Effects of maternal birth season on birth seasonality in the Canadian population during the seventeenth and eighteenth centuries

Birth records of the French-Canadian population for the period 1621-1765 were analyzed retrospectively to examine the effect of maternal birth season on the seasonal distribution of births. Preliminary examination indicated that there was a bimodal pattern in birth seasonality: a major peak in early spring, a trough in early summer, a minor peak in autumn, and a trough around December. Because this seasonality was strongly biased at the level of the first birth by the month of marriage, which was concentrated in November, the seasonality of nonfirst births (n = 32,926) was examined in relation to the four seasons of maternal birth. Mothers born in May-July showed a flatter monthly distribution of nonfirst births at a maternal age of 28 years or more. Analysis of marriage-first birth intervals indicated that mothers who married in August-October showed a lower percentage of immediate conception (intervals of 8-10 months), whereas those mothers born in May-July had a higher percentage of immediate conception. This difference in birth seasonality shown by mothers born in May-July is similar to results from early twentieth-century Japan. Some seasonal infertility factors could have affected the embryos at the earliest stage of pregnancy, modifying a part of the seasonal variation in birth rate.     

Paternal effects on the human sex ratio at birth: evidence from interracial crosses

The effects of interracial crossing on the human sex ratio at birth were investigated using United States birth-certificate data for 1972-1979. The sex ratio was 1.059 for approximately 14 million singleton infants born to white couples, 1.033 for 2 million born to black couples, and 1.024 for 64,000 born to American Indian couples. Paternal and maternal race influences on the observed racial differences in sex ratio were analyzed using additional data on approximately 97,000 singleton infants born to white-black couples and 60,000 born to white-Indian couples. After adjustment for mother's race, white fathers had significantly more male offspring than did black fathers (ratio of sex ratios [RSR] = 1.027) and Indian fathers (RSR = 1.022). On the other hand, after adjustment for father's race, white mothers did not have more male offspring than did black mothers (RSR = 0.998) or Indian mothers (RSR = 1.009). The paternal-race effect persisted after adjustment for parental ages, education, birth order, and maternal marital status. The study shows that the observed racial differences in the sex ratio at birth are due to the effects of father's race and not the mother's. The study points to paternal determinants of the human sex ratio at fertilization and/or of the prenatal differential sex survival.     

Patterns of low birth weight in the Bengali newborns

This paper examines the distribution of low birth weight (2500 g or less) by gestation time, sex, maternal age, parity (birth order), socioeconomic conditions, and season of birth among 5117 single live births born to Bengali mothers at the Ramakrishna Mission Seva Pratisthan Hospital in Calcutta, India. Preterm infants have low birth weight significantly more often than their full term counterparts. Female infants have low birth weights significantly more often than male infants. The infants of poor mothers have lower birth weights in higher order births more often than infants of higher orders born to well-off mothers. Teenaged mothers produce low birth weight babies significantly more often than older mothers. Although the relationship is not significant, low birth weight infants occur more often among 1st and late born infants and less often among 2nd born infants. The season of birth is not significantly associated with birth weight. Less than 10% of low birth weight infants are pre-term, while the rest are full term. The great majority of low birth weight infants are small-for-gestational-age; the minority are small due to curtailed gestational age. The proportion of infants weighing less than 2001 g is only 9%; this figure tallies closely with earlier studies of India.     

Factors associated with exclusive breastfeeding at discharge during the COVID-19 pandemic in 17 WHO European Region countries

Both the consumption of breastmilk in infancy and a person’s season of birth influences his or her health, educational, professional, and behavioral outcomes. Further, season of birth effects differ by sex. However, current research, for the most part, neglects to examine if season of birth and breastfeeding are related. This paper examines the impact of sex-based variations in season of birth on breastfeeding likelihood and duration in the U.S. Using data from children born to female respondents of the National Longitudinal Survey of Youth 1979 (born between 1970 and 2012), this study examines with Probit, Negative Binomial, and Ordinary Least Squares (OLS) regressions if a child’s season of birth and sex are correlated with breastfeeding incidence and duration. The breastfeeding incidence and duration data are self-reported by the mother. Season of birth has a small but statistically significant impact on the incidence and duration of breastfeeding, which varies depending on the sex of the infant. Mothers giving birth to sons in the spring are 13.5% less likely to breastfeed than those giving birth to sons in the winter (with a p - value of 0.0269). Mothers with daughters born in the summer or fall (autumn) breastfeed slightly longer than mothers with daughters born in the spring. On average, mothers of summer-born daughters breastfeed 4.1% longer (with a 95% confidence interval of 0.3 - 7.8) and those with fall-born daughters 3.8% longer (with a 95% confidence interval of 0 - 7.5). Mothers giving birth to daughters in the spring are also significantly less likely to reach the breastfeeding six-week duration target (compared to fall and winter births) and the one-year duration target (compared to fall births). These findings suggest that the costs and benefits of breastfeeding an infant vary with the season of birth and the sex of the child. This finding could explain some of the season of birth effects previously identified in the literature. Further, policymakers seeking to increase breastfeeding rates should consider the reduced breastfeeding rates and durations for children born in the spring.     

Maternal and neonatal factors influencing premature birth and low birth weight in Australia

This study identified the influences of neonatal and maternal factors on premature birth and low birth weight in New South Wales, Australia. Bivariate and multivariate analyses were used to explore the association of selected neonatal and maternal characteristics with premature birth and low birth weight. The findings of this study showed that premature birth and low birth weight rate significantly varied by infant sex, maternal age, marital status, Aboriginality, parity, maternal smoking behaviour during pregnancy and maternal hypertension. First-born infants, and infants born to mothers aged less than 20 years, or who were single, separated/divorced, Aboriginal or who smoked during the pregnancy, were at increased risk of being premature or of low birth weight. This study also found that risk factors for premature births and low birth weight were similar in both singleton and multiple births. Gestational age was confirmed to be the single most important risk factor for low birth weight. The findings of this study suggest that in order to reduce the incidence of low birth weight and premature births, health improvement strategies should focus on anti-smoking campaigns during pregnancy and other healthcare programmes targeted at the socially disadvantaged populations identified in the study.     

Variation of sex ratio and ABO blood group composition by month of birth of blood donors in Tokyo

Sex ratio of 17,273 blood donors born during the period between 1925 and 1935 was examined according to their month of birth and ABO blood groups in comparison with 5,810 healthy non-blood donors born in the 1900s to 1930s. The sex ratio of the blood donors and the non-blood donors varied similarly according to their month of birth with a prominent peak in summer births and a trough in winter births. This birth season with a high sex ratio was different from that of the general births during the period between 1921 and 1935, in which a maximum sex ratio was found in November. A possible explanation for the difference is the different rate of male and female infant deaths according to birth month. Variation of the sex ratio according to season of birth was not similar among the four ABO blood groups. Sex ratio of the donors with blood group B showed no elevation among the summer births. Non-blood donors with blood group B, on the contrary, showed a higher sex ratio than the others in the summer births. This difference can not be explained by infant or juvenile deaths. A possibility is that a tendency to become a blood donor is modified by the season of one's birth differently according to gender and ABO blood groups.     

Season of birth affects juvenile survival of giraffe

Variation in timing of reproduction and subsequent juvenile survival often plays an important role in population dynamics of temperate and boreal ungulates. Tropical ungulates often give birth year round, but survival effects of birth season for tropical ungulate species are unknown. We used a population of giraffe in the Tarangire Ecosystem of northern Tanzania, East Africa to determine whether calf survival varied by season of birth. Variation in juvenile survival according to season of birth was significant, with calves born during the dry season experiencing the highest survival probability. Phenological match may confer a juvenile survival advantage to offspring born during the dry season from greater accumulated maternal energy reserves in mothers who conceive in the long rainy season, high-protein browse in the late dry-early short rainy seasons supplementing maternal and calf resources, reduced predation due to decreased stalking cover, or some combination of these. Asynchrony is believed to be the ancestral state of all ungulates, and this investigation has illustrated how seasonal variation in vegetation can affect juvenile survival and may play a role in the evolution of synchronous births.     

Red howler monkey birth data II: Interannual,habitat, and sex comparisons

Data presented in this paper are derived from the births and subsequent histories of red howler infants born in two habitats. Overall the sex ratio of infants at birth was about 1:1. Infant survivorship (at 1 yr) was about 80%, and 44% of infant mortality was attributed to infanticide by males. Survivorship curves indicated a dramatic sex difference, with far fewer females than males known to be alive at age 7 yr. However, this sex difference may be inflated because emigrant males are more easily identified than emigrant females, and females may be dispersing beyond the boundaries of the study area at a higher rate. Annual birthrate varied somewhat from year to year and was positively related to rainfall. Annual birthrate tended to be higher in the habitat with lower density and higher growth rate. Consistent with the trends, in annual birthrate, variation in interbirth interval length (TBR after births of surviving infants was related primarily to habitat differences and annual variation in rainfall. Season of birth and maternal age class had no effect on IBI. Infant sex had mostly nonsignificant effects on IBI. A small sample indicated that IBI's were significantly longer after the births of females who eventually became natal breeders than after the births of females who eventually emigrated. This difference might reflect differential parental (maternal) investment of some sort.     

Partnership status and the human sex ratio at birth

If two-parent care has different consequences for the reproductive success of sons and daughters, then natural selection may favour adjustment of the sex ratio at birth according to circumstances that forecast later family structure. In humans, this partnership-status hypothesis predicts fewer sons among extra-pair conceptions, but the rival 'attractiveness' hypothesis predicts more sons among extra-pair conceptions, and the 'fixed-phenotype' hypothesis predicts a constant probability of having a son, regardless of partnership status. In a sample of 86 436 human births pooled from five US population-based surveys, I found 51.5% male births reported by respondents who were living with a spouse or partner before the child's conception or birth, and 49.9% male births reported by respondents who were not (chi(2)=16.77 d.f.=1 p<0.0001). The effect was not explained by paternal bias against daughters, by parental age, education, income, ethnicity or by year of observation, and was larger when comparisons were made between siblings. To my knowledge, this is the first direct evidence for conditional adjustment of the sex ratio at birth in humans, and could explain the recent decline in the sex ratio at birth in some developed countries.     

Month of birth related to fecundity and childlessness among contemporary women

To determine the associations of fecundity and childlessness with month of conception and to find a causal mechanism for these associations, we reanalyzed some of our previous data according to the predictions of the seasonal optimal ripening oocyte (SOptRO) and seasonal preovulatory over-ripeness ovopathy (SPrOO) hypotheses. Prime and minor SOptRO months as well as high-risk, no-risk, and very high risk SPrOO months were defined on the basis of a priori knowledge of the existence of ovulatory and anovulatory seasons in mammals and of the general birth distribution in Europe. The month of birth was assessed among 899 mothers with three or more children and 388 childless women extracted from a 1% sample of the Austrian population. The women with three or more children were born in excess during the prime and less often during the minor SOptRO months (chi2 = 2.81; p = 0.045; relative risk = 1.16; 95% CI = 1.01-1.33). This is in line with the SOptRO predictions. The childless women were more frequently born during the high-risk SPrOO months compared to the no-risk months but less often during the very high risk months. The linear trend (chi2 = 8.43; p = 0.009) is in line with the SPrOO predictions. We suggest that fecundity and childlessness are dependent on the gradient of oocyte maturation reflected by mother's month of birth, which may modulate future constitution.     

Sex ratio in the offspring of parents with chronic radiation exposure from nuclear testing in Kazakhstan

The former Soviet Union conducted a nuclear test program in the Semipalatinsk region of northeastern Kazakhstan in 1949-1989. The population in the vicinity of the test site was chronically exposed to radiation fallout, especially from above-ground tests during 1949-1956. Male:female sex ratio has been proposed as a measure of reproductive health, with some reports suggesting an alteration in the sex ratio of offspring of parents exposed to radiation. We investigated the impact of radiation exposure and other factors on the sex ratio in the population inhabiting the exposed region. A total of 11,464 singleton births of 3,992 mothers exposed to radiation during 1949-1956 were analyzed. The overall sex ratio was 1.07, similar to the current sex ratio in Kazakhstan (1.06). The sex ratio increased from 1.04 where mothers received <20.0 cSv to 1.12 where mothers received > or =60.0 cSv. However, the linear trend across exposures was not significant (P = 0.42). No consistent association was found between the sex ratio and the time since parental radiation exposure, parental age at exposure, or year of birth. Sex ratio was significantly associated with maternal age, birth order and possibly ethnicity but not with paternal age, parental educational level or season. In conclusion, no significant association was found between radiation exposure level and sex ratio, but some previously suggested demographic factors were positively associated with sex ratio.     

Presence of maternal anti-HBs antibodies does not influence hepatitis B vaccine response in Brazilian neonates

Recently, it was suggested that maternal hepatitis B surface antigen antibodies (anti-HBs) acquired transplacentally could play a negative role in newborn infants' immune response to the hepatitis B vaccine. We compared the hepatitis B virus (HBV) vaccine response in infants born to mothers previously vaccinated against HBV (n = 91) to infants born to mothers who were not previously vaccinated (n = 221). All newborn infants received three intramuscular doses (10 μg) of HBV vaccine (Butang?) at 0,1 and six months. The first dose was administered at the maternity hospital within 12 h of birth. The geometric mean titres of anti-HBs were not different among newborn infants born to mothers who were anti-HBs-negative (492.7 mIU/mL) and anti-HBs-positive (578.7 mIU/mL) (p = 0.38). Eight infants did not respond to the HBV vaccine. Of them, six were born to anti-HBs-negative mothers and two were born to mothers with anti-HBs titres less than 50 mlU/mL. Despite the mother's anti-HBs-positive status, our data show a good immunogenicity of the Brazilian HBV recombinant vaccine in neonates.     

Determinants of the sex ratio at birth: review of recent literature

The fact that more boys are born than girls (104-107 boys for every 100 girls) has been known since 1662. Factors determining the sex ratio at birth rate are of 2 kinds: factors determining the primary sex ratio, i.e., sex ratio at conception, and factors determining the survival of the embryo in utero. Y-bearing and X-bearing sperm may have different motility or different survival time. The age of the ovum at fertilization and the chemical balance of the female genital tract have an effect on sex ratio at conception. High levels of circulating gonadotropins may imply a lower sex ratio at birth as well as a higher rate of dizygotic twinning. Male conception also appears to be higher early and late in the menstrual cycle. The fact that women exposed to higher coital rates conceive earlier in the menstrual cycle may account for the greater number of boys born during wars. Prenatal male mortality is reportedly highest between gestational months 3-5, lower between months 6-8, and higher again st term. Also, immunological interaction between mother and embryo may account for some sex selective spontaneous abortions. 3 sociodemographic determinants of sex ratio at birth are thought to be maternal age, paternal age, and birth order. Higher prenatal male mortality may be correlated with socioeconomic conditions, since higher socioeconomic status lowers prenatal mortality in general. The effects of parental age, birth order, and parity are less clear. Race is also a factor, since the sex ratio at birth for blacks is lower (102-104) than for whites (106). 14 univariate and 19 multivariate studies of effects of maternal age, paternal age, parity, birth order, race, and socioeconomic status on sex ratio at birth, with sample sizes in the millions from various countries have been analyzed. More boys are born to younger parents, and lower order births have a higher proportion of males than do higher order births. In the multivariate analyses, when the effects of paternal and and birth order are controlled for, the effect of maternal age weakens, and the effect of paternal age appears to be stronger. The effect of birth order remains but is very small, and the effect of race persists independent of any effect of other variables. Maternal age, parity, and birth order are positively correlated with proportion of male stillbirths. The results of the multivariate analyses show all of the effects to be very small, but that maternal age has no effect on sex ratio at birth; paternal age and birth order have a negative effect, and the racial effect persists independent of any other effect. The racial effect is clearly biologically determined at conception because blacks have higher levels of circulating gonadotropin and therefore a higher probability of conceiving girls. Parents in higher socioeconomic classes are more likely to have sons, but the effect is largely due to the excess male mortality during most of the gestational period.     

Acute undernutrition is not associated with excess of females at birth in humans: the Dutch hunger winter

It has been suggested that maternal undernutrition results in adjustment of the sex ratio at birth, favouring females. We tested this hypothesis using births during the Dutch Hunger Winter of 1944-1945, an acute severe famine of seven months' duration. There was no evidence of an excess of female births among deliveries of human infants exposed to famine in any period in gestation. Indeed, among deliveries to women maximally exposed to famine prior to conception, there was an excess (odds ratio = 1.31, 95% CI 1.09-1.58; p = 0.004) of male offspring. Our data do not provide any support for acute and severe maternal undernutrition as a trigger for an increase in female conceptions or in male foetal deaths in human populations.     

Exogenous sex hormone exposure and the risk for VACTERL association

In several studies investigators have suggested that maternal use of exogenous sex hormones during early pregnancy may be associated with various congenital malformations. A group of malformations, the VACTERL (vertebral, anal, cardiac, trachea, esophageal, renal, limb-acronym) association, has been statistically associated with maternal exposure to exogenous sex hormones during the first trimester of pregnancy. The VACTERL association is a nonrandom group of major malformations that occur together more often than would be expected on the basis of chance. To assess this association, we conducted a case-control study of first-trimester exposure to sex hormones among mothers of 34 infants with the VACTERL association and of 1,024 comparison infants with one or more of ten major malformations or Down syndrome. The study subjects were malformed infants born between July 1970 and June 1979 and registered in a population-based birth defects registry. Information concerning the use of exogenous sex hormones during pregnancy was obtained by systematically interviewing the mothers of the malformed infants. Most of the mothers were interviewed within 6 months of their children's births. Each mother was interviewed within a year of her child's birth. We found an odds ratio of 0.98 (90% confidence limits 0.40, 2.38) for the relationship between VACTERL association and use of any sex hormone in the first trimester of pregnancy. Our study had adequate statistical power to detect a true relative risk of 2.8 or greater.     

Absence of effects from immunocontraception on seasonal birth patterns and foal survival among barrier island wild horses

Despite a large body of safety data, concern exists that porcine zonae pellucidae (PZP) immunocontraception--used to manage wild horse populations--may cause out-of-season births with resulting foal mortality. Our study at Assateague, Maryland indicated the effects of immunocontraception on season of birth and foal survival between 1990 and 2002 on wild horses from Assateague Island. Among 91 mares never treated, 69 (75.8%) of foals were born in April, May, and June (in season). Among 77 treated mares, 50 (64.9%) were born in season. Of 29 mares foaling within 1 year after treatment (contraceptive failures), 20 (68.9%) were born in season. Of 48 mares treated for greater than 2 years then withdrawn from treatment, 30 (62.5%) of 48 foals were born in season. There were no significant differences (p <.05) between either treatment group or untreated mares. Survival did not differ significantly among foals born in or out of season or among foals born to treated or untreated mares. Data indicate a lack of effect of PZP contraception on season of birth or foal survival on barrier island habitats.     

Sex ratio at birth and family composition in sub-saharan Africa: inter-couple variations

In this study, sex ratios at birth (male/female births) were found to vary according to family composition. Using Demographic and Health Survey (DHS) maternity histories from sub-Saharan Africa, the study shows that the sex ratio at birth increases with the number of previous male births and decreases with the number of previous female births. For families with only males, the sex ratio increases from 1.046 for the first birth to 1.083 for the 8th birth. For families with only females, the sex ratio decreases from 1.046 for the first birth to 0.942 for the 8th birth. The differences were highly significant when tested with a linear logistic model (p=0.018 for males; p=1.85 x 10(-11) for females). The effect was not symmetrical, and was found to be significantly stronger for females. These effects could be reproduced assuming a strong heterogeneity between couples. The distribution of sex ratios was fitted with an asymmetrical log-gamma function, which revealed a wide range of variation in the sex ratio between 0.50 and 1.30, and a peak around 1.14. The results and their implications are discussed in the light of former findings in France and in the United States of America.     

Adaptive sex ratio variation in pre-industrial human (Homo sapiens) populations?

Sex allocation theory predicts that in a population with a biased operational sex ratio (OSR), parents will increase their fitness by adjusting the sex ratio of their progeny towards the rarer sex, until OSR has reached a level where the overproduction of either sex no longer increases a parent''s probability of having grandchildren. Furthermore, in a monogamous mating system, a biased OSR is expected to lead to lowered mean fecundity among individuals of the more abundant sex. We studied the influence of OSR on the sex ratio of newborns and on the population birth rate using an extensive data set (n = 14,420 births) from pre-industrial (1775-1850) Finland. The overall effect of current OSR on sex ratio at birth was significant, and in the majority of the 21 parishes included in this study, more sons were produced when males were rarer than females. This suggests that humans adjusted the sex ratio of their offspring in response to the local OSR to maximize the reproductive success of their progeny. Birth rate and, presumably, also population growth rate increased when the sex ratio (males:females) among reproductive age classes approached equality. However, the strength of these patterns varied across the parishes, suggesting that factors other than OSR (e.g. socioeconomic or environmental factors may also have influenced the sex ratio at birth and the birth rate.     

A retrospective study of infant mortality of cotton-top tamarins (Saguinus oedipus) in captive breeding

Fifty of 156 (32%) colony bred cotton-top tamarins were stillborn, and 31 (20%) died within the first week after birth. The stillbirth rate was related to litter size and parity in captivity. A higher percent of single births were stillborn (69%) compared to those of twin births (26%) (p less than 0.005). A higher percent of infants born of the first litter in captivity (42%) were stillborn than those of subsequent litters (23%) (p less than 0.025). Stillbirths were not related to season of birth or sex of infant. Survival of live infants was unrelated to season of birth, sex, litter size, or number of litters.     

Birth weight in an African-American population living under moderate ecologic stress

The African-American population of McNary, Arizona, resides at an altitude of 2200 m. The lengthy winters are typically quite cold; the monthly mean temperature from November to April is 1.8 degrees C. Data from 318 singleton full-term births of African-American babies from 1949 to 1972 show a mean weight of 3095 g (s.d. = 427 g). At birth 1.9% of the babies weighed at least 4 kg; 9.7% weighed less than 2.5 kg. These data suggest that altitude may have influenced birth weight in this sample. Significant patterns in birth weight exist for sex, parity, mother's age, and severity of the winter preceding the year of birth. The birth weight of female babies born following warm winters is significantly lighter than those born during years following cold winters. There are relatively fewer high-birth-weight babies, in comparison to other African-American populations. Birth weight is also significantly lighter than three other African-American samples, even though African-American mothers of McNary had full-term professional care. Birth weight of African-American babies born in McNary is consistent with the overwhelming African ancestry of the African-American population of McNary. Sex differences in birth weight of babies born following cold winters can be ascribed to gender-related hereditary or physiologic factors at the level of the fetus. Maternal inactivity during particularly cold winters may be a contributing factor.