Excessive gestational weight gain (GWG), even among women of normal weight before pregnancy, has been associated with short- and long-term adverse maternal and infant outcomes (12). A large GWG has been linked to postpartum weight retention, which, in turn, has been associated with long-term risk of maternal obesity (10,23,28,31,32). A prospective cohort study of 1300 women who had two consecutive births showed that 11% of normal-weight women who gained excessive weight during their first pregnancy were overweight by the second pregnancy (10). Similarly, data from a prospective cohort that observed 688 women into the postpartum period showed that, among women who were normal weight before pregnancy, 14.2% became overweight and 3.9% obese by 1 yr postpartum (32). Excessive GWG is directly associated with infant weight and adiposity at birth in women of normal weight before pregnancy (4,6,19,23,33), which increases the infant’s risk of becoming overweight/obese later in life (4,23,24,29). Because up to 40% of normal-weight women gain excessive weight during pregnancy (3,4,18), prevention of excessive GWG is of paramount importance to reduce the risk of long-term obesity and associated comorbidities in both the mother and infant.
Previous lifestyle intervention studies aimed at preventing excessive GWG in normal-weight women through a combination of exercise and dietary counseling have reported conflicting results (2,15,25–27). Factors that may explain the disparity in results may include parity, prepregnancy fitness levels of the women, their usual daily intake and eating habits, the intensity of the intervention (i.e., phone-based, mail-based, or supervised intervention, and the frequency of the counseling sessions), and the intensity of the exercise. Although previous studies indicated that their participants engaged in exercise of moderate intensity, neither physical activity level nor exercise intensity was monitored or reported during the interventions (2,15,25–27). The American College of Sports Medicine (1) suggests that the minimum intensity necessary to provide health benefits in previously sedentary women is equivalent to 20%–39% oxygen consumption reserve, which corresponds to approximately 13%–33% HR reserve (HRR) (5). We therefore chose 30% HRR (low intensity (LI)) to correspond to the minimum intensity needed to produce health benefits for a weight bearing exercise program in our pregnant population and 70% HRR (moderate intensity (MI)) to correspond to the intensity recommended in the Canadian guidelines for exercise in healthy pregnancy (34).
The objective of the present study was to evaluate the effects of a supervised LI versus a MI weight bearing exercise program in women of normal weight before pregnancy, combined with nutritional control, on GWG, infant birth weight, and maternal weight retention at 2 months postpartum. We hypothesized that women participating in the interventions would gain less weight during pregnancy and retain less weight postpartum compared with women not participating in the interventions. Further, we hypothesized that a nutrition and MI exercise program would have a greater impact on limiting excessive GWG and weight retention versus a nutrition and LI exercise intervention in normal-weight pregnant women.
Seventy-three normal-weight pregnant women (prepregnancy body mass index (BMI) = 18.5–24.9 kg·m−2 ) between 16 and 20 wk gestation were recruited through referrals from medical professionals, posters, and advertisements in newspapers in London, Ontario, Canada. Before being enrolled in the study, women were medically prescreened (PARmed-X for Pregnancy ) by their health care professional. Specific exclusion criteria included the following: maternal age <18 yr or >40 yr, smoking, multiple pregnancy, presence of chronic disease, or other contraindications to exercise (35).
Forty-five women, 2 months postpartum, were also recruited through referrals from their medical professionals, posters, and advertisements in newspapers in London, Ontario, Canada, and were considered as a historical control group. Inclusion criteria were the same as for the intervention group, except that the women should not have participated in any structured exercise program during pregnancy. Ethics approval was obtained from the Human Research Ethics Board for Health Sciences at The University of Western Ontario, and written informed consent was obtained from all participants.
Protocol to determine exercise intensity in the intervention groups.
After medical prescreening, the MI and LI participants completed a peak exercise test to volitional fatigue on a treadmill (Precor C942, Precor, Woodinville, WA) as previously described (21). After the completion of the peak test, each woman was randomized using a randomized/block procedure with four subjects per block into either the LI (30% HRR) or MI (70% HRR) group, with similarly controlled dietary intake. Peak test results were used only to determine the participants’ specific target HR zone, corresponding to 30% HRR or 70% HRR for prescription of exercise (21).
Walking exercise program.
The intervention groups walked at their calculated target HR zone of 30% HRR or 70% HRR three to four times per week. At each exercise session, participants wore a HR monitor (Polar Pacer, Sark Products, Waltham, MA) to ensure they were exercising within the predetermined target HR zone. The first week consisted of 25 min of walking per session (5 min of warm-up, 15 min at target intensity and 5 min of cool down). Each subsequent week thereafter, the time at the prescribed intensity increased by 2 min, until a maximum of 30 min was reached, plus 5 min of warm-up and 5 min of cool-down. This duration was then maintained until the end of the program. Participants were required to attend at least one exercise session per week at the laboratory to monitor adherence to the exercise intervention and to determine the weekly GWG. The participants were expected to complete an additional two to three exercise sessions by their own at the prescribe intensity. All nonsupervised exercise sessions were recorded in a home exercise log.
During the intervention, each participant followed a modified gestational diabetes meal plan to control nutritional intake, as previously described (22). To prevent excessive GWG, the specific goals as indicated by the modified gestational diabetes meal plan were as follows: 1) to individualize the total daily energy intake recommendation to favor progressive weight gain (approximately 8360 kJ·d−1 (2000 kcal·d−1)); 2) to individualize the daily CHO intake to 40%–55% of total energy intake while distributing CHO intake throughout the day with three balanced meals and three to four snacks per day, emphasizing complex CHO and low-glycemic index foods; 3) to individualize the total daily fat intake to 30% of total energy intake (substituting monounsaturated and polyunsaturated fatty acids for saturated and trans–fatty acids), with the remaining 20%–30% of energy intake dedicated to protein; and 4) to meet daily micronutrient and fluid recommendations during pregnancy (11). At study entry, before the women were taught the meal plan, a 24-h dietary recall was undertaken to assess preintervention nutrition habits. During the intervention, all women were asked to complete a food intake record 1 d·wk−1, to examine dietary adherence, and to give individualized feedback to each woman as needed (8). At the end of the intervention, a final 24-h dietary recall was collected between 34 and 36 wk of gestation. Nutrition analyses reported in the article were based on the preintervention and postintervention 24-h dietary recalls. The 24-h dietary recall is a validated tool for assessing adequacy of nutrient intake (7). Nutrition data were analyzed using the ESHA Food Processor SQL software (ESHA Research, Salem, OR), including the Canadian Nutrient File.
Self-reported prepregnancy weight and height were used to calculate prepregnancy BMI. Body weight recorded at the time of the peak exercise test was considered the preintervention weight. Women were weighed in the laboratory on a weekly basis. Body weight was rounded to the nearest 0.1 kg (Health o meter, Alsip, IL). Newborn birth weight and length were recorded from medical records and complications during delivery were obtained from maternal recall within 6–18 h after delivery. At 2 months postpartum, the women returned to the laboratory to be weighed. For the historical control group, maternal and infant characteristics were obtained from a questionnaire completed by the women at 2 months postpartum. Body weight of the control women was measured at 2 months postpartum at the laboratory.
The primary analysis compared the two randomized intervention groups using a per-protocol analysis. The effects of the intervention on GWG and weight retention at 2 months postpartum between the groups were performed by ANCOVA where GWG and weight retention at 2 months postpartum were the dependent variable, group (LI vs MI) was the fixed effect and prepregnancy body weight the covariate. A χ2 test was performed on the percentage of women who gained an excessive amount of pregnancy weight comparing the two intervention groups. Excessive total GWG was defined according to the revised guidelines for GWG published by the Institute of Medicine (IOM) (12). These guidelines recommend that women who enter pregnancy at a normal weight (BMI of 18.5–24.9 kg·m−2) should gain 11.5–16.0 kg, with weekly rates of weight gain of 0.4–0.5 kg·wk−1 during the second and third trimesters. Thus, we considered excessive GWG during the intervention (which occurred during the second and third trimesters) as average weekly rates of weight gain >0.5 kg·wk−1. Finally, we defined excessive GWG before the intervention. The maximum weight gain recommended for the first trimester (ending at 12 wk of gestation) is 2.0 kg (12). Given that our participants did not start our intervention program until 16–20 wk, we accounted for the recommended weight gain of 0.4–0.5 kg·wk−1 in normal-weight women after the first trimester. Thus, we defined excessive GWG before the intervention as 2.0 kg plus 2.0–4.0 kg (depending on when the women started the intervention program (between 16 and 20 wk). Weight retention was calculated as body weight at 2 months postpartum minus prepregnancy body weight. Similarly, a χ2 test was performed on the percentage of women who retained ≤2.0 kg at 2 months postpartum (18,26). The effect of the intervention on infant birth weight was evaluated using an ANOVA. A χ2 test was performed on the percentage of babies born weighing <4000 versus ≥4000 g and <2500 versus ≥2500 g. Because there were no significant differences in maternal and infant outcomes between the two randomized intervention groups, a secondary analysis comparing the three groups (control vs LI vs MI) was performed as described previously. Differences in descriptive characteristics between the three groups were tested using ANOVA. Analyses were performed with SAS (SAS Institute, Cary, NC). All data were expressed as means ± SD unless otherwise stated, and significance was accepted at P ≤ 0.05.
Based on previous intervention studies, approximately 52% of normal-weight women who did not participate in any intervention during pregnancy (i.e., the control groups) gained above IOM recommendations (25–27). We therefore expected that approximately 50% of the women in our control group would gain above the IOM guidelines. We considered that a decrease in excessive GWG of 20% (from 50% to 30%) would be clinically significant in the intervention group. We therefore defined a successful intervention program with no excessive GWG during the intervention to be ≥70% of the participants.
Forty-nine of the 73 participants completed the intervention. Before randomization, seven women decided to withdraw after the peak exercise test, eight women (MI group, n = 4; LI group, n = 4) dropped out because of reasons unrelated to exercise, nine women (MI group, n = 3; LI group, n = 6) dropped out because of time commitment concerns, leaving 26 women in the MI group and 23 women in the LI group. No differences in participant descriptive characteristics were observed between the three groups (Table 1). Women who dropped out of the intervention program were not significantly different from those who remained in the program in terms of age, parity, prepregnancy body weight, eating habits, or physical fitness level (results not shown).
Exercise and nutrition programs.
Women participated in the intervention for a mean duration of 21.5 ± 2.0 wk. The participants in the LI group exercised at a HR of 118 ± 8 bpm (∼31% HRR) compared with the mean HR of 139 ± 7 bpm (∼66% HRR) for the MI group (P < 0.0001) during their exercise sessions (Table 2). The number of exercise sessions performed by the women during the intervention was not different between the groups (LI = 36 ± 17 sessions, MI = 44 ± 26 sessions, P = 0.20).
Dietary intake recall analyses showed no differences in daily total energy intake, CHO intake, protein intake, and fat intake between the groups at study entry (Table 2). From before to after the intervention, no changes in total energy, protein, and fat intakes were found in any of the groups, but both groups presented a decrease in CHO intake (LI = −31.5 ± 101.3 g, P = 0.03; MI = −31.0 ± 83.6 g, P = 0.03). As a percentage of total energy intake, CHO intake decreased (−5% ± 8%, P = 0.002) and fat consumption increased (+4% ± 7%, P = 0.003) from before to after intervention in the MI group but not in the LI group.
Maternal GWG during the entire course of pregnancy was similar (P = 0.72) in both intervention groups: 15.3 ± 2.9 and 14.9 ± 3.8 kg in the LI and MI groups, respectively (Table 3). When comparing the three groups, women in the control group gained more weight during pregnancy (18.3 ± 5.3 kg) compared with those in the LI (P = 0.01) and MI groups (P = 0.003). Based on the IOM guidelines, the percentage of women who did not gain excessively during the entire course of pregnancy was 47% in the control group, 65% in the LI group and 69% in the MI (χ2 = 4.72, P = 0.32; Fig. 1). However, although on our intervention, excessive GWG was prevented in 70% of the women in the LI group and 77% of those in the MI group, mean GWG on the intervention was similar in both LI and MI groups: 10.4 ± 2.1 and 10.3 ± 2.9 kg, respectively, with weekly rates of weight gain of 0.49 ± 0.1 and 0.47 ± 0.1 kg·wk−1 (Table 3). Moreover, excessive GWG occurred before the intervention began at 16 to 20 wk of gestation in both intervention groups because 48% of the women in the LI group and 42% of those in the MI group gained excessive weight by study enrollment.
At 2 months postpartum, maternal weight retention was similar between both intervention groups (Table 3). Comparing the three groups, maternal weight retention was higher in the control group (7.2 ± 3.8 kg) compared with the MI group (4.6 ± 3.3 kg, P = 0.005) but not different from the LI group (5.4 ± 3.9 kg, P = 0.06). Only 7% of the women in the control group retained ≤2.0 kg compared with 28% of those in the MI group (χ2 = 5.97, P = 0.02) and 18% of those in the LI group (χ2 = 2.09, P = 0.15). No differences were found between the LI and MI groups (χ2 = 0.63, P = 0.43).
Gestational age at delivery, infant birth weight, length, ponderal index, and BMI were similar between the three groups (Table 4). The number of babies born weighing 4000 g or more was similar between the three groups. Only one baby, born full-term, weighted <2500 g (MI group).
The present study examined the effects of a 22-wk prenatal exercise program of LI versus MI, with nutritional control, on GWG, infant birth weight, and maternal weight retention at 2 months postpartum. Our main findings were that a structured lifestyle intervention was ≥70% successful at preventing excessive weight gain and that increasing the exercise intensity did not increase benefits, suggesting that any exercise intensity from low to moderate, combined with health eating habits, is beneficial during pregnancy in normal-weight women. Our results also showed that our prenatal lifestyle intervention decreased weight retention at 2 months postpartum, although the reduction was greater in the moderate-intensity group. Further, we found that excessive GWG occurs early in pregnancy, highlighting the need to promote weight gain guidelines earlier than 16–20 wk and in women planning to become pregnant.
Few studies have examined the effects of a lifestyle intervention on the prevention of excessive GWG in women who are normal weight before pregnancy. Among the studies that combined physical activity and nutrition, three studies were successful at preventing excessive GWG, based on the IOM recommendations (25–27). Polley et al. (27) reported that 67% of normal-weight women who received a biweekly newsletter regarding appropriate weight gain, healthy eating, and exercise did not gain excessive GWG compared with only 42% of those who received standard prenatal care (P < 0.05). A similar intervention was able to prevent excessive GWG in women of low socioeconomic status (25). Excessive GWG was prevented in 71% of the women in the intervention group compared with 55% of those in the historical control cohort (25). In addition, Phelan et al. (26) found that 60% of normal-weight women who participated in a low-intensity, partially mail-based behavioral intervention targeting dietary intake, physical activity, and weight monitoring did not gain excessively compared with 48% of those receiving prenatal standard care (P < 0.05). Although these lifestyle interventions were able to prevent excessive GWG in 60%–70% of the women, our results show that our intervention program was more successful. Indeed, although on our intervention, weekly rates of weight gain were within the recommended guidelines of 0.4–0.5 kg·wk−1 for normal-weight women during the second and third trimesters (12) and at least 70% of the women did not gain excessively. Although two women in the LI group and four women in the MI group gained below IOM recommendations, these women delivered healthy infants of normal weight (i.e., 2500–4000 g). Our findings therefore indicate that our lifestyle program, based on a structured intervention (i.e., face-to-face) and including the prescription of a healthy meal plan, with individualized nutrition counseling provided on a regular basis throughout pregnancy, combined with a supervised walking program of determined intensity, is likely the best intervention to reduce excessive GWG.
When examining weight gain throughout the course of pregnancy, we found that the percentage of women who did not gain above the IOM guidelines was 65% in the LI group, 69% in the MI group, and 47% in the control group. In addition, we found that 45% of the women had already gained excessive weight before our intervention began, with a mean weight gain of 4.7 ± 2.6 kg, which is more than the 3.3 ± 0.6 kg (P < 0.05) that they should have gained by study enrollment. Thus, given that women gained excessive weight at the start of pregnancy, the promotion of healthy lifestyle habits and healthy weight gain during pregnancy must be provided earlier, when the women are thinking of becoming pregnant. Also, lifestyle interventions similar to the present one would be of increased benefit if started earlier in pregnancy, as soon as the risk of miscarriage is low (i.e., at the start of the second trimester—week 13).
The novelty of the present study is that we showed that increasing the intensity of the exercise program from a low to a moderate level did not influence GWG. This finding was surprising as both groups had different energy expenditures (they were not exercising at the same intensity) but reported similar total energy intake. The MI group likely had a lower energy in/energy out ratio than the LI group and should have gained less weight during the intervention. A possible explanation of our finding may be compensation for the energy expenditure during the exercise sessions through a reduction in energy expenditure from nonexercise activity thermogenesis (NEAT) (13). NEAT is defined as the energy expenditure of all physical activities other than volitional exercise, such as the activities of daily living, small muscle movements, spontaneous muscle contraction, and postural maintenance (17). It has been reported that NEAT was reduced after more intense exercise sessions in nonpregnant individuals (9,16), and this phenomenon was partially explained by greater exercise-induced fatigue and discomfort. Perhaps fatigue and discomfort related to pregnancy may be exacerbated by the addition of an exercise regimen of higher intensity, favoring a reduction in NEAT on exercising and/or nonexercising days. However, because NEAT was not measured in the present study, more research is needed to further examine whether the intensity of exercise performed by pregnant women may influence NEAT.
Another possible explanation for the similar GWG in both intervention groups may be an increase in total energy intake in response to an exercise-induced energy deficit, a compensation that is likely greater after higher-intensity compared with a lower-intensity exercise sessions (14). Although both groups reported similar total daily energy intakes from before to after intervention, it is possible that women in the MI group may have increased their total energy intake to compensate for greater exercise-induced energy deficit and underreported their food intake. Surprisingly, although both groups received the same healthy meal plan and nutrition counseling, a decreased percentage of CHO intake and an increase in percentage of fat intake was observed in the MI group but not in the LI group. This may partially explain why weight gain was similar between the groups. Our finding may also suggest that the intensity of exercise influences food choices. More research is needed to further examine why increasing exercise intensity from a low to a moderate level during pregnancy did not influence GWG. Given that pregnancy is a critical period for short-term and long-term body weight regulation and that the success of lifestyle interventions aimed at preventing excessive GWG is mixed, research investigating possible compensatory behaviors to exercise interventions in pregnant women, and how exercise intensity may influence these behaviors, may help design successful interventions.
Gaining excessively during a normal-weight pregnancy and retaining weight after delivery increases the risk of overweight and obesity (10,23,28,31,32). In the present study, we found that 28% of the women in the MI group were already within 2.0 kg of prepregnancy body weight at 2 months postpartum compared with only 7% in the control group, suggesting that our prenatal lifestyle intervention was successful at decreasing weight retention in early postpartum. Among the women in the MI group who were within 2.0 kg of prepregnancy body weight at 2 months postpartum (n = 7), two gained below and five gained within IOM recommendations, indicating that those who gained excessively were all above 2.0 kg of prepregnancy body weight at 2 months postpartum. This finding is in agreement with studies showing an association between excessive GWG and greater postpartum weight retention (18,28). Although our data suggest that exercising at MI during pregnancy may have a greater effect on the prevention of gestational weight retention at 2 months postpartum, further research is needed to examine whether this exercise intensity effect lasts beyond 2 months postpartum. The study of Phelan et al. (26), which was successful at reducing excessive GWG in normal-weight women, reported increased percentages of women who achieved their preconception weight (±0.9 kg) or were below at 6 months postpartum (odds ratio = 2.1, 95% confidence interval = 1.3–3.5, P = 0.005). Weight retention at 6 months postpartum was 2.1 ± 4.7 kg in the intervention group versus 3.3 ± 3.5 kg in the control group, with 36% of the women in the intervention group being at or below their prepregnancy body weight compared with 21% of those in the control group. However, 36% is a fairly low number, especially because weight retention at 6 months postpartum is a strong predictor of long-term weight retention (28). We chose to examine weight retention at 2 months postpartum because the early postpartum period, after the initial weight loss that occurs after delivery (i.e., by 6 wk postpartum), may be a critical time for the assessment of weight retention. This period is when many women have their first postnatal medical examination, providing an opportunity for health care providers to reinforce healthy lifestyle changes in the early postpartum period to prevent weight retention. In addition, we decided to use the cutoff of 2.0 kg of prepregnancy body weight at 2 months postpartum to be stringent. Indeed, Statistics Canada reported that normal-weight women who gained within the IOM recommendations retained 2.2 kg at 5–9 months postpartum (18). In addition, a mean weight retention of 2.1 kg at 6 months postpartum was reported by Phelan et al. (26) in normal-weight women who participated to their prenatal intervention. Because the present study and that of Phelan et al. did not assess weight retention at the same postpartum age, it is not possible to compare the effectiveness of the two studies on weight retention. In addition, although these findings support the importance of promoting a healthy lifestyle during pregnancy to reduce postpartum weight retention, further studies are needed to examine the effect of such interventions on the prevention of obesity in the long term (i.e., beyond the postpartum period), especially considering the weight gain patterns of women during their childbearing years.
Finally, GWG is directly associated with infant weight and adiposity at birth (4,6,19,23,33) and with an increased risk of overweight/obesity later in life (4,23,24,29), suggesting that limiting excessive GWG might have an impact on the prevention of long-term obesity risk in the offspring. Although the present study was successful at limiting GWG, we did not find an effect on infant birth weight, which agrees with previous studies including normal-weight women (25–27). In the present study, one women gave birth to a baby born full term, weighting <2500 g. The woman was in the MI group and gained above IOM recommendations. Larger prenatal lifestyle intervention studies are needed to detect the effect of limiting excessive GWG on infant birth weight.
The present study has several strengths, including the combination of a supervised exercise program with nutrition control, the randomization of the participants in two exercise intensities, the use of personalized target HR based on data from the peak test performed at study entry, weekly GWG monitoring from the second trimester until delivery, and follow-up at 2 months postpartum. Because overwhelming evidence showed that excessive GWG and weight retention, even in normal-weight women, are associated with short- and long-term adverse maternal and infant outcomes, we chose to use a historical cohort of women who did not participate in any structured exercise program during pregnancy. Control women did not differ from those in the two intervention groups in terms of prepregnancy BMI, age, and parity, which are important factors that may influence GWG, birth outcome, and postpartum weight retention (20).
Our study also presents limitations that need to be addressed. First, we used self-reported prepregnancy body weight and may have therefore overestimated total GWG and weight retention at 2 months postpartum. However, self-reported prepregnancy weight has been shown to approximate the true value (r = 0.99) (24). Delivery body weight of historical controls was also self-reported but maternal recall of GWG and self-reported delivery weight 6 months to 2.5 yr after delivery have been reported to be highly correlated with that documented in medical records (30). Second, dietary recalls were done for 1 d at the beginning and at the end of the study. Given that it is recommended to have at least 2 d of dietary intake (11), the information we have may not fully reflect the usual dietary intake habits of the participants. Also, a more detailed dietary assessment would be helpful to analyze the dietary intake patterns of women during pregnancy. Finally, the average number of exercise sessions reported per week during the intervention (i.e., 1.7 and 2.0 for the LI and MI groups, respectively) probably does not truly reflect the number of times they actually exercised per week. Indeed, we may have missed information about the nonsupervised exercise sessions performed by the participants because some women forgot to record their exercise sessions on the home exercise log, forgot to hand them in, or were away on vacation. Among the women who did complete their home exercise log, those in the LI group had a total of 52 ± 10 exercise sessions (2.5 wk−1) and those in the MI group 63 ± 23 exercise sessions (3 wk−1) and these numbers may better reflect what actually occurred during the study. However, we have no way to document this. Thus, the limitation of our study is not that the women were not compliant with the exercise program but rather we may have missed information not recorded in home exercise logs.
In conclusion, we have demonstrated that a prenatal exercise and nutrition intervention prevented excessive weight gain and decreased weight retention at 2 months postpartum in women with normal prepregnancy weight. Further, we found that increasing the intensity of exercise from a low to a moderate level did not influence GWG, suggesting that participating in a LI or MI exercise program, combined with healthy eating habits, is an important component of a healthy pregnancy. Our observation that excessive GWG occurs early in pregnancy highlights the need to promote healthy lifestyle habits and provide weight gain recommendations as soon as the women are thinking of becoming pregnant.
The study was supported by the Lawson Research Foundation and the Canadian Institutes of Health Research, Institute of Aboriginal Peoples’ Health. S.M. Ruchat was supported by a postdoctoral fellowship from the Canadian Diabetes Association. M.H. Davenport was supported by a doctoral research award from the Canadian Institutes of Health Research.
The authors have no conflicts of interest to declare.
The results of the present study do not constitute endorsement by the American College of Sports Medicine.
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