Human Sexual Size Dimorphism in Early Pregnancy

Sexual size dimorphism is thought to contribute to the greater mortality and morbidity of men compared with women. However, the timing of onset of sexual size dimorphism remains uncertain. The authors determined whether human fetuses exhibit sexual size dimorphism in the first trimester of pregnancy...

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Bibliographic Details
Published in:American journal of epidemiology 2007-05, Vol.165 (10), p.1216-1218
Main Authors: Bukowski, Radek, Smith, Gordon C. S., Malone, Fergal D., Ball, Robert H., Nyberg, David A., Comstock, Christine H., Hankins, Gary D. V., Berkowitz, Richard L., Gross, Susan J., Dugoff, Lorraine, Craigo, Sabrina D., Timor-Tritsch, Ilan E., Carr, Stephen R., Wolfe, Honor M., D'Alton, Mary E.
Format: Article
Language:English
Subjects:
Analysis. Health state
Biological and medical sciences
Birth Weight
Body Size
cohort studies
Epidemiology
Female
fetal development
Fetus - anatomy & histology
Gender differences
General aspects
Humans
Male
Measurement techniques
Medical sciences
Miscellaneous
Mortality
Pregnancy
Pregnancy Trimester, First
Prenatal development
Prospective Studies
Public health. Hygiene
Public health. Hygiene-occupational medicine
Sex Characteristics
Size
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Summary:Sexual size dimorphism is thought to contribute to the greater mortality and morbidity of men compared with women. However, the timing of onset of sexual size dimorphism remains uncertain. The authors determined whether human fetuses exhibit sexual size dimorphism in the first trimester of pregnancy. Using a prospective cohort study, conducted in 1999–2002 in the United States, they identified 27,655 women who conceived spontaneously and 1,008 whose conception was assisted by in vitro fertilization or intrauterine insemination and for whom a first-trimester measurement of fetal crown-rump length was available. First-trimester size was expressed as the difference between the observed and expected size of the fetus, expressed as equivalence to days of gestational age. The authors evaluated the association between fetal sex, first-trimester size, and birth weight. Eight to 12 weeks after conception, males were larger than females (mean difference: assisted conception = 0.4 days, 95% confidence interval (CI): 0.1, 0.7, p = 0.008; spontaneous conception = 0.3 days, 95% CI: 0.2, 0.4, p < 0.00001). The size discrepancy remained significant at birth (mean birth weight difference: assisted conception = 90 g, 95% CI: 22, 159, p = 0.009; spontaneous conception = 120 g, 95% CI: 107, 132, p < 0.00001). These data demonstrate that human fetuses exhibit sexual size dimorphism in the first trimester of pregnancy.
ISSN:0002-9262
1476-6256
DOI:10.1093/aje/kwm024