Heliogeophysical correlates of early biodemographic variables in the south of western Siberia

In order to verify associations between solar and geomagnetic activities and perinatal variables the monthly distributions of population characters in Novosibirsk region over the period 1980-2001 were compared by stepwise correlation analysis with monthly averaged physical parameters at lags from 0 to 10 months. Three indices used were as follows: the number of sunspots, solar flux at 10.7 cm wavelength and Ak index measured at local ionospheric station near Novosibirsk city. Official data on the number of single and multiple live births, stillbirths and infant deaths at the age under one year by the type of population and sex were provided by State Statistical Committee. All three physical parameters positively correlated with the number of single births and infant mortality rate and negatively with twin births in both populations, urban and rural, irrespective of lags. The direct association between Ak index and relative number of stillbirths in urban setting was mostly pronounced at a lag of 5 months. The number of live births increased along with Ak index due to the enhanced proportion of female births whereas the number of stillbirths after the increase in solar and geomagnetic activities elevated because of male deaths.     

Reproductive life of some Gujar women of Punjab

Data was collected on current age, age at menarche, marriage age, maternal age at 1st birth, age at the birth of last child, age at menopause, total number of conceptions, live births, stillbirths, abortions, dead children and living children for a sample of 150 Gunjar women of Punjab, India, during September and October 1977 to study their reproductive life. The women ranged in age from 45-55 years. The mean age at menarche was 14.90 years for the sample. The median age at menopause was 46.20 years. The mean age at marriage of the present sample was 12.56+-2.50 years; the mean age of the mother at the birth of her 1st child was 16.85 years; and the mean age at the birth of the last child was 38.68 years. The average number of conceptions was 7.2; the average number of live births of these 150 women was 6.90. The fertility of this population was natural as they were not using any family planning method.     

An epidemiologic study of congenital malformations of the anterior abdominal wall in more than half a million consecutive live births.

The records of an ongoing health surveillance registry that utilizes multiple sources of ascertainment were used to study the incidence rate of congenital malformations of the anterior abdominal wall in live-born children in British Columbia during the period 1964--1978 inclusive. No overall increase in incidence rate of these anomalies was detected during the study period. The estimated live-born incidence rates were: one in 4,175 live births for omphalocoele, one in 12,328 live births for gastroschisis, and one in 29,231 live births for prune belly. The data were analyzed with regard to sex and associated anomalies. Some practical implications regarding assessment of these infants are discussed.     

Is there a familial link between Down's syndrome and neural tube defects? Population and familial survey

Objective To verify whether Down''s syndrome and neural tube defects arise more often in the same family than expected by chance.Design Population and familial survey.Setting Network of maternity hospitals in the Latin American collaborative study of congenital malformations (ECLAMC) in Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Paraguay, Peru, Uruguay, and Venezuela between 1982 and 2000.Probands 2421 cases of neural tube defects, 952 of hydrocephalus, and 3095 of Down''s syndrome registered from a total of 1 583 838 live births and stillbirths.Main outcome measures Observed number of cases of Down''s syndrome among siblings of probands with a neural tube defect or hydrocephalus and number expected on the basis of maternal age; observed number of cases of neural tube defects or hydrocephalus among siblings of probands with Down''s syndrome and number expected according to the prevalence in the same population.Results Five cases of Down''s syndrome occurred among 5404 pregnancies previous to a case of neural tube defect or hydrocephalus, compared with 5.13 expected after adjustment by maternal age. Twelve cases of neural tube defect or hydrocephalus occurred among 8066 pregnancies previous to a case of Down''s syndrome, compared with 17.18 expected on the basis of the birth prevalence for neural tube defects plus hydrocephalus in the same population.Conclusion No association occurred between families at risk of neural tube defects and those at risk of Down''s syndrome.     

Temporal trends in the secondary sex ratio in Nordic countries

Attempts have been made to identify factors influencing the number of males per 100 females at birth, also called the secondary sex ratio. It has been proposed to vary inversely with the frequency of prenatal losses, but available data lend at best only weak support for this hypothesis. Statistical analyses have shown that comparisons between secondary sex ratios demand large data sets. Variations in the secondary sex ratio that have been reliably identified in family data have mostly been slight and without a notable influence on national birth registers. For Sweden, 1751-1950, the secondary sex ratio among all births and live births revealed increasing trends. The Swedish results are compared with available findings for live births in Finland, Norway, Denmark, and the small Icelandic population. For Norway and Denmark, the secondary sex ratio increased during 1801-1950. A similar, but stronger pattern was observed for Finland (1751-1950) and Iceland (1838-1950). During the latter half of the twentieth century, marked decreases were observed in all countries. Attempts to identify reliable associations between secondary sex ratios and stillbirth rates have been made, but no consistent results have emerged.     

Spina bifida and hydrocephalus: a population study over a 35-year period.

The records of the B.C. Health Surveillance Registry were used to analyze all live births with spina bifida and hydrocephalus (SBHC) in British Columbia between 1952 and 1986 inclusive. A total of 479 cases (218 males and 261 females) occurred during this period in 1,298,267 consecutive live births, for an incidence of 3.7/10,000. There were more females, with the sex ratio being significantly different from that of the general population born over this period. No significant seasonal differences were observed over the time period. A comparison of life expectancy for individuals born 1962-1970 and 1970-1986 showed significant improvement in the probability of surviving to the age of 1 year for the latter group. There was also a small but statistically significant increased chance of surviving to age 7 years in the latter group but no difference in the probability of surviving from 7 years to 16 years. Life expectancy figures are shown in a format practical for counseling with regard to prognosis for affected individuals. Additional malformations not attributable to SBHC were observed in 6% (27 cases). These included renal anomalies, cleft lip and/or palate, tracheoesophageal fistula, and diaphragmatic hernia. The incidence of each defect was significantly greater than in the general population of births.     

Unwanted conceptions: Research on undesirable consequences

Attempts have been made to identify factors influencing the number of males per 100 females at birth, also called the secondary sex ratio. It has been proposed to vary inversely with the frequency of prenatal losses, but available data lend at best only weak support for this hypothesis. Statistical analyses have shown that comparisons between secondary sex ratios demand large data sets. Variations in the secondary sex ratio that have been reliably identified in family data have mostly been slight and without a notable influence on national birth registers. For Sweden, 1751–1950, the secondary sex ratio among all births and live births revealed increasing trends. The Swedish results are compared with available findings for live births in Finland, Norway, Denmark, and the small Icelandic population. For Norway and Denmark, the secondary sex ratio increased during 1801–1950. A similar, but stronger pattern was observed for Finland (1751–1950) and Iceland (1838–1950). During the latter half of the twentieth century, marked decreases were observed in all countries. Attempts to identify reliable associations between secondary sex ratios and stillbirth rates have been made, but no consistent results have emerged.     

Heliogeophysical correlates of early biodemographic variables in the South of Western Siberia

In order to verify associations between solar and geomagnetic activities and perinatal variables, the monthly distributions of population characters in Novosibirsk Region over the period 1980–2001 were compared by stepwise correlation analysis with monthly averaged physical parameters at lags from 0 to 10 months. The three indices were: number of sunspots, solar flux at 10.7 cm wavelength, and A _k index measured at a local ionospheric station near the city of Novosibirsk. Official data on the numbers of single and multiple live births, stillbirths and infant deaths at the age under one year indicating the type of population and gender were provided by the State Statistical Committee. All three physical parameters positively correlated with the number of single births and infant mortality rate and negatively with twin births in urban and in rural populations, irrespective of lags. The direct association between A _k and the relative number of stillbirths in urban setting was mostly pronounced at a lag of 5 months. The number of live births increased along with A _k owing to the enhanced proportion of girls born, whereas the number of stillbirths after the rise in solar and geomagnetic activities increased because of boy deaths.     

Demographic and socioeconomic determinants of low birth weight and preterm births among natives and immigrants in Greece: an analysis using nationwide vital registration micro-data

The present study makes use of nationwide individual-level vital registration data on the single live births occurring in Greece in 2006 to explore associations of socio-demographic factors with adverse pregnancy outcomes, using multinomial logistic regression models. The findings indicate that important risk factors associated with low birth weight preterm and intra-uterine growth retarded births (IUGR) include female sex, primiparity, age of mother over 35, illegitimacy and prior history of stillbirths, infant and child deaths. These constitute risk factors for normal weight preterm births as well, though associations with sex and primiparity in this case point to the opposite direction. Residing in large metropolitan areas is related to a greater risk of an IUGR birth. Among Greek women, educational attainment has a protective effect while housewife status is linked to higher chances of an IUGR birth. For immigrant mothers however, the opposite holds. The study also shows that normal weight preterm births form a distinct group.     

Increasing pre-term and low-birth-weight rates over time and their impact on infant mortality in south-east Brazil

This study investigates the possible effects of pre-term births and low birth weight on infant mortality rates (IMRs) over a 15-year period in Ribeir?o Preto, Brazil, based on surveys carried out in 1978/79 and 1994. The 1978/79 survey included 6750 births over a 12-month period and the 1994 survey 2846 births over a 4-month period. Infant deaths were retrieved monthly from the city register. Infant mortality rate decreased from 36.6 to 16.9 deaths per 1000 over 15 years. The decrease in IMR was larger in the 2500-2999 g group than in any other group. The observed falls in IMR were attributable to decreases in birth-weight-specific mortality rates. Likewise, there was a general decrease in IMR in mild, moderate and severe pre-term births. The incidence rate ratio of infant mortality between surveys was 0.46 (95% CI 0.34-0.63); it increased to 0.57 (95% CI 0.35-0.75) when adjusted for birth weight and other factors in the model and rose to 0.69 (95% CI 0.49-0.97) when adjusted for length of gestation and other variables. The increase in pre-term births and low birth weight may have had, at most, a marginal effect on the IMR. Progress in the care of newborns may have decreased the mortality risk, but even mild pre-term birth still has an impact on infant mortality. There is room for further improvement in IMR by tackling the high rates of pre-term birth.     

A TEN-YEAR STUDY OF ANENCEPHALY

The incidence of anencephaly at the Los Angeles County General Hospital during the period of July, 1948 through June, 1958 was 0.049 per cent. Worldwide the range of reported incidence is 0.012 per cent to 0.671 per cent.In this study 65 per cent of the total number of anencephalics delivered were females, a predominance agreeing with reports by other investigators.Polyhydramnios appeared in 38 per cent of the anencephalic pregnancies of this study, while 15 per cent of the deliveries were complicated by placenta praevia.A significant number (48 per cent) of the multiparae gave a history of previous stillbirths or abortions.The present study does not support observations by other investigators which indicated an increase in anencephalic births during the winter months.Evidence from stillbirth statistics would seem to indicate that anencephaly is primarily a genetically induced phenomenon. Further evaluation and analysis of the predominance of females in anencephalic stillbirths and abortions is suggested, in order to study whether the observed secondary or birth sex ratio (in which males predominate) is, in fact, due to genetic effect.     

Epidemiology of Down syndrome in South Australia, 1960-89.

During 1960-89 687 Down syndrome live births and 46 Down syndrome pregnancy terminations were identified in South Australia. Ascertainment was estimated to be virtually complete. The sex distribution of Down syndrome live births was found to be statistically different from the non-Down syndrome live-birth sex distribution (P less than .01). Smoothed maternal age-specific incidence was derived using both maternal age calculated to the nearest month and a discontinuous-slope regression model. The incidence of Down syndrome at birth for the study period was estimated to be 1.186 Down syndrome births/1,000 live births. Annual population incidence was shown to be correlated with trends in the maternal age distribution of confinements. If current trends in the maternal age distribution of confinements continue, the population incidence of Down syndrome in South Australia is predicted to exceed 1.5 Down syndrome births/1,000 live births during the 1990-94 quinquennium.     

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.     

Estimation of births averted due to breast-feeding and increases in levels of contraception needed to substitute for breast-feeding

After contraceptive use, breast-feeding duration is the major determinant of the birth interval length. Three methods of estimating births averted by breast-feeding, and the increase in contraceptive use needed to substitute for breast-feeding, are presented. Method 1 simply utilizes Bongaarts' Ci, and the other two are based on mean birth intervals with and without breast-feeding. Estimates for each method are derived for six countries with DHS surveys from the mid-1990s: Burkina Faso, Uganda, India, Indonesia, Brazil and Peru. The estimated percentage of additional births that would occur if there were no breast-feeding ranged from 1-4%, in Brazil to about 50% in Burkina Faso and Uganda, reflecting very low breast-feeding in Brazil and very high levels in the sub-Saharan African nations. Strengths and limitations of the three methods are considered.     

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.     

A statistical analysis of the effect of warfare on the human secondary sex ratio

Many factors have been hypothesized to affect the human secondary sex ratio (the annual percentage of males among all live births), among them race, parental ages, and birth order. Some authors have even proposed warfare as a factor influencing live birth sex ratios. The hypothesis that during and shortly after periods of war the human secondary sex ratio is higher has received little statistical treatment. In this paper we evaluate the war hypothesis using 3 statistical methods: linear regression, randomization, and time-series analysis. Live birth data from 10 different countries were included. Although we cannot speak of a general phenomenon, statistical evidence for an association between warfare and live birth sex ratio was found for several countries. Regression and randomization test results were in agreement. Time-series analysis showed that most human sex-ratio time series can be described by a common model. The results obtained using intervention models differed somewhat from results obtained by regression methods.     

Risk factors for perinatal mortality in Canada

A population-based computer record-linkage study of infant births and deaths in 1978 and 1979 in eight Canadian provinces (Quebec and Newfoundland were excluded) was undertaken to permit analysis of perinatal mortality in relation to maternal and infant characteristics. Perinatal mortality rates were significantly higher in nonurban than in urban areas (p < 0.05). A logistic regression model was used to assess the effects on perinatal mortality of variables reported on birth and stillbirth records. This model included length of gestation, infant''s birth weight and sex, number of previous births and number of previous stillbirths as well as an interaction term for length of gestation and birth weight. For early-neonatal mortality, odds ratios over 8 were observed for birth weight less than 2500 g or gestation less than 35 weeks. About 75% of early-neonatal mortality was attributable to low birth weight or fetal immaturity. Greater emphasis should be placed on the prevention of low birth weight.     

Increased Frequency of Aneuploidy in Long-Lived Spermatozoa

Aneuploidy commonly causes spontaneous abortions, stillbirths, and aneuploid births in humans. Notably, the majority of sex chromosome aneuploidies in live births have a paternal origin. An increased frequency of aneuploidy is also associated with male infertility. However, the dynamics and behavior of aneuploid spermatozoa during fertilization in humans have not been studied in detail. Therefore, we compared the frequency of aneuploidy and euploidy in live spermatozoa from normozoospermic men over a 3-day period. To assess the dynamics and behavior of aneuploid spermatozoa, we simultaneously evaluated sperm viability using the hypo-osmotic swelling test and sperm aneuploidy using fluorescence in situ hybridization. Whereas the frequency of viable euploid spermatozoa significantly decreased over 3 days, the frequency of viable spermatozoa with aneuploidy interestingly showed a time-dependent increase. In addition, spermatozoa with abnormal sex chromosomes survived longer. To compared with spermatozoa with other swelling patterns, those with tail-tip swelling patterns had a lower frequency of aneuploidy at all time points. This study revealed the novel finding that the frequency of aneuploid spermatozoa with fertilization capability significantly increased compared to that of euploid spermatozoa over 3 days, suggesting that aneuploid spermatozoa can survive longer than euploid spermatozoa and have a greater chance of fertilizing oocytes.     

Sex ratios at birth in African populations: a review of survey data

This study analyzes the distribution of sex ratio at birth in African populations using data collected in birth histories in sample demographic surveys (Demographic and Health Surveys and World Fertility Surveys). The average sex ratio from 56 surveys, totaling 1.130 million births, was 1.033 (95% CI, 1.029-1.037), significantly different from the world average of 1.055. The distribution of sex ratios across surveys was found to be heterogeneous, and different from what could have been expected from random fluctuations due to sample size. Three subsets were identified: a subset with lower sex ratios, primarily in countries of eastern and southern Africa of Bantu populations (1.010), a subset with average sex ratios (1.035), and a subset of countries with higher sex ratios, in particular Nigeria and Ethiopia (1.070). Further analysis revealed that African populations are as diverse as other populations, with sex ratios ranging from low values (below 1.00) to high values (above 1.08). Results are discussed in light of independent data sources and in comparison with other human populations.