Introduction
The World Health Organization defines obesity as a body mass index (BMI) of 30 kg/m2 or more (1). Worldwide, over one third of women of reproductive age are now obese (2). In the United States, the reported prevalence of obesity in women of reproductive age between 1999-2002 was 29% (3). More than a decade later this prevalence had risen to 38% (4). United Kingdom, has a reported prevalence of obesity in in women of reproductive age of 10.9% (5), Australia of 28% (6) and Asia of 22% (7).
At the same time, the reported prevalence of gestational diabetes mellitus (GDM) in Europe varies considerably, and in certain populations is reported to occur in more than 20% of pregnancies (8-10) raising to as high as 52% in women with a BMI ≥ 29kg/m2  (11).
With such high and rising prevalence, obesity and GDM have become the most common clinical risks in obstetric practice increasing the probability of a variety of pregnancy-related complications compared to women with a normal BMI and normal glucose tolerance(5, 12-16).
Beyond the impact of a high baseline BMI on pregnancy outcomes, the amount of weight gained during pregnancy can affect the immediate and future health of a woman and her infant. The Institute of Medicine (IOM) guidelines for weight gain in pregnancy recommend weight gain of 5-9kg for all obese women (17). Suboptimal gestational weight gain (GWG), either excessive or inadequate, is also associated with reported maternal and neonatal complications (18-20). Current research indicates that excessive GWG and high pre-pregnancy BMI are associated with increased risks for adverse pregnancy outcomes (19, 21).
Thus, the question remains whether more stringent recommendations for weight gain may improve GDM related outcomes, by reducing the additive effect of diabetes, obesity and excessive weight gain.
Recent studies have shown that in GDM women, minimal GWG led to higher rates of small for gestational age infants (SGA)(18). However, a study of overweight and obese GDM Asian women reported that minimal GWG and tight blood glucose control during pregnancy may eliminate most of the adverse pregnancy outcomes experienced (22).
The primary aim of this study was to investigate the effects of GWG below the IOM recommendation on pregnancy outcomes in women with GDM and a BMI ≥30 kg/m2.
As a secondary aim, we compared pregnancy outcomes in obese GDM women with insufficient GWG, the IOM recommended GWG and excessive GWG.