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Philip Lalor, MHealSc, 2012



The objective of this study was to conduct a literature review and a retrospective analysis of a cohort of New Zealand women to determine the relationship between weight and complications in pregnancy. The literature review was undertaken to develop knowledge and understanding of the relationship between the pre-pregnancy weight of a woman and complication and outcomes during the antepartum, intrapartum and postpartum periods. In addition, the review sought to determine complications and outcomes that relate to the neonate in the perinatal period. The review was also means of identifying rates of outcome in other populations, relevant terms, definitions and terminology.
The information gathered in the literature review determined the scope of outcomes and complications to be examined during the quantitative analysis phase of this study. The analysis focused on a large cohort of women who delivered in Canterbury District Health Board (CDHB) facilities to understand and empirically determine the magnitude of association between overweight and obesity and pregnancy complications and adverse outcomes.

Design of Quantitative Study, Setting and Participants

The study design is a retrospective closed cohort study of 6174 eligible women who delivered in CDHB facilities between the 1st of March 2011 and 31 March 2012. Some 4759 women were confirmed eligible, as they had self-reported pre-pregnancy height and weight available for analysis.

Main Outcome Measures

The outcome measures were motivated by the findings of the literature review whereby odds ratio values were calculated in most instances to measure the magnitude of increased odds of outcome of complication or adverse outcome in the antepartum, intrapartum and postpartum periods, and of the neonate, compared to a reference group that were defined by anthropometric measures. The main anthropometric outcome measure for body size was self-reported pre-pregnancy Body Mass Index (BMI), calculated as weight in kilograms divided by height in meters squared. Analyses were stratified according to BMI category and adjusted for potential confounders that related to demographics.


Overall, 2,576 (54.1%) women were classified as underweight or normal, 1,263 (26.5%) as overweight, and 920 (19.3%) as obese. A number of significant associated between body size and pregnancy complications were identified. Compared to women classified as underweight or normal, obese women had significantly increased adjusted odds of an admission to an obstetric unit during the gestational period due to complications (odds ratio (OR): 1.27 [95% CI: 1.07, 1.51]). There are increased odds of a prolonged pregnancy for women who were classified as being overweight (OR: 1.59 [95% CI: 1.22, 2.07]) or obese (OR: 1.51 [95% CI: 1.12, 2.03]) compared to women classified as being underweight or normal.
In the intrapartum period, induction of labour was significantly related to body size classification. Compared to women classified as underweight or normal, overweight (OR: 1.24, [95% CI: 1.04, 1.47]) and obese (OR: 1.40 [95% CI: 1.16, 1.69]) women had higher odds of being induced. In addition there is significantly increased odds of requiring the caesarean delivery to performed as an emergency caesarean delivery; overweight (OR: 1.29 [95% CI: 1.07, 1.56]) and obese (OR: 1.37 [95% CI: 1.12, 1.69]) classifications. Consequently there is an increased likelihood of longer stay in hospital post-delivery, for overweight (OR: 1.28 [95% CI: 1.11, 1.47]) and obese (OR: 1.35, [95% CI: 1.15, 1.58]) compared to underweight or normal weight women.
Crude analysis revealed women with weight above normal limits compared to women of normal weight have increased odds of delivering a baby that is consequently diagnosed with a respiratory or cardiovascular condition; overweight (OR: 1.26 [95% CI: 1.01, 1.67]), obese (OR: 1.32 [95% CI: 1.04, 1.67]). However, after adjusting for age, ethnicity, delivery status and smoking status, the significant difference was lost.


Woman who has a higher than normal BMI index values pre-pregnancy had significantly increased odds of complications relating to a number of outcomes compared to women with normal BMI index values. Significant outcomes included: increased odds of admission during pregnancy, induction of labour, caesarean section, emergency caesarean section, longer hospital stays and risk to the neonate in terms of respiratory or cardiovascular complications. The increased odds of adverse outcomes not only increase the risk burden for the patient and offspring but presents additional challenges for the providers of obstetrics and neonatal care in New Zealand.

Supervisor: Philip Schluter

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