The association of pregnancy history with areal and volumetric bone mineral density in adolescence

Abstract

Studies demonstrate that pregnancy may interfere with bone mineral density. Adolescence is a crucial time of life for bone mass acquisition and there are some questions as to the influence of pregnancy on bone mass at this age. To evaluate the association between pregnancy history and areal (BMD) and volumetric (vBMD) bone mineral density in adolescence. A cross-sectional study of 119 adolescents ranging from 12-20 years of age was conducted; 30 of these girls had a history of full-term pregnancy. The adolescents were selected during a routine visit to the Adolescent Gynecology Outpatient Facility, completed a questionnaire, and had a physical examination to evaluate weight, height and Tanner stage. Bone mineral densitometry of the lumbar spine (L(1)-L(4)) and total body (TB) was performed to measure bone mineral density and body composition. The mean measurements of the area, bone mineral content (BMC), BMD and vBMD of L(1)-L(4) and the area, BMC and BMD of TB were not significantly different between adolescents with and without a pregnancy history, stratified by chronologic and gynecologic age. The percentage of adolescents with altered Z-scores was similar in both groups, and the prevalence ratio showed no association between pregnancy history and low bone mass (PR=0.52; CI 0.04-6.07). Upon multiple regression analysis, body mass index (BMI) and lean body mass (LBM) were the main factors associated with lumbar spine and total body measurements. Pregnancy history was inversely associated with areal BMD of L(1)-L(4) (R (2)=0.04) and vBMD of L(1)-L(4) (R (2)=0.04), accounting for only 4% variation in the lumbar spine. These data suggest that adolescent pregnancy seems to exert no significant influence on the acquisition of bone mass and does not appear to represent a risk factor for osteoporosis in the future.