Maternal obesity is associated with a wide range of maternal, neonatal and obstetric complications, and is arguably the leading factor associated with high risk pregnancies in the developed world. In particular, there is a strong relationship between obesity and hypertensive disorders of pregnancy (HDP). The mechanisms underlying this relationship have not been fully elucidated, but our understanding of this relationship has been assisted by examining the long term prognosis of women with HDP. Given the importance of obesity as a risk factor for HDP and other complications, preconception care is a critical element in addressing this major public health issue. A detailed review of the literature relating to these issues is presented in Chapter 1 of this thesis.
The aims of this thesis were to:
1. Describe the prevalence and impact of overweight and obesity in an Australian obstetric cohort.
2. Examine the relationship between HDP and obesity, by examining the changes in body mass index (BMI) over time comparing women who did or did not have HDP in an index pregnancy.
3. Examine the relationship between HDP and obesity - associated disease, by examining the long term risk of diabetes in women with and without HDP.
4. Identify potential barriers to the preconception management of overweight and obesity, by assessing, in early pregnancy, women’s knowledge regarding the risks of overweight and obesity in pregnancy and associated health care behaviors.
The prevalence and impact of overweight and obesity on maternal and neonatal pregnancy outcomes in an Australian obstetric population is presented in Chapter 2 (1). This retrospective cohort study of 14 230 women based on the obstetric database at the Mater Mother’s Hospital in Brisbane found that 4809 (34%) of these women were overweight or obese. Overweight and obese women had an increased risk of HDP, gestational diabetes, prolonged hospital admission and caesarean section. Neonates born to obese women had an increased risk of birth defects and hypoglycaemia. Neonates born to morbidly obese women were at increased risk of intensive care nursery admission, premature delivery prior to 34 weeks gestation and jaundice. This study confirmed that overweight and obesity are common in the Australian obstetric context, and that this has important implications for the delivery of obstetric care in Australia.
Next, the long term association between HDP and obesity was examined. This work is presented in Chapter 3 (2). Although obesity is an important risk factor for HDP, most cases of HDP occur in women of normal weight. It was hypothesized that women who developed HDP might have a propensity to gain weight, despite being of normal weight at the time of their affected pregnancy. Change in BMI over time was assessed in a cohort of women with and without HDP. Data was obtained from 3,572 women who received antenatal care at the Mater Mother’s Hospital in Brisbane and who were followed for 21 years, as part of the prospective longitudinal Mater University of Queensland Study of Pregnancy (MUSP). This study showed that HDP are associated with increased weight gain over 21 years and raised the question of whether insulin resistance is a key mechanism underpinning the relationship between obesity and HDP.
Given the potential role of insulin resistance in the relationship between obesity and HDP, the longitudinal relationship between HDP and self reported diabetes 21 years postpartum was examined. This study is described in Chapter 4(3). Data was obtained from a cohort of 3639 women who were followed prospectively as part of the MUSP. This study confirmed that HDP are associated with an increased rate of reported diagnosis of diabetes 21 years postpartum.
Based on the work presented in Chapter 2 and the importance of obesity in pathogenesis of HDP, addressing overweight and obesity prior to conception is an important issue. To identify potential barriers in dealing with the problem of overweight and obesity prior to pregnancy, a survey of 412 consecutive unselected women in early pregnancy was conducted. The results of this work are presented in Chapter 5. Several issues were identified. Overweight and obese women tended to rate their BMI in a lower category. In addition, there was poor adherence with routine preconception health recommendations, inadequate uptake of preconception health checks and failed attempts at weight loss. This survey identified that there is potential to improve the advice that overweight and obese women are given regarding weight loss prior to pregnancy.
In conclusion, obesity is a common and important problem for pregnant women and their offspring both in Australia and globally. It is associated with a broad range of serious complications. A clear causal relationship between obesity and HDP has not been definitively established, although longitudinal studies such as those presented in this thesis suggest a strong association between the two conditions and will hopefully assist in broadening our understanding this relationship. Identifying barriers to dealing with overweight and obesity prior to pregnancy is an important first step towards reducing the adverse health impacts of this condition, both for mothers and their babies.
1. Callaway LK, Prins JB, Chang AM, McIntyre HD. The prevalence and impact of overweight and obesity in an Australian obstetric population. Med J Aust 2006;184:56-9.
2. Callaway LK, McIntyre HD, O'Callaghan M, Williams GM, Najman JM, Lawlor DA. The association of hypertensive disorders of pregnancy with weight gain over the subsequent 21 years: findings from a prospective cohort study. Am J Epidemiol 2007;In Press.
3. Callaway LK, Lawlor DA, Williams GM, Najman JM, O'Callaghan M, McIntyre HD. Diabetes in the 21 years following a pregnancy complicated by hypertension: findings from a prospective cohort study. Am J Obstet Gynecol 2007;In Press.