title: Age at first sexual intercourse and teenage pregnancy in Australian female twins.
abstract: Girls who report first sexual intercourse during their early teen years have much higher rates of teenage pregnancy and childbearing than girls who delay sexual onset until older adolescence. In this study, we examine genetic and environmental influences on variation in teenage pregnancy and covariation with age at first sexual intercourse in two cohorts of Australian female twins. In the older twin cohort, born 1893-1964, we observe substantial heritable variation in teenage pregnancy that is largely shared with heritable variation in age at first sexual intercourse, with shared environment contributing little to variation in teenage pregnancy. Genetic influences on teenage pregnancy are smaller and nonsignificant in the younger twin cohort, born 1964-1971, where shared environment contributes much more and overlaps entirely with shared environmental variation in age at first intercourse.
authors.affiliation: Department of Psychiatry, Washington University School of Medicine, St Louis, Missouri 63110, United States of America. waldronm@psychiatry.wustl.edu
authors.forename: Mary
authors.initials: M
authors.lastname: Waldron
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Heath
authors.forename: Eric
authors.initials: E
authors.lastname: Turkheimer
authors.forename: Robert
authors.initials: R
authors.lastname: Emery
authors.forename: Kathleen K
authors.initials: KK
authors.lastname: Bucholz
authors.forename: Pamela A F
authors.initials: PA
authors.lastname: Madden
authors.forename: Nicholas G
authors.initials: NG
authors.lastname: Martin
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001315:Australia; D015331:Cohort Studies; D003075:Coitus; D004777:Environment; D005260:Female; D006801:Humans; D008875:Middle Aged; D015233:Models, Statistical; D011247:Pregnancy; D011253:Pregnancy in Adolescence / Q000235:genetics* / Q000523:psychology / Q000706:statistics & numerical data*; D014429:Twins, Dizygotic / Q000235:genetics / Q000523:psychology; D014430:Twins, Monozygotic / Q000235:genetics / Q000523:psychology