Spontaneous premature birth in twin pregnancy.

Factors associated with spontaneous premature birth were investigated in 459 consecutive twin deliveries at this hospital. Low maternal age, low parity, and zygosity were significantly related to the incidence of this complication. The number of previous abortions, sex combinations and related birth order, and mode of presentation of the first twin were not related to the incidence of spontaneous premature delivery. We conclude that apart from low maternal age and low parity there are no obvious factors that would permit early identification of twin pregnancies at risk from spontaneous premature birth.     

Environmental bias in twin studies

Abstract

This study examines the responses of mothers of twin girls about similarities and differences of their monozygotic (MZ) and dizygotic (DZ) twins. After these measures had been completed and scored, the investigator obtained zygosity diagnoses of the twins made by extensive blood‐group analyses. Of the 61 pairs of twins, 11 were misclassified by their mothers. Despite these mothers’ erroneous beliefs about the zygosity of their twins, they described the twins as having similarities and differences appropriate to their true degree of genetic relatedness.     

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

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

Fitting mixture models to birth weight data: a case study.

Birth weights by gestational age are compared in two birth cohorts from Northern Finland, the first from 1966 and the second from 1985-1986. A curious fact in the data is that mean birth weight before the 39th week was lower in the latter series although the mean birth weight for the total series was higher. Similar findings have been reported in other series. A mixture model with the nonparametric regression function is proposed for studying the hypothesis that the difference was caused by more frequent gross errors in gestational assessment in the earlier cohort. The probability of an error in gestational assessment then greatly depends on the observed gestational age, which makes the mixture model nonstandard. Maximum likelihood solutions to the parameters in the proposed model were computed employing the general expectation-maximization (EM) algorithm. A technique for studying the effect of errors on the intrauterine weight gain curve is proposed and applied to our two birth cohorts. The risk of underestimation of gestational age seems to be larger in the previous series and the differences between the growth curves almost totally vanish when "corrected" by means of the mixture model.     

Chromosome breakage in low birth weight newborns.

The frequency of chromosome aberrations in cells cultured from umbilical cord blood was determined for 50 low birth weight (LBW) and 50 normal birth weight (NBW) euploid newborns matched for sex, race, and maternal age. The metaphase spreads had been prepared in the course of an earlier study of frequency of aneuploidy and results are from 72-h cultures, i.e., presumably, at the second division in vitro. There were no significant differences between the two groups in the frequency of cells with chromosome breakage, chromosome gaps, or hyperdiploid cells. There was, however, a significantly higher frequency of hypodiploid cells in the LBW group. The present findings differ from those of others who have reported an increase in chromosome breakage in premature newborns.     

Hyperphenylalaninemia and birth weight

Hyperphenylalaninemias (HPAs) are due to autosomal recessive inherited deficiency of phenylalanine hydroxylase and include three different biochemical and clinical phenotypes: classic phenylketonuria, mild phenylketonuria and persistent HPA. Recently the relationship between birth weight and HPA has been investigated. We performed an evaluation of birth weight in our 260 HPA patients. Our results do not support the view that birth weight is reduced in HPA patients and we found no correlation between birth weight and severity of the disease. Only a better knowledge of genetic mechanisms involved in HPA can clarify the interaction between HPA and fetal development.     

Inferring contemporary and historical genetic connectivity from juveniles

Measuring population connectivity is a critical task in conservation biology. While genetic markers can provide reliable long‐term historical estimates of population connectivity, scientists are still limited in their ability to determine contemporary patterns of gene flow, the most practical time frame for management. Here, we tackled this issue by developing a new approach that only requires juvenile sampling at a single time period. To demonstrate the usefulness of our method, we used the Speartooth shark (Glyphis glyphis), a critically endangered species of river shark found only in tropical northern Australia and southern Papua New Guinea. Contemporary adult and juvenile shark movements, estimated with the spatial distribution of kin pairs across and within three river systems, was contrasted with historical long‐term connectivity patterns, estimated from mitogenomes and genome‐wide SNP data. We found strong support for river fidelity in juveniles with the within‐cohort relationship analysis. Male breeding movements were highlighted with the cross‐cohort relationship analysis, and female reproductive philopatry to the river systems was revealed by the mitogenomic analysis. We show that accounting for juvenile river fidelity and female philopatry is important in population structure analysis and that targeted sampling in nurseries and juvenile aggregations should be included in the genomic toolbox of threatened species management.     

Organic-solvent water pollution and low birth weight in Michigan.

This pilot study explored the association between a measure of water pollution caused by benzene or chlorinated solvents and the incidence of low birth weights for white residents of Michigan counties. A positive relationship between water pollution by these contaminants and the per cent of low-weight births (less than 2,500 grams, or about 5.5 pounds) resulted despite controls for the incidence of teenaged childbearing, infrequent prenatal care, and mean household income from wages or salaries. Water pollution showed an association with the incidence of low birth weight that was as strong as that between low birth weight and low prenatal care. While correlation cannot prove causation, the finding suggests that impure water may impair fetal growth in Michigan.     

Potential bias in NMR relaxation data introduced by peak intensity analysis and curve fitting methods

We present an evaluation of the accuracy and precision of relaxation rates calculated using a variety of methods, applied to data sets obtained for several very different protein systems. We show that common methods of data evaluation, such as the determination of peak heights and peak volumes, may be subject to bias, giving incorrect values for quantities such as R₁ and R₂. For example, one common method of peak-height determination, using a search routine to obtain the peak-height maximum in successive spectra, may be a source of significant systematic error in the relaxation rate. The alternative use of peak volumes or of a fixed coordinate position for the peak height in successive spectra gives more accurate results, particularly in cases where the signal/noise is low, but these methods have inherent problems of their own. For example, volumes are difficult to quantitate for overlapped peaks. We show that with any method of sampling the peak intensity, the choice of a 2- or 3-parameter equation to fit the exponential relaxation decay curves can dramatically affect both the accuracy and precision of the calculated relaxation rates. In general, a 2-parameter fit of relaxation decay curves is preferable. However, for very low intensity peaks a 3 parameter fit may be more appropriate.     

Estimation of penetrance from twin data.

A simple method for estimating the gene frequency p and the penetrance value K from data on polymorphic monogenic characteristics on monozygotic twin pairs is presented. In spite of the method here presented having limited value because the results it yields cannot be evaluated on their own, the estimates of p and K it provides can be indirectly tested by comparing them to the ones obtained in familial aggregates through classical segregation analysis or by using the latter to calculate the expected proportions of dominant-dominant, dominant-recessive and recessive-recessive monozygotic twin pairs. When the method is applied to data on tongue-rolling ability published in the literature, a good agreement is observed between twin and familial estimates, thus indicating that the method is reliable and that it can be used as an ancillary way of corroborating or otherwise evidence of monogenic autosomal dominant mechanism inferred from the analysis of familial data.