Childhood adiposity and women's reproductive health

Background: The recent global epidemic of childhood overweight and obesity has significant clinical and public health implications, including for reproductive health. Adiposity (fatness) in childhood is associated with earlier onset of puberty, menstrual irregularity and polycystic ovary syndrome (PCOS) symptoms in adolescent girls. Adiposity in adult women is associated with greater risks of reproductive disorders, for example higher rates of infertility, menstrual disorders, pregnancy complications and menopausal symptoms. As the interest in the longterm health impacts of childhood adiposity grows, there is a need to better understand how childhood adiposity associates with female reproductive health in adulthood. Aims: This thesis aimed to investigate the associations of different measures of childhood adiposity with reproductive outcomes in women including infertility, pregnancy hypertension, menstrual irregularity, PCOS and menopausal symptoms. Methods: Data from two population-based cohorts were used for the analyses. The Childhood Determinants of Adult Health (CDAH) study from Australia was used to investigate associations of childhood adiposity with infertility, pregnancy hypertension, menstrual irregularity, PCOS and menopausal symptoms. CDAH is a follow-up study of 8,498 children with 4,191 girls aged 7-15 years who participated in 1985 Australian Schools Health and Fitness Survey (ASHFS), with up to 1,894 women included in the analyses. The Babies substudy of the Bogalusa Heart Study (BBS) from the United States of America (USA) was also used to investigate associations of childhood adiposity with menstrual irregularity and PCOS. The Bogalusa Heart Study (BHS) has followed-up a biracial population sample (65% white and 35% white) initially recruited at ages 3-18 years in 1973 in Bogalusa, Louisiana. The BBS sub-study of the BHS began in 2013 with a follow-up of 1,803 female participants. The main childhood adiposity measures described in this thesis were body mass index (BMI) and waist-to-height ratio (WHtR). Childhood overweight and obesity were defined by international age-sex-specific standards for BMI. Childhood abdominal obesity was defined as WHtR ‚Äöv¢‚Ä¢0.5. Reproductive outcomes of infertility, pregnancy hypertension, menstrual irregularity, PCOS and menopausal symptoms, including vasomotor symptoms, vaginal dryness, total symptoms and three domain-specific symptoms (somatic, psychological and urogenital), were self-reported. Results: Childhood obesity before 12 years of age, as defined by BMI, appeared to increase the risk of female infertility. Childhood adiposity was associated with increased risk of pregnancy hypertension, with the association of childhood abdominal obesity independent of adult abdominal obesity. Childhood adiposity was not associated with vasomotor symptoms and vaginal dryness that are consistently associated with menopause, but it was associated with more severe total, somatic, psychological and urogenital menopausal symptoms that are not clearly attributable to menopause in women aged 45-49 years. In both CDAH and the BBS cohorts, childhood adiposity was associated with an increased risk of menstrual irregularity and PCOS. However, the association with PCOS was present only in white and not black participants. The risks of adverse reproductive outcomes tended to be highest in women with persistently high adiposity from childhood to adulthood. Conclusions: Childhood adiposity has important implications for the risks of adverse reproductive health outcomes in adulthood including infertility, pregnancy hypertension, menstrual irregularity, PCOS, total and three domain-specific menopausal symptoms, but not vasomotor symptoms and vaginal dryness in women aged 45-49 years. The prevention of childhood adiposity is important for reproductive health as well as disease prevention. Furthermore, as cumulative exposure to high adiposity status across the life course was associated with significantly higher risks of these adverse reproductive health outcomes, early intervention and prevention of high adiposity trajectories may help improve future women's reproductive health.