic conditions and male preference.Methods: Data (M/F and total births, 1955-2009) was obtained from the United Nations (UN) Department of Economic and Social Affairs, Population Division, Population Estimates and Projection Section. The following regions were analysed: more developed countries, less developed countries and least developed countries (as defined by the UN General Assembly).Results: More developed countries: M/F was initially stable at 0.53 up to 1979 then fell to 0.525. Less developed countries: M/F was initially stable at 0.53 then rose after 1984 to 0.545 with a rise in male births and a fall in female births (estimated female birth deficit=48734993). Least developed countries: exhibited a stable M/F of 0.52 (all p<<0.001).Discussion: This study has confirmed, on a global scale, that least developed countries have the lowest M/F. The rise in M/F in developed countries (which includes Asia) confirms widespread selective female foeticide due to cultural male preference. The declining trend in M/F in developed countries has been previously noted and remains unexplained. [ABSTRACT FROM AUTHOR]

Introduction: Males are usually born in excess of females. The ratio is often expressed as M/F (male divided by total births). A wide variety of factors have been shown to influence M/F. Terrorist attacks reduce M/F. This study was carried out in order to ascertain whether individual terrorist attacks influenced M/F in relevant populations.Methods: The following events were studied: the Troubles in Northern Ireland, the Los Angeles Riots (the Rodney King affair), the Breivik shooting (Norway), and the Sandy Hook shooting (Connecticut).Results: Northern Ireland M/F was significantly lower during the Troubles (1969-1998) than during the period before (p=0.0006). There was a very sharp dip in 1978 (p≤0.004) during this particular year of renewed violence and heavy civilian attacks. Rodney King riots-late April 1992 M/F dipped significantly in August 1992, 4months after the riots (p=0.044). Breivik Shooting-22/07/2011 M/F dipped significantly in December 2011, 5months after the event (p=0.004). Sandy Hook Shooting-14/12/2012 M/F dipped significantly in April 2013, 4months after the event (p=0.009).Discussion: M/F dips follow catastrophic or tragic events if these are felt to be momentous enough by a given population. All of the above events caused significant population stress. The M/F dips noted may have been caused by population stress which is known to lead to the culling of frail/small male foetuses. The dips noted are comparable to a substantial proportion of quoted values for perinatal mortality, potentially elevating this a public health issue.Key Guidelines: 1. The male-to-female ratio at birth is decreased by stressful events. 2. This is due to an excess of male foetal losses in established pregnancies. 3. Such losses in response to acute events are transient. 4. This ratio may be a useful indicator of population stress. RESEARCH DIRECTIONS: 1. Gender ratios in populations could be routinely monitored in order to assess the impact of stressful events that may reduce the male-to-female birth ratio. [ABSTRACT FROM AUTHOR]

Humans infected with the parasite Toxoplasma gondii display a wide variety of abnormal behaviours, from suicide and depression to stuttering. These behaviours have been seen as so serious as to constitute a public health problem. It is not clear to what extent the parasite is a cause of, or merely a marker for, these behaviours, but there is evidence for both. Some of these behaviours are associated with changes in steroid hormones, that is, estrogen in women and testosterone in men. It is suggested here that these endocrine-related states of infected people may be better understood by studying their offspring sex ratios. [ABSTRACT FROM AUTHOR]

Introduction The male to female ratio of live births is expressed as the ratio of male live births divided by total live births (M/T). Factors which reduce M/T include toxins, stress and privation. Britain remains enamoured of the Monarchy. This study was carried out in order to ascertain whether Royal events influenced M/T in the UK. Materials and methods Live births were analysed in relation to the birth of Prince Charles (1948), the Coronation of Queen Elizabeth II (1952), the Silver Jubilee (1977), the wedding of Diana Spencer to Charles, Prince of Wales (July 1981), the birth of Prince William (1982), the death of Lady Diana (August 1997), the wedding of Kate Middleton to Prince William (2011) and the Golden Jubilee (2002). Results This study analysed 29,293,240 live births. There was a significant dip in M/T in the Coronation year ( p = 0.03). M/T dipped significantly in relation to the Royal Wedding, commencing a year before ( p < 0.0001). There were no significant M/T changes in relation to the Silver and Golden Jubilees. The birth of Prince William in 1982 resulted in a rise in M/T in the following year only ( p = 0.016). Analysis by quarter in relation to Lady Diana's death showed a decline in M/T 4–5 months later in the first quarter of 1998 ( p = 0.046). Comments The anticipation and stress leading to the Coronation and Royal Wedding may have depressed M/T. Increased coital rates associated with exuberance in relation to Prince William's birth may have raised M/T. Lady Diana's death was temporally associated with a decline in M/T. Royalty events may affect M/T ratios in Britain. [ABSTRACT FROM AUTHOR]

Objective: Male live births slightly exceed female live births by approximately 3%. The ratio of male to total live births is conventionally represented as M/F. Many factors have been shown to affect M/F, mainly privation, toxins, and stress, all of which reduce M/F. Population stress may be engendered by natural phenomena such as earthquakes and man-made events such as short wars, terrorist attacks, and contracting economies. This study was conducted to ascertain whether the onset of the "Great Recession" (2007) was associated with changes in M/F in the United States (US). Material and Methods: Annual monthly live births by gender for January 2006 to December 2008 were obtained from United States Centres for Disease Control and Prevention. Results: In 2007, there were 4316233 live births [M/F: 0.51157; 95% confidence intervals: 0.51110-0.51205). M/F rose between January and June, and then fell sharply between August and December. M/F was statistically significantly lower in the second half of 2007 (p=0.007). The dip in M/F from June to July was also significant (p=0.02). These findings were not replicated in the amalgamated data for 2006 and 2008. Conclusion: The United States housing boom of the mid-2000s was fueled by rising house prices and cheap mortgages given to credit-poor buyers. A halt in rising house prices resulted in defaults and foreclosures, triggering the worst financial crisis since the Great Depression. The associated stress appears to have decreased M/F in the US. [ABSTRACT FROM AUTHOR]

Background Secular trends have been found in the male–female ratio at birth (M/F: male births divided by total births) in various countries, and this ratio is anticipated to approximate 0.515. Births in Dragon years are considered auspicious. Fertility is known to have increased in Dragon years in Hong Kong. This study analyzed M/F with reference to Dragon years. Methods Annual national data for male and female live births in Hong Kong were obtained from the World Health Organization and analyzed with contingency Tables. Results There were 3,827,347 live births (1960–2009). Births declined steadily, then increased from 2004 in association with M/F. M/F was stable prior to this time, with spikes in 1975–1976, 1988, and 2000, associated with increases in births for these same years. Conclusion M/F follows a U-shaped regression on cycle day of insemination. Families attempting to conceive children during Dragon years may have increased coital rates, inadvertently skewing M/F in favor of a male excess. [ABSTRACT FROM AUTHOR]

Introduction: Males are usually born in excess of females and the ratio of male births to female births is conventionally referred to as M/F. Many factors, including stress, privation and natural disasters are associated with a lowering of M/F. Malta has a North-South divide, with a more affluent North as opposed to a more industrialised and less prosperous South. This study was carried out in order to ascertain whether regional economic differences influenced M/F in Malta. Methods: Births by gender, year of birth and locality from 1999 to 2013 were subdivided into ten regions in a geographic distribution devised by the Department of Health Information and Research. Regions were also amalgamated into two groups of five which represented North-West and South-East Malta. The island of Gozo was considered separately. Results: There were no statistically significant differences in M/F between the ten regions nor between North-West, South-East and Gozo regions. There were no significant secular trends in M/F in these regions. Discussion: M/F declines under adverse environmental factors (including economic stress) but despite the overall poorer economic circumstances in the South of the Island, this study failed to show a significant difference in M/F by region. This may be due at least in part to the relatively small numbers involved. Alternatively, the purported socio-economic differences may not have been sufficiently large so as to skew M/F to statistically significant levels. [ABSTRACT FROM AUTHOR]

AIMS: Fallout from atomic bomb testing may travel great distances before precipitating. Males are born in excess of females in a ratio that approximates 0.515 (M/T: male live births divided by total live births. Radiation increases M/T by causing lethal malformations that affect female more than male foetuses, decreasing total births. This study was carried out in order to ascertain whether the effects of increased background radiation levels from atomic weapon testing had any widespread effects on M/T and births in the Americas, Europe, Asia and Australasia in relation to the Partial Test Ban Treaty of 1963. METHODS: Annual live births by gender were obtained from a World Health Organization dataset and annual number of atomic bomb tests were also obtained (historical data). RESULTS: Overall, 94.5% of births studied showed a uniform reduction in M/T between the early 1950s to the late 1960s, followed by an increase to the mid-1970s, with a subsequent decline. A negative correlation of M/T with total births was found in 66% of births studied, and these were the regions which exhibited the rising M/T pattern in the 1970s. The birth deficit for countries with significant correlations of total births with M/T (North America, Europe and Asia) was estimated at 10090701. CONCLUSIONS: A rising M/T was found in most regions in temporal association with atomic weapon testing. Most of these regions also had an associated decline in total births. Elevated levels of man-made ambient radiation may have reduced total births, affecting pregnancies carrying female pregnancies more than those carrying male pregnancies, thereby skewing M/T toward a higher male proportion. [ABSTRACT FROM AUTHOR]

Introduction: Male live births occur slightly in excess of female. This ratio is expressed as M/F. Terrorist attacks induce stress which transiently lowers M/F three to five months later due to increased male foetal losses. A previous study had shown that the assassination of President John F. Kennedy in November 1963 was associated with a significant dip in M/F in the United States for 1964 due to a dip confined to March 1964. This study was carried out in order to ascertain whether the assassination influenced M/F in the rest of the world.Methods: Annual male and female live births were obtained from a World Health Organisation Mortality database for all countries reporting. Comparisons were made between 1964, the year after the assassination, and the preceding five years (1959-1963) and following five years (1965-1969). Monthly data was only available for Malta, for the period 1958-1968.Results: There were 159,339,564 live births (82,066,005 males, 77,273,559 females, M/F 0.5150; 95% CI 0.5150-0.5151). No dip was present for 1964 for any country, nor for the amalgamation of European countries, for the Far East, the North American continent, or for the amalgamation of the total. Data for Malta showed a significant decline in March 1964 (M/F 0.4661, p=0.0175), translating to a loss of 56 boys (estimated at 6.3/1000 births).Discussion: These findings replicate the findings for the United States following the assassination of President Kennedy. The March M/F dip transiently exceeded the modern expected rate for perinatal mortality, making terrorist attacks Public Health issues. [ABSTRACT FROM AUTHOR]

The term gendercide was first coined in 1985 and refers to the deliberate extermination of persons of a particular sex.1 The notion and its potential consequences had been conceived as far back as 1793, when the Marquis Nicolas de Condorcet had speculated "what might be [the effect] on humankind [of] the discovery of a means of producing a male or female child according to the will of the parents [...]. Supposing that this is likely to become a common practice, [...] would it [not] lead to [changes] in the social relations of human beings, whose consequences could be harmful to the peaceable development of that indefinite perfectibility with expectations of which we have flattered humankind?"2 Due to the patriarchal nature of most human societies, the extermination of females is a far commoner occurrence than the extermination of males. Male preference resulting in a higher proportion of males at all ages, particularly in Asia, has been attributed to the Confucian patriarchal tradition that is characterised by strong son preference and female subordination.3 [ABSTRACT FROM AUTHOR]

AIMS: The Windscale (UK) fire of 1957 carried radioactive fallout according to the then prevailing wind patterns, in a North-Easterly direction across the Nordic countries, toward Norway. The male:female ratio at birth (M/F) is known to be increased after parental exposure to ionising radiation due to foetal losses that affect female more than male pregnancies. This study was carried out in order to ascertain whether the Windscale fire had any effects on M/F and birth rates in the United Kingdom and Scandinavia. METHODS: Annual live births by gender were obtained from a World Health Organization dataset. The null hypothesis was that there were no significant changes in M/F or in births in temporal association with the 1957 Windscale event in abovementioned countries. RESULTS: There were no significant effects on the UK and most of Scandinavia but there was a significant rise in M/F for Norway and Finland with an aggregate deficit of around 4000 births in each country. CONCLUSIONS: A recent study suggests that the plume from the reactor extended further east than previously believed. This study confirms that contamination from the Windscale fire had a negligible impact on the UK (as measured by birth effects) but had a significant impact on births in Norway and Sweden. [ABSTRACT FROM AUTHOR]

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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

Introduction: The male to female ratio of live births is expressed as the ratio of male live births divided by total live births (M/F). Although this would be more accurately abbreviated as M/T (male births divided by total births), it is widely (albeit technically incorrectly) abbreviated as M/F, and this will be used throughout. Globally, over the past four decades, this is expected to be 0.515, with a slight (1.5%) male excess. M/F exhibits an unexplained contrasting latitude gradient. More males are born towards the south of Europe, and the south of Asia, while more males are born toward the north in North American continent. M/F is also declining overall, in both of these continents. This study investigates secular trends and latitude gradients in M/F in Australia and New Zealand from a World Health Organization (WHO) dataset that includes the past sixty years. Methods: Permission was obtained to source WHO datasets going back to 1950, following which Microsoft Excel was used to calculate M/F ratios. Australian and New Zealand data were available for the years 1950-2006 and 1950-2009 respectively. Chi tests for trend were used for annual male and female births. These were performed using the Bio-Med-Stat Excel add-in for contingency tables. Results: There were 17035325 births for Australia and New Zealand during this period. M/F ratios ranged between 0.507-0.519. No latitude variations in M/F were found between Australia (9° to 44°) and New Zealand (29° to 53°). The overall M/F was 0.5134 - lower than the anticipated 0.515, with an estimated male birth deficit of 28009. Cycles of 30 years duration are apparent in the dataset but not at statistically significant levels. Discussion: The lack of latitude gradient in this region is not unexpected as there is a wide latitude overlap between Australia and New Zealand. It has been hypothesised that M/F exhibits a 30 year cycle due to an unknown mechanism that negatively correlates M/F with the adult sex ratio at the time of conception. Conclusion: The factor/s that are causing a decline in M/F ratios in Europe, North America and Asia are absent or not so strongly influential in Australasia. [ABSTRACT FROM AUTHOR]

Introduction: Males are born usually in excess of females and the ratio is often expressed as M/T (male divided by total births). Many acute and stressful factors have been shown to influence M/T, and these transiently lower M/T for a one month period, three to five months after such events. This study was carried out in order to ascertain whether the Las Vegas shooting (10/2017) and the Hawaii false missile alert (01/2018) influenced M/T in the respective populations.Methods: Monthly live births by gender for the states of Nevada and Hawaii for 2016-2018 were obtained from the website of the Centers for Disease Control and Prevention (CDC).Results: There were no significant dips in M/T for any of the relevant months (3-5 months) following these events.Discussion: Research to date has shown M/T dips following catastrophic or tragic events. Equivalent dips were not noted in this study. The reasons for this may be one or a combination of the following. The population size was not sufficiently large in order to detect an M/T dip. Alternatively, the events were not felt to be sufficiently momentous by the populace such that an M/T dip was not produced. Yet another possibility is that these particular populations are somehow hardier and more resistant to such influences. Not all acute events may result in a visible/significant reduction in M/T. [ABSTRACT FROM AUTHOR]

Introduction: The human sex ratio or sex odds at birth (M/F) are influenced by many factors. Radiation is the only stressor known to elevate the ratio while dropping total births. The Mainz research nuclear reactor (FRMZ) underwent extensive refurbishment commencing in 1992 and with further upgrading in 2011. This study was carried out in order to investigate any possible effects of these events on M/F.Methods: Annual municipality-specific births by sex were obtained from official government sources. Statistical methods used included ordinary linear logistic regression and Poisson regression.Results: M/F rose significantly in 1993 only close to the FRMZ (<10 km) with sex odds ratio (SOR) 1.023 (p = 0.0074) and this rise was associated with numerically equivalent drops in male births of 4.01% (p = 0.0251) and female births of 6.17% (p = 0.0005). No such effects were seen beyond 10 km.Discussion: These findings add to the corpus of evidence that man-made radiation may have significant effects on total births and on M/F with a skew toward male births. While the authors are certain that suitable precautions were taken when the reactor in Mainz was handled, the findings imply that these may not have been sufficient. Perhaps even greater care and even more stringent precautions need to be employed when dealing with radioactive elements. It clearly behoves humanity to exercise extreme caution when handling, processing, and storing radioactive materials and waste. [ABSTRACT FROM AUTHOR]

This second of two Best Practise Guidelines will continue to explore facets pertaining to factors that influence the sex ratio at birth (M/F). The papers include a quantitative study in the United States, investigating the effects of Thanksgiving Day, Christmas Day and Valentine's Day on M/F (which rises). A second paper is devoted to the factor that most influences M/F worldwide: male offspring preference. The third paper focusses on radiation which appears to be the only toxin/stressor that increases M/F by culling female in excess of male foetuses. The paper investigates the effects of the Mainz research nuclear reactor in Germany. Yet another paper reviews seasonality of M/F. Two more theoretical papers discuss the significance of low M/F of offspring and of siblings of probands with systemic lupus erythematosus or rheumatoid arthritis, implicating a common role for testosterone. In yet another paper, high levels of maternal first-trimester intrauterine testosterone are also implicated in male sex, autism, gender dysphoria and non-right-handedness. Finally, a paper reviews the effects of toxoplasmosis on M/F since may be one of the most important environmental factors on this ratio. It is hoped that this second set of papers will further provide stimulation and provocation for research on this intriguing topic. [ABSTRACT FROM AUTHOR]

This paper reviews the classical theories that attempted to explain the influences on the sex ratio at birth (M/F). These included notions pertaining to the four elements (earth, air, fire and water) and to laterality i.e. from which side of the body (in both parents) the conceptual principle arose. This narrative will also outline the initial physical measurements of male and female births and speculations by John Graunt (1620-1674), John Arbuthnott (1667-1735) and Johann Süssmilch (1707-1767), as well as the conundrums that M/F presented to Charles Darwin (1809-1882) and the theories of Ronald Fisher (1890-1962) who expanded on concepts first promulgated by Nicolas de Caritat, Marquis de Condorcet (1743-1794). Fortunately, the thousands of papers generated on topic, especially the more recent work pertaining to direct and measurable influences (such as exogenous stress periconceptually and during pregnancy) have begun to yield some concrete findings, indeed, "among this welter of evidence, it is possible to pin down a few facts" such that "we have found ourselves following Ariadne's thread to a series of clues that bind the calculation of the proportion of boys and girls at birth". [ABSTRACT FROM AUTHOR]

Introduction: The sex ratio at birth (male divided by total births: M/F is often quoted as approximating 0.515. Many factors have been shown to influence this ratio, and these include both acute events and chronic circumstances, both of which may be man-made or natural. This study was carried out in order to attempt to narrow down the range for M/F from a large and internationally recognised dataset of countries reporting live births to the World Health Organisation (WHO).Methods: Male and female live births were obtained from a WHO (Health for All - HFA) database for the five year period 1996-2000, for all countries reporting to WHO, and for which these values were reported.Results: This study analysed 88,875,750 live births. M/F is estimated at 0.5147 (95% CI: 0.5146-0.5148), quite close to the widely quoted value of 0.515.Discussion: M/F may be less due to female foeticide which cannot be accurately assessed, an unavoidable limitation. Other limitations for M/F estimates such as these are broad, cyclic secular variations, broad demographic population changes, chronic stress and an overall declining M/F in industrialised countries. [ABSTRACT FROM AUTHOR]