Reduced male births in major Italian cities

Qualitative approximations to causality: Non-randomizable factors in clinical psychology

Background

Causal quests in non-randomized studies are unavoidable just because research questions are beyond doubt causal (e.g., aetiology). Large progress during the last decades has enriched the methodical toolbox.

Aims

Summary papers mainly focus on quantitative and highly formal methods. With examples from clinical psychology, we show how qualitative approaches can inform on the necessity and feasibility of quantitative analysis and may yet sometimes approximate causal answers.

Results

Qualitative use is hidden in some quantitative methods. For instance, it may yet suffice to know the direction of bias for a tentative causal conclusion. Counterfactuals clarify what causal effects of changeable factors are, unravel what is required for a causal answer, but do not cover immutable causes like gender. Directed acyclic graphs (DAGs) address causal effects in a broader sense, may give rise to quantitative estimation or indicate that this is premature.

Conclusion

No method is generally sufficient or necessary. Any causal analysis must ground on qualification and should balance the harms of a false positive and a false negative conclusion in a specific context.

The human sex ratio at birth and late fetal mortality: the Italian case

This study explores the short-term relationships between sex ratio at birth and late fetal mortality in Italy from 1910 to 2016. As the leading scholars' attention traditionally focused on long-term trends and variations in the sex ratios at birth among different populations, less interest regarded short-term fluctuations as they were mainly seen as an effect of random variability. We detrended the national series of males proportion among live births and stillbirths by their medium-term component to consider the annual deviations from a normal trend. After controlling for fertility tendencies and wars effects, regression models seem to show the effects of stillbirth on the proportion of male newborns. A sensitivity analysis was also carried out to assess the effects of the perinatal deaths on the proportion of males at birth, combining stillbirths and early neonatal losses to control the possible misspecification between stillborn infants and early neonatal deaths. The significance of late fetal mortality reflects the mortality excess among male fetuses during the intrauterine life, showing evidence for the in utero hypothesis selection.

Bayesian Inference on Predictors of Sex of the Baby

It is well known that the sex ratio at birth is a biological constant, being about 106 boys to 100 girls. However couples have always wanted to know and decide in advance the sex of a newborn. For example, a large number of papers appeared connecting biometrical variables, such as length of follicular phase in the woman menstrual cycle or timing of intercourse acts to the sex of new baby. In this paper, we propose a Bayesian model to validate some of these theories by using an independent database. Results show that we could not show an effect of the follicular length on the sex of the baby. We also obtain a slightly larger probability, although not significant, of conceiving a female just after the mucus peak day.

Exposure to widespread environmental endocrine disrupting chemicals and human sperm sex ratio

In recent years, a trend toward a declining proportion of male births has been noted in several, but not all, industrialized countries. The underlying reason for the drop in the sex ratio is unclear, but one theory states that widespread environmental endocrine disrupting chemicals affecting the male reproductive system in a negative manner could be part of the explanation. The present study was designed to investigate whether the urinary phthalate, pyrethroids and polycyclic aromatic hydrocarbons metabolites concentrations were associated with sperm Y:X ratio. The study population consisted of 194 men aged under 45 years of age who attended infertility clinic in Lodz, Poland for diagnostic purposes with normal semen concentration of 20-300 mln/ml or with slight oligozoospermia (semen concentration of 15-20 mln/ml) (WHO, 1999). The Y:X ratio was assessed by fluorescent in situ hybridization. Urinary concentrations of 1-hydroxypyrene were measured by high performance liquid chromatography, phthalate metabolites were analyzed using a procedure based on the LC-MS/MS methods and metabolites of synthetic pyrethroids were assessed by gas chromatography ion-tap mass spectrometry method. After adjustment for potential confounders (past diseases, age, abstinence, smoking, alcohol consumption, sperm concentration, motility, morphology) 5OH MEHP, CDCCA to TDCCA and 1-OHP was negatively related to Y:X sperm chromosome ratio (p = 0.033, p < 0.001, p = 0.047 respectively). As this is the first study to elucidate the association between the level of metabolites of widespread environmental endocrine disrupting chemicals (phthalates, synthetic pyrethroids, polycyclic aromatic hydrocarbons) on sex chromosome ratio in sperm therefore, these findings require further replication in other populations.

Secular trends and geographical variations in sex ratio at birth

Numerous studies have established the presence of secular trends and geographical variations in sex ratio at birth, albeit with mixed and often contradictory results. In addition, a multitude of environmental, social, economic, demographic and other factors has been proposed to influence the sex ratio at birth, thus complicating the interpretation of both secular trends and geographical variations. In this paper, the current state of knowledge on these issues is presented and critically assessed. Analyzing longer time series of sex ratio at birth with possible cycles and random components is given priority over establishing simple linear trends in the data. In analyzing the geographical variation in the sex ratio at birth, two different levels of analysis are distinguished (global and local), and two different sets of factors affecting the sex ratio at birth are proposed accordingly. Some key guidelines and future research directions are also proposed.

Sperm counts and sperm sex ratio in male infertility patients

In recent years, investigators have noted a trend toward a declining proportion of male births in many industrialized nations. While men bear the sex-determining chromosome, the role of the female partner as it pertains to fertilization or miscarriage may also alter the gender ratio. We attempted to determine a man's secondary sex ratio (F1 generation) by directly examining the sex chromosomes of his sperm. We examined our male infertility clinic database for all men who had undergone a semen fluorescence in situ hybridization (FISH). Patient demographic and semen parameters were recorded. Chi-squared analysis was used to compare gender ratios (Y chromosomes/total chromosomes). Multivariable logistic regression was used to predict the odds of possessing a Y-bearing sperm after accounting for demographic and semen parameters. A total of 185 men underwent sperm FISH. For the entire cohort, the proportion of Y chromosome-bearing sperm was 51.5%. Men with less than five million motile sperm had a significantly lower proportion of Y chromosome-bearing sperm (50.8%) compared to men with higher sperm counts (51.6%; P=0.02). After multivariable adjustment, a higher sperm concentration, total motile sperm count and semen volume significantly increased the odds of having a Y chromosome-bearing sperm (P<0.01). As a man's sperm production declines, so does the proportion of Y chromosome-bearing sperm. Thus, a man's reproductive potential may predict his ability to sire male offspring.

Effects of in utero JP-8 jet fuel exposure on the immune systems of pregnant and newborn mice

The US Air Force has implemented the widespread use of JP-8 jet fuel in its operations, although a thorough understanding of its potential effects upon exposed personnel is unclear. Previous work has reported that JP-8 exposure is immunosuppressive. In the present study, the effects of in-utero JP-8 jet fuel exposure in mice were examined to ascertain any potential effects of jet fuel exposure on female personnel and their offspring. Exposure by the aerosol route (at 1000 mg/m3 for 1 h/day; similar to exposures incurred by flight line personnel) commencing during the first (d7 to birth) or last (d15 to birth) trimester of pregnancy was analyzed. It was observed that even 6-8 weeks after the last jet fuel exposure that the immune system of the dams (mother of newborn mice) was affected (in accordance with previous reports on normal mice). That is, thymus organ weights and viable cell numbers were decreased, and immune function was depressed. A decrease in viable male offspring was found, notably more pronounced when exposure started during the first trimester of pregnancy. Regardless of when jet fuel exposure started, all newborn mice (at 6-8 weeks after birth) reported significant immunosuppression. That is, newborn pups displayed decreased immune organ weights, decreased viable immune cell numbers and suppressed immune function. When the data were analyzed in relation to the respective mothers of the pups the data were more pronounced. Although all jet fuel-exposed pups were immunosuppressed as compared with control pups, male offspring were more affected by jet fuel exposure than female pups. Furthermore, the immune function of the newborn mice was directly correlated to the immune function of their respective mothers. That is, mothers showing the lowest immune function after JP-8 exposure gave birth to pups displaying the greatest effects of jet fuel exposure on immune function. Mothers who showed the highest levels of immune function after in-utero JP-8 exposure gave birth to pups displaying levels of immune function similar to controls animals that had the lowest levels of immune function. These data indicated that a genetic component might be involved in determining immune responses after jet fuel exposure. Overall, the data showed that in-utero JP-8 jet fuel exposure had long-term detrimental effects on newborn mice, particularly on the viability and immune competence of male offspring.

Relationship between urinary estrogen levels before conception and sex ratio at birth in a primate, the gray mouse lemur

BACKGROUND

In primates, including humans, bias of sex ratio at birth has been reported to depend on maternal condition at conception. In a Malagasy primate, the gray mouse lemur, male-biased sex ratio at birth occurred in captive parous females. The male bias was previously demonstrated to be pre-conceptual and independent of the female's nutritional state. It was hypothesized to be related to changes in hormonal state at ovulation.

METHODS AND RESULTS

The relationship between urinary estradiol (E2) levels during the follicular phase until estrus and litter production (number and sex of newborns) was assessed in 91 females mated under controlled conditions. Changes in E2 levels prior to ovulation followed the typical primate pattern characterized by a gradual rise during the 10 days preceding the sharp increase at estrus. A clear decline in E2 levels occurred with ageing. Direction of the sex ratio bias was unrelated to E2 levels at ovulation time but was significantly dependent on E2 levels during the follicular phase. Reduced E2 levels prior to estrus led to male-biased litters.

CONCLUSION

This study suggests that hormonal stimulation during the follicular phase plays a role in shifting sex ratio at conception through changes in the local environment of the ova. This hypothesis deserves testing by assessing estrogen levels throughout the follicular phase in other primate species including humans.

Secular trends in uncertain-sex births and proportion of male births in Norway, 1967-1998

It has been hypothesized that environmental factors influence sex differentiation in the fetus, thus causing a reduced sex ratio (male/female) at birth, an increase in the prevalence of ambiguous-sex infants, and possibly an increase in spontaneous abortion rates. In Norway, subsequent to 1967, all deliveries, including late abortions after 16 wk of gestation, have been reported to the Medical Birth Registry of Norway. The authors used these data to assess birth-weight-specific secular trends of uncertain-sex infants and the proportion of male births, from 1967 through 1998. Total rates of uncertain-sex infants increased from 2.3/10,000 births in 1967 to 8.0/10,000 births in 1998 in the birth weight strata of less than 600 gm. The total proportion of male births was stable; however, there was a reduction in the proportion of male births among births weighing less than 400 gm--from 58.4% to 53.4%. Incomplete ascertainment of abortions may have biased the results, but it would not have accounted for the increased occurrence of uncertain-sex infants and the decreased proportion of males observed among late-term abortions.

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.

Environmental factors and the proportion of males at birth in Italy

A significant decline in the proportion of male births has been observed in recent decades in several western countries, and several researchers have raised the question of the possible role of environmental pollution in this trend. In the present analysis, the authors examined the effect of environmental factors (pollution from pesticides, urban pollution, and industrial pollution) on the sex ratio (proportion of males) of Italian singleton 1st births for the years 1989-1993, controlling for the age of the mother. The data show a slight increase in the sex ratio from north to south; however, no reduction in the proportion of males was seen in areas with higher pesticide consumption or intense industrial pollution. A small reduction in sex ratio was found in the major urban centers. The analysis was based on individual information on birth order and maternal age, as well as on ecological data on environmental pollution. No significant association was found between environmental pollution and the proportion of male births in Italy during the study period.

Potential effects of certain persistent organic pollutants and endocrine disrupting chemicals on the health of children

Persistent organic pollutants are lipophilic, man-made chemicals that are highly resistant to degradation. Due to their persistence, they have become distributed in small quantities throughout the world. They bioaccumulate in thefood chain and are stored in fatty tissues. Biomagnifications up the food chain result in potential widespread human exposure to these chemicals. Exposure to persistent organic pollutants has been associated with many adverse human health effects, including impaired neurodevelopment, immune and reproductive function. Many persistent organic pollutants also possess the ability to disrupt the normal functioning of the endocrine system. There is an increasing concern that low-level exposure to these endocrine disrupting chemicals may have adverse health impacts, particularly during fetal, neonatal, and childhood development. Both the nature and severity of health outcomes may depend on the developmental time-period during which chemical exposure occurs. This report summarizes scientific evidence on health effects of low-level exposure to persistent organic pollutants and endocrine disrupting chemicals.

Reproductive outcomes in the women of the Red River Valley of the north. I. The spouses of pesticide applicators: pregnancy loss, age at menarche, and exposures to pesticides

In the current study, there was a modest but significant increase in risk (1.6- to 2-fold) for miscarriages and/or fetal loss occurring throughout the year in the spouses of applicators who use fungicides. There is a surprisingly significant deficit in the number of male children born to the spouses of fungicide applicators. First-trimester miscarriages occur most frequently in the spring, during the time when herbicides are applied. Use of sulfonylurea (odds ratio OR = 2.1), imidizolinone (OR = 2.6) containing herbicides, and the herbicide combination Cheyenne (OR = 2.9) by male applicators was statistically associated with increased miscarriage risk in the spring. Limited survey data from women who are the spouses of applicators did not show major alterations of long-term endocrinologic status (menarche, menopause, endometriosis). With regard to personal pesticide exposures, only women who engaged in pesticide application where there is direct exposure to these products are at demonstrable risk (OR = 1.8) for miscarriage. It was hypothesized that the overall reproductive toxicity observed in this population is, for the greater part, a male-mediated event. Clarification of exposure events leading to reproductive toxicity through direct measurements of exposure in both men and women is needed to resolve this issue.

Paternal concentrations of dioxin and sex ratio of offspring

BACKGROUND

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD or dioxin), is commonly considered the most toxic man-made substance. We have previously shown that high serum concentrations of TCDD in parents from Seveso, Italy, were linked to their having a relative increase in the number of female births after the parents exposure to a release of dioxin in 1976. We have continued the study to determine whether the parents' sex and/or age at exposure affected the sex ratio of their children.

METHODS

We measured the TCDD concentrations in serum samples from potentially exposed parents collected in 1976 and 1977, and investigated the sex ratio of their offspring.

FINDINGS

Serum samples were collected from 239 men and 296 women. 346 girls and 328 boys were born to potentially exposed parents between 1977 and 1996, showing an increased probability of female births (lower sex ratio) with increasing TCDD concentrations in the serum samples from the fathers (p=0.008). This effect starts at concentrations less than 20 ng per kg bodyweight. Fathers exposed when they were younger than 19 years of age sired significantly more girls than boys (sex ratio 0.38 [95% CI 0.30-0.47]).

INTERPRETATION

Exposure of men to TCDD is linked to a lowered male/female sex ratio in their offspring, which may persist for years after exposure. The median concentration of dioxin in fathers in this study is similar to doses that induce epididymal impairments in rats and is about 20 times the estimated average concentration of TCDD currently found in human beings in industrialised countries. These observations could have important public-health implications.