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Findings

Canadian women’s adherence to Health Canada’s gestational weight gain guidelines has not been assessed since the recommendations were released in 1999.¹ Observational studies in countries with similar guidelines have shown that women tend to gain more weight than recommended while they are pregnant.^2-5 The release of perinatal health data⁶ for a representative sample of Canadian women provides an opportunity to determine if women in Canada also gain more weight than is recommended.

This article describes Canadian women’s adherence to Health Canada’s 1999 gestational weight gain guidelines, based on an analysis of data from the 2006 Maternity Experiences Survey (see The data). These guidelines for singleton pregnancies vary according to the mother’s pre-pregnancy body mass index (BMI). At the time of the survey, the recommended weight gain ranges were:

• 12.5 to 18.0 kilograms for women with a pre-pregnancy BMI less than 20;
• 11.5 to 16.0 kilograms for women with a pre-pregnancy BMI of 20 to 27; and
• to 11.5 kilograms for women with a pre-pregnancy BMI greater than 27.1

The ranges were adapted from the 1990 Institute of Medicine gestational weight gain recommendations,⁷ which were under review at the time of the analysis.⁸

The findings are reported according to whether the gestational weight gain was below, within or above the recommendations, by selected socio-demographic and maternity characteristics of the mother: pre-pregnancy BMI; age; parity (number of times the woman had given birth, including stillbirths); education; household income; Aboriginal status; country of birth; and region of residence.

Results are also presented for two health outcomes―post-partum weight retention and infant birth weight―for the three gestational weight gain categories.

Factors associated with gestational weight gain

According to the 1990 Institute of Medicine report, a woman’s pre-pregnancy weight is a primary determinant of how much weight she will gain while she is pregant.⁷ Indeed, results from the Maternity Experiences Survey show that 55% of overweight women gained more than recommended while they were pregnant, compared with 41% of those who were in the normal range and 26% of those who were underweight (Figure 1). However, in addition to pre-pregnancy weight, factors such as age, parity, education and income have also been identified as potential predictors of weight gain during pregnancy.^21,22

Figure 1
Percentage of women who gained less than, within and more than Health Canada's gestational weight gain guidelines, by pre-pregnancy body mass index (BMI), female household population aged 15 or older who gave birth during three months before 2006 Census, Canada

The percentage who gained more weight than recommended declined at older ages, from 56% of 15- to 19-year-old mothers to 35% of those aged 35 to 39 (Table 1).

Table 1
Percentage of women who gained less than, within and more than Health Canada's gestational weight gain guidelines, by selected characteristics, female household population aged 15 or older who gave birth during three months before 2006 Census, Canada

Women giving birth for the first time (primiparous) were more likely than those who had previously given birth (multiparous) to gain more than recommended: 47% versus 37%. This difference persisted when other variables, including age, were taken into account. Primiparous women’s adjusted odds of exceeding rather than being within the weight gain recommendations were 1.5 (95% CI of 1.3 to 1.7) times those of multiparous women (data not shown).

The likelihood of gaining more weight than recommended during pregnancy was greater among women with less than secondary education (53%), compared with those who had some postsecondary education (43%) or a university degree (38%). This difference held when other factors were taken into account. The adjusted odds that women with less than secondary education would exceed rather than be within the weight gain recommendations were 2.1 (95% CI of 1.6 to 3.0) times those of women with a university degree (data not shown).

On the other hand, women with a low household income were no different from those with a high household income in terms of gaining more weight than recommended (43% versus 41%) during pregancy. However, a higher percentage of women with a low household income gained less than recommended, compared with women who had a high household income (27% versus 21%).

Women who self-identified as Aboriginal were more likely than non-Aboriginal women to gain more than recommended: 55% versus 44%. And owing to post-partum weight retention, excess weight gain during pregnancy has the potential of further exacerbating the current high prevalence of overweight and obesity among Aboriginal women²³ living off-reserve.

A higher percentage of women born in Canada (44%) gained more weight than recommended during their pregnancy, compared with women not born in Canada (33%).

Among the six regions, Ontario’s percentage distribution of weight gain during pregnancy in relation to the Health Canada recommendations was very close to the distribution for Canadian women overall. And compared with Ontario, only in the Atlantic region did a significantly higher percentage of women gain more weight than recommended while they were pregnant.

Gestational weight gain and health outcomes

The weight gain guidelines reflect observations of healthy pregnancy outcomes.⁷ Gaining insufficient weight has been associated with low birth weight (less than 2,500 grams), while gaining too much weight has been associated with both high birth weight (more than 4,000 grams) and post-partum weight retention.²⁴

According to the Maternity Experiences Survey, women who gained less weight than recommended when they were pregnant were more likely to have an infant weighing less than 2,500 grams than a normal weight full-term infant: 44% versus 24% (Table 2). On the other hand, the majority (58%) of women who gained more weight than recommended gave birth to an infant weighing 4,000 grams or more. These findings mirror results from a systematic review by Viswanathan et al,²⁴ who found moderate-to-strong evidence of an association between gestational weight gains below the 1990 Institute of Medicine recommendations and low birth weight, and strong evidence to support an association between gains above the recommendations and high birth weight.

Table 2
Percentage of women who gained less than, within and more than Health Canada's gestational weight gain guidelines, by baby's birth weight, female household population aged 15 or older who gave birth during three months before 2006 Census, Canada

Five to nine months after they had given birth, women who gained more weight than recommended during their pregnancy retained more weight (an average of 4.5 kg) than did women who gained within or less than the recommendations (averages of 2.0 kg and 0.5 kg, respectively) (Table 3). Viswanathan et al ²⁴ also found moderate evidence supporting an association between weight gain above the Institute of Medicine recommendations and post-partum weight retention three months to three years later.

Table 3
Average weight retention of women who gained less than, within and more than Health Canada's gestational weight gain guidelines, by pre-pregnancy body mass index, 5 to 9 months postpartum, female household population aged 15 or older who gave birth during three months before 2006 Census, Canada

Conclusion

Information from the 2006 Maternity Experiences Survey suggests that relatively high percentages of women who are young, primiparous, less educated or Aboriginal gain more weight than recommended while they are pregnant.