Decreasing Sex Difference in Birth Weight
Bibliographic record
Abstract
To the Editor: Among manufactured chemicals, antiandrogenic endocrine disrupters may be especially toxic during fetal life. Indeed, a temporal increase in the prevalence of male genital malformations, including hypospadias and undescended testis, has been observed in recent population-based studies; and geographical differences suggest the role of environmental exposure to antiandrogenic endocrine disrupters.1 Birth weight has consistently been shown to be higher in boys than in girls.2 This is apparently due to androgen action: the birth weight of 46 XY individuals with complete androgen insensitivity is similar to that of girls.3 We hypothesized that if environmental toxicants have disrupted androgen action in male fetuses, the difference between the weight of male and female neonates should have decreased over time. We used graphical methods to examine temporal trends in mean birth weight of all singleton live births from Statistics Canada's database for the years 1981-2003 (N = 5,086,550).4 Because of a strong temporal increase in preterm birth and decrease in postterm birth (both of which would tend to reduce overall mean birth weight), the primary analysis was restricted to term births (37-41 completed weeks). To provide a control comparison, we analyzed the corresponding temporal trends in differences in birth weight between infants of multiparous and primiparous women.2 We also carried out multiple linear regression analyses with birth weight as the dependent variable; gestational age, gestational age squared, maternal age (<20, 20-34, ≥35 years), fetal sex, parity (multiparous vs. primiparous), and year were the independent variables, along with sex-by-year and parity-by-year interaction terms. A negative sex-by-year interaction indicates that the male-female difference has decreased over the study period. All statistical analyses were carried out using SAS version 8.2 (SAS Institute, Cary, NC). Between 1981 and 2003, mean birth weight for boys increased from 3391 to 3507 g; the corresponding figures for girls were 3248 and 3375 g. Similarly, mean birth weight in infants of multiparous mothers increased from 3368 to 3494 g, whereas the mean for infants of primiparous mothers increased from 3261 to 3375 g. The Figure demonstrates a steady temporal decrease in the male-female difference contrasting with a slight increase in the multiparous-primiparous difference. The multiple linear regression analysis confirmed the graphical results (interaction between sex and year −0.57 g/yr [95% confidence interval = −0.69 to −0.44] and between parity and year +0.17 g/yr [+0.05 to 0.30]).FIGURE.: Temporal trends in the differences in mean birth weight (in grams) between male and female and between infants born to multiparous and primiparous mothers (live singleton term [37-41 weeks of gestation] births from 1981 to 2003 in Canada).Recent temporal trends in birth weight seem to differ by infant sex. Control for gestational age and for maternal age and parity in the multiple regression analysis helps ensure that temporal changes in those variables do not confound the declining sex difference in birth weight. Comparisons of temporal trends in the sex difference in birth weight between jurisdictions with variable exposure to endocrine disrupters may help to uncover the biologic mechanisms underlying our findings. Guy Van Vliet Department of Pediatrics University of Montreal, Montreal Quebec, Canada [email protected] Shiliang Liu Health Surveillance and Epidemiology Division Centre for Health Promotion Public Health Agency of Canada Ottawa, Ontario, Canada Michael S. Kramer Departments of Pediatrics and of Epidemiology and Biostatistics McGill University Montreal, Quebec, Canada for the Fetal, and Infant Health Study Group of the Canadian Perinatal Surveillance System
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.002 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".