By the second trimester of pregnancy, an extra 1.3 MJ (300 kcal) per day are required to meet general metabolic needs in pregnancy, and this energy requirement is increased with exercise. Pregnant women use carbohydrates at a greater rate than do nonpregnant women—both at rest and during exercise—and there is preferential use of this form of energy during non-weight-bearing exercise, making adequate carbohydrate intake of particular importance.
Although routine prenatal care is sufficient for monitoring women in average exercise programs, closer obstetric observation is required for women who are elite athletes.
Most elite athletes choose to continue training during pregnancy, but they must be told that they probably will not achieve the same level of performance as they did before pregnancy, and the physiologic changes they experience—such as weight gain and joint or ligament laxity—will also make them more prone to injury. Women engaging in endurance sports can be prone to anemia that results from increased blood volume during pregnancy. High intensity, prolonged, and frequent exercise can put women at greater risk of thermoregulatory complications as well, and will usually result in less maternal and fetal weight gain than occurs in less active women.
The American Diabetes Association has endorsed exercise as a helpful adjunctive therapy for gestational diabetes mellitus (GDM) when glycemic control cannot be achieved through diet alone. Approximately 39% of patients with GDM require insulin therapy, but in my experience, exercise is a safe and effective alternative for most of these women.
The key to achieving euglycemia through exercise is ensuring the adequate duration and intensity of the activity. Exercise improves the impaired insulin sensitivity of women with GDM, which in turn increases glucose uptake by muscles and splanchnic organs, but this effect is achieved only through the activation of large muscles, such as the quadriceps, at adequate intensity, which explains why some studies in the literature fail to show normalization of glucose levels after exercise. At least half an hour of brisk walking per day is sufficient to upregulate insulin sensitivity in patients with GDM, obviating the need for insulin therapy.
Additionally, epidemiologic data suggest that exercise may act as primary prevention for GDM in morbidly obese women, but not in women of normal weight.
Although exercise should never be used for weight control during pregnancy, excessive weight gain should be avoided.
The current Institute of Medicine (IOM) guidelines on weight gain—which recommend a gain of 25–35 pounds for normal-weight women with a singleton pregnancy—are too high and are based on historical concerns about the effects of famine on fetal growth retardation.
The effect of gestational weight gain on pregnancy outcomes in obese women is not well studied. It is my opinion that the IOM guidelines are outdated, and that weight gain recommendations should be individualized. Compared with IOM recommendations for adequate gestational weight gain in obese women (at least 15 pounds), it is well recognized that a gain of less than 15 pounds in this population significantly reduces the risks of preeclampsia, C-section, and large-for-gestational-age infants.
The risk for small-for-gestational-age infants varies significantly, particularly among morbidly obese women in whom no weight gain—or even weight loss—may not have any adverse effect on birth weight.
Because failure to lose weight gained in pregnancy is a significant contributor to the obesity epidemic, the promotion of good exercise habits during pregnancy can also sow the seeds for postpartum exercise and weight loss.
One study showed that the amount of postpartum weight retention increases with each subsequent pregnancy (Acta. Obstet. Gynecol. Scand. 1979;58:45–7). Another study found that women who gained excessive weight during pregnancy and failed to lose it within 6 months post partum were 8.3 kg heavier 10 years later (Obstet. Gynecol. 2002;100:245–52).
Our study found that a weekly structured exercise program plus diet in postpartum overweight women were much more effective in achieving weight loss after 12 weeks compared with a single 1-hour education session about diet and exercise (J. Women's Health [Larchmt] 2003;12:991–8).
Therefore, women whose exercise habits have become firmly entrenched during pregnancy stand a much better chance of maintaining them post partum—and perhaps even into their next pregnancy.
Maintenance of euhydration is essential to controlling core temperature while exercising in pregnancy. Lynda Banzi
Exercise in Pregnancy
The extraordinary increase in obesity in the United States is giving rise not only to direct complications, such as hypertension and cardiovascular disease, but also to indirect problems such as diabetes. Hence, we have one problem leading into many others, ultimately resulting in a significant increase in morbidity and mortality.