Pregnancy among women who over-reported condom use as measured by a biomarker for unprotected sex

Adolescents may use condoms inconsistently or incorrectly. This study uses a biomarker for semen Y-chromosome (Yc) detected on a vaginal swab to evaluate the accuracy of adolescent women's reports of condom use. 715 low socioeconomic status African-American adolescent women recruited from central urban Atlanta STD clinics were surveyed at baseline, 6 months, and 12 months. 30.3% of the women who reported perfect condom use tested positive for Yc at baseline, as did 20.2% at 6 months. Women who tested positive for Yc at baseline were about 4.5 times as likely to become pregnant in the next 6 months than women who did not, in logistic regression adjusting for condom and oral contraceptive use (p=0.005). Similarly, women who tested positive for Yc at 6 months were 2.4 times as likely to become pregnant (p=0.11). The Yc biomarker can tell women whether they are using condoms correctly and consistently before unwanted pregnancy. The Yc biomarker may also be a useful measure for survey researchers seeking to validate survey questions about condom use and unprotected sex in different populations.