Prevalence and predictors of early gestational weight gain associated with obesity risk in a diverse Australian antenatal population: a cross-sectional study

Excessive gestational weight gain (GWG) is an independent risk factor for a myriad of short and long-term complications for both the mother and her offspring [1‐3]. In 2009, the United States Institute of Medicine (IOM) published updated guidelines to provide direction to health professionals around healthy GWG expectations [4]. These guidelines are pre-pregnancy body mass index (BMI) specific and are used to guide clinicians when counselling women regarding weight gain in pregnancy.

While research has focused on overall GWG, trimester specific gains are of growing interest with respect to adverse outcomes. In the short term, excess GWG in the first half of pregnancy irrespective of pre-pregnancy BMI has been shown to increase the risk of gestational diabetes, hypertensive diseases of pregnancy and macrosomia [5‐8]. Longer term consequences include greater postpartum weight retention, increased waist circumference and systolic blood pressure in women up to 7 years postpartum [9, 10]. Excess early pregnancy weight gain, in particular, has been shown to be an independent risk factor for development of gestational diabetes and maternal hyperglycaemia [6, 11, 12]. This may be due to the increase in maternal fat mass during early pregnancy which can increase insulin resistance and thus increase the risk of impaired glucose intolerance [11]. Furthermore, while there should be minimal gain physiologically in the first trimester, excess first trimester weight gain has also been shown to increase the risk of overweight and obesity in offspring in the first 4 years of life [13, 14].

A lack of awareness regarding the risk of excess GWG on health outcomes for the mother and her offspring may be an important factor for excessive GWG [15]. Pregnant woman who are already overweight or obese are less likely to be educated about weight gain recommendations than normal weight women, and have been shown to receive information conflicting with the IOM recommendations [16].

The primary aim of this study was to examine the prevalence and specific health and socio-economic factors which may predict excess early GWG in a diverse early pregnant population. Secondly, we sought to examine the participants understanding of their GWG expectations specific to their BMI and, the significance of GWG on the health outcomes for their baby.

A total of 2313 women completed the questionnaire, of these 2021 were included in this study. Those excluded (n = 292, 12.6%) had missing anthropometry data necessary to enable analysis of GWG or BMI. There were 14 refusals at RPA and Canterbury Hospitals (0.6%), 40 (15.7%) refusals at Campbelltown and 12 (0.3%) from Fairfield. The mean gestational age at recruitment was 19.4 weeks. Maternal socio-demographic characteristics and related variables are shown in Table 2. Underweight women comprised 6.4% (n = 129), normal weight 60.7% (n = 1227), overweight 21.1% (n = 427) and 11.8% (n = 238) obese.

This is the largest Australian survey examining health and sociodemographic factors associated with early GWG and women’s understanding of the importance of healthy GWG in pregnancy. We found that in the first half of their pregnancy, more than one third of the cohort (32.4%) gained gestational weight outside the IOM recommendations for their BMI category and the overweight and obese women were more likely to overestimate the appropriate GWG for their baseline BMI. The most significant predictors of excess early GWG were pre-pregnancy BMI and SES status. It is of concern that only half the cohort (51.0%) understood the potential impact of excess GWG on their baby and furthermore, the women who gained the most weight outside the IOM guideline were less likely to believe that excess GWG would impact negatively on their baby. These findings make it clear that education around GWG is required to advise women about what are the expected healthy GWG parameters for their BMI.

Our findings support other studies that have reported women who are overweight and obese women are more likely to gain excess weight as per the IOM guidelines for their BMI category [2, 18, 19]. Recommendations regarding appropriate GWG are particularly relevant to overweight and obese women who are already at risk of complications for their pregnancy and offspring due to their pre-pregnancy weight. Any additional risks that accompany excessive GWG may further complicate their pregnancy, their future health and the health of their child. There are limited data on how many women are gaining excessive weight in early pregnancy in Australia. Only one Australian study (n = 664) has examined early gestational weight gain, in the context of overall weight gain in pregnancy. This study reported that by 16 weeks of pregnancy, 8% of women had already reached their recommended weight for the total pregnancy, and 2% had exceeded their total weight gain recommended for the pregnancy. [20] The authors also noted that total gestational weight gain correlated with weight gain in early pregnancy. The LIMIT trial found that delivery of advice about diet, exercise and behavioural changes, to women who are already overweight or obese during pregnancy did not reduce the primary outcome (large for gestational age), nor did it influence GWG despite recruiting between 10 and 20 weeks gestation (intervention 9.39 ± 5.74 kg; standard care 9.44 ± 5.77 kg; p = 0.89) [21].

Even though pre-pregnancy BMI is a significant predictor of early excess GWG in our study, up to a third of normal weight women also gained weight in excess of that recommended by the IOM. This is of concern because even women with a healthy weight are at risk, because early excess GWG significantly increases the risk of gestational diabetes, particularly amongst normal weight women [6, 22].

We found women from lower SES backgrounds were more likely to gain weight in early pregnancy in excess of the IOM recommendations. This finding aligns with previous studies which have consistently shown an association between lower SES background and excess GWG [23, 24]. Women who are socio-economically disadvantaged are likely to have greater psychosocial risks such as stress, depression, poor social supports and unplanned pregnancy, which may contribute to poor dietary choices and minimal physical activity [25]. Furthermore, women from higher SES areas tend to be more proactive with seeking information regarding weight gain recommendations, healthy eating and exercise during pregnancy [25].

Our cohort of overweight and obese women was more likely to overestimate their appropriate GWG suggesting that there is a lack of knowledge regarding healthy GWG by women, especially those most at risk – the overweight and the obese. Our findings validate findings from a smaller Australian study (n = 364) that examined pregnant women’s knowledge of GWG expectations and their awareness of complications associated with obesity and excess GWG [26]. A second small Australian study recruited pregnant women at 16–18 weeks gestations (n = 166), comparing GWG expectations over reported GWG. A significant risk factor for excess GWG was mothers overestimating the minimum amount of GWG needed [15]. Our study differed from these; it was confined to early pregnancy, had a much larger sample size and included women from diverse ethnic and cultural backgrounds.

We have demonstrated the paucity of knowledge by pregnant women regarding the importance of optimal GWG. Preconception care has been shown to be effective with reducing the amount of gain pregnant women gain up until their first booking visit at hospital [27, 28]. Our results call for counselling and discussion regarding both expectations about optimal GWG and consequences of excess GWG. The Cochrane Review of directed preconception health programs and interventions for improving pregnancy outcomes for women who are overweight or obese was unable to include any studies for meta-analysis [29]. These conversations should be initiated preconception or at the very least in early pregnancy with their healthcare practitioner. Despite this being good practice, international studies suggest that few women receive such advice [30‐32]. Research exploring reasons for this lack of counselling from healthcare professionals [30, 31] has found the reasons to be limited awareness of current pregnancy weight gain guidelines, belief that such counselling is ineffective, or awkwardness about raising the issue of weight and weight gain with women. If healthcare providers do counsel women and outline expected GWG recommendations, encouragingly there is an increased likelihood of appropriate GWG, particularly when additionally offered lifestyle coaching [33]. The timing of an intervention or patient education is however important. Our study shows women are already gaining excessive weight in early pregnancy and remain at risk of adverse outcomes independent of total GWG and pre-pregnancy BMI.

Our finding that Middle Eastern and Pacific Islander/Maori women were more likely to have excess GWG compared with other ethnic backgrounds was not sustained in the multivariate analysis but warrants further investigation as the evidence is inconclusive around ethnicity as a risk factor for excess GWG [34‐38]. Research from New Zealand in the early pregnancy period has reported that Pacific Islander and Maori women women’s knowledge of their BMI and recommended GWG to be inaccurate, irrespective of BMI [39]. There are only a few studies investigating cultural background and GWG and they are commonly from the United States comparing racial differences between Hispanic, white and black women [40, 41]. The recent series in the Lancet on maternal obesity has called for more ethnic and culturally specific research [42]. Cultural background may be an important determinant for GWG, and due to increasing globalisation and migration, it is difficult to ascertain whether any relationship is due to cultural background per se or the result of assimilation into a new environment and culture. Furthermore, there are no current ethnic specific guidelines with regards to healthy GWG. A recent study from Singapore showed that there may be a variation in terms of weight gain recommendations and adverse outcomes specific to those of an Asian ethnicity [43]. Further research is needed to examine whether ethnic specific recommendations for GWG need to be developed and whether there are any specific cultural beliefs that may influence GWG for different ethnic groups.

The strengths of this study is the large number of participants, the inclusion of participants from a number of hospitals (both secondary and tertiary) and the diverse ethnic and cultural backgrounds making these results generalisable to the diverse multicultural Australian population [44]. The inclusion of a multivariable regression analysis assesses a significant association between obese, low SES and excess early gestational weight gain.

A limitation of this study was the use of self-reported pre-pregnancy weight and height, although this has been shown to have adequate correlation with measured height and weight [45]. These results may not be generalisable to other perinatal centres with a distribution of maternal ethnic representation in Australia. There are no current ethnic specific guidelines with respect to ideal weight gain in pregnancy. We could not be certain of specifically when women gained significant weight, whether it be in their first trimester or second trimester therefore we assumed that women gained up to 2 kg in their first trimester and then the weight beyond that can be calculated to be their weekly weight gain.

Women are gaining weight in early pregnancy outside the recommendations of the IOM, which have been accepted in Australia as the guideline for healthcare professionals to use when counselling women. The women at particular risk of excess early GWG are those who are overweight and obese and women residing in lower SES areas. These women need to be targeted for appropriate counselling preconception or in early pregnancy. This study also suggests that their remains a lack of understanding of healthy weight gain recommendations in early pregnancy, where weight gain has a significant impact on short-term pregnancy outcomes and also long-term consequences for both the mother and child. Given the significant adverse outcomes associated with excess GWG in early pregnancy, preconception or early pregnancy counselling with respect to GWG and intervention research regarding best approach remains a public health priority.