Obesity: the burden of disease
Obesity has been identified by the World Health Organisation as a significant global health problem, contributing to the overall burden of disease worldwide . Obesity is associated with a reduction in life expectancy, through an increased risk of adverse health consequences related to cardiovascular disease, type 2 diabetes and several cancers .
The impact of obesity during pregnancy
Obesity is a significant health issue for women during pregnancy and childbirth, with estimates suggesting that 35% of Australian women aged between 25 and 35 years are overweight or obese . Approximately 34% of pregnant women have a body mass index (BMI) in excess of 25 kg/m2, although recent data indicates this to be increasing further, and approaching 50% [5, 6]. There are well-documented risks associated with obesity during pregnancy. Maternal complications include an increased risk of hypertension and pre-eclampsia,[4–17] gestational diabetes,[4–6, 10, 11, 15, 16] infection and thromboembolic disease [9, 13]. Women who are overweight or obese are more likely to require induction of labour,[5, 6, 10, 13, 14, 16] and have increased risk of caesarean section [4–6, 10–18]. Women who are overweight or obese are more likely to suffer a perinatal death [4, 10, 12, 14, 17–22]. Infants of mothers who are overweight or obese are more likely to be macrosomic,[5, 6, 15, 17, 19–21] require admission to the neonatal intensive care unit,[4, 6, 19–21] be born preterm,[4, 6, 19–21] be identified with a congenital anomaly,[4, 19–21] and to require treatment for jaundice or hypoglycaemia [4, 6, 16].
We have published maternal and infant health outcome data available for all women birthing in South Australia in 2008, involving in excess of 19,600 confinements . Risk ratios (RR) and 95% confidence intervals (CI) for health outcomes for women in various BMI categories were compared with women of healthy BMI (less than 25 kg/m2), demonstrating an increased risk in adverse maternal and infant health outcomes with increasing maternal BMI, consistent with other reported literature [4, 5].
Gestational weight gain recommendations
There is a substantial literature on maternal weight gain in pregnancy that has been summarised by the Institute of Medicine [23, 24]. While most studies have reported average weight gains of 10-15 kg, this varied considerably among overweight and obese women, with many women exceeding this average .
Cedergren and colleagues evaluated the effect of maternal BMI and gestational weight gain in more than 240,000 women in Sweden . While obese women with gestational weight gain less than 8 kg had a reduced risk of large-for-gestational age babies, pre-eclampsia, caesarean section and operative vaginal birth, high gestational weight gain was associated with an increased rate of caesarean section across each of the 5 BMI categories. Cedergren concluded that obese women may benefit from a limited weight gain in pregnancy, as has been recommended by the Institute of Medicine [23, 24].
Conversely, too severe restriction of maternal diet may have implications for fetal growth and development. While Cedergren and colleagues demonstrated a reduction in the risk of large for gestational age infants among women with less than 8 kg weight gain in pregnancy, this appeared to be at the expense of an increase in the proportion of small infants at the opposite end of the birth-weight spectrum . This finding has not been demonstrated in the randomised trial ACHOIS where, for women with gestational diabetes, treatment with dietary and exercise advice designed not to promote weight loss was associated with a significant reduction in the incidence of macrosomia without any increase in the risk of small for gestational age infants.
While restriction of weight gain in pregnancy increases the incidence of spontaneous preterm birth in women with a normal BMI, this has not been demonstrated in overweight or obese women . Thus recommendations have been made to avoid weight loss during pregnancy and to limit restriction of weight gain to approximately 5 kg throughout pregnancy .
Reducing the burden of disease related to Obesity in Pregnancy
While there is an extensive body of literature related to defining the problems and potential complications associated with obesity during pregnancy and childbirth, there is more limited information available related to effective interventions that may be implemented to improve maternal, fetal and infant health outcomes. Current practice guidelines recommend that women should be counselled prior to conception and encouraged to make lifestyle changes .
Systematic Review of the Literature
Our systematic review published in 2008 identified 2 published randomised trials, assessing antenatal interventions for overweight and obese women during pregnancy. Our updated systematic review and meta-analysis published in 2010 included 9 randomised trials, involving 743 women and infants . There were no statistically significant differences identified between women who received an antenatal intervention and those who did not for the outcome large-for-gestational-age infant (three studies; 366 women; risk ratio 2.02; 95% CI 0.84, 4.86) or mean gestational weight gain (four studies; 416 women; weighted mean difference -3.10 kg; 95% CI -8.32, 2.13 (random effects model). There were no statistically significant differences identified for other reported outcomes.
There are limitations of the current evidence on the effect of an antenatal dietary intervention to limit gestational weight gain for women who are overweight or obese, including the lack of reporting of maternal and infant outcomes.
Aims of the trial
The aims of this randomised, controlled trial are to assess whether the implementation of a package of dietary and lifestyle advice to overweight and obese women during pregnancy to limit weight gain is effective in improving maternal, fetal and infant health outcomes.
The primary hypothesis is that the implementation of a package of dietary and lifestyle advice to overweight and obese women during pregnancy to limit gestational weight gain will
The secondary hypotheses are that the implementation of a package of dietary and lifestyle advice to overweight and obese women during pregnancy to limit gestational weight gain will