Decreasing Sex Difference in Birth Weight
Notice bibliographique
Résumé
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
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,003 | 0,024 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,001 | 0,002 |
| Études des sciences et des technologies | 0,000 | 0,001 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,001 | 0,002 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,009 | 0,001 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».