Research Updates 2006-2010

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Research in this section includes excerpts from longer works by DTP staff, including material on Maternal Metabolism, Fetal Responses, and Postpartum Physiology.

Maternal Metabolism

Exercise offsets the elevated glucose response of pregnancy by utilizing blood sugar. The evolutionary biology model is useful for understanding that an ability to store energy in pregnancy more readily than at any other time is a survival mechanism that may have evolved in early humans. Because rigorous physical demands of survival in developed countries have been essentially eliminated from contemporary life and processed foods have become a norm, it is easy to see how metabolic dysfunction in the form of hypoglycemia, hyperglycemia or diabetes is increasingly generated in pregnancy. Thus, prevention and/or management of gestational diabetes that includes healthy nutrition and exercise are well accepted.

Gestational Diabetes, Overweight & Strength Training

Overweight pregnant women with diabetes requiring insulin are able to reduce the amount of insulin they require when they participate in regular strength training three times a week or more.

Source: Brankston GN, Mitchell BF, Ryan EA, Okun NB. Resistance exercise decreases the need for insulin in overweight women with gestational diabetes mellitus. Am J Obstet Gynecol. 190(1):188-93. 2004.

There is evidence for metabolic imprinting of childhood obesity in the fetus exposed to the hormonal milieu of gestational diabetes mellitus (either with or without preexisting maternal diabetes).

Source: Wright CS, Rifas-Shiman SL, Rich-Edwards JW, Taveras EM, Gillman MW, Oken E. Intrauterine exposure to gestational diabetes, child adiposity, and blood pressure, American J Hypertension 22(2):215-220. 2009.

Further, insulin-stimulated rates of mitochondrial ATP synthesis are reduced in insulin resistant offspring of type 2 diabetic parents, and these offspring have impaired insulin-stimulated phosphate transport in muscle.

Source: Petersen KF, Dufour S, Shulman GI. Decreased insulin-stimulated ATP synthesis and phosphate transport in muscle of insulin-resistant offspring of type 2 diabetic parents, PLos Med 2(9):e233. 2005.

Regular exercise, on the other hand, exposes the fetus to the hormonal milieu associated with a physically active lifestyle. For example, levels of tumor necrosis factor alpha and leptin, metabolic markers that, among other things, reflect fat mass and insulin resistance, are both more favorable when women (and thus their fetuses) participate in regular weight-bearing exercise during pregnancy.

Source: Clapp JF III,  Kiess W. Effects of pregnancy and exercise on concentrations of the metabolic markers tumor necrosis factor alpha and leptin.  Am. J. Obstet. Gynecol. 182(2):300-306, 2000.

The American Diabetes Association (ADA) now recommends that “…people with impaired glucose tolerance should begin and continue a program of weight control, including at least 150 minutes per week of moderate to vigorous physical activity and a healthful diet with modest energy restriction (Level of evidence: A)”. In addition, unless there are contraindications, the ADA recommends people with type 2 diabetes perform resistance exercise 3 times per week, targeting all major muscle groups.

Fetal Responses

Fetal Cardiovasculature and Hemodynamics

A recent study found that the fetuses of pregnant women who participate in aerobics demonstrate a beneficial training effect, i.e., they exhibit lower resting pulses and greater variability than fetus’ of mothers who do not participate in aerobics.

Source: May LE et al. Exercise During Pregnancy Benefits Baby. Experimental Biology 2008 scientific conference; 121st annual meeting of the American Physiological Society. 2008.

The fetal heart rate normally accelerates but maintains variability during and after exercise.  Gestational age, exercise type, intensity and duration influence the extent of change in fetal heart rate during and following exercise.

Sources: Carpenter MW, Sady SP, Hoegsberg B, et al. Fetal heart rate response to maternal exertion. JAMA 259:3006-3009, 1988; • Webb KA, Wolfe LA, McGrath MJ. Effects of acute and chronic maternal exercise on fetal heart rate.  J Appl Physiol 77:2207-2213, 1994; • Clapp JF III, Little KD, Capeless EL. Fetal heart rate response to sustained recreational exercise.  Am J Obstet Gynecol 168:198-206, 1993.

A study—involving acute exercise in mothers with high trait anxiety scores–found significantly higher pulsatility index (PI) values in the umbilical artery, significantly lower PI values in the fetal middle cerebral artery and significantly lower cerebro-umbilical PI ratios, suggesting a shift in blood distribution in favor of the fetal brain in these mothers. While pregnant women who exercise benefit from stress relief, they and their fetuses receive additional benefits from fitness training effects.

Source: Sjostrom K, Valentin L, Thelin T, Marsal K. Maternal anxiety in late pregnancy and fetal hemodynamics.  Eur J Obstet Gynecol Reprod Biol. 74(2):149-155,  1997.

Fetal Movement

This 2009 study looking at fetal breathing patterns in exercises and controls found that the fetal heart rate was significantly lower in the exercise group during fetal breathing and non-breathing movement periods. In addition, fetal short-term and overall heart rate variability were higher in the exercise group during breathing movements, three independent measures of vagal control were higher in the exercise-exposed fetuses during breathing movements, and during periods of fetal non-breathing, there were no significant differences in measures of vagal control between groups.

Source: May LE, Million S, Gustafson KM. The Effects of Maternal Exercise on Fetal Breathing Movements, Experimental Biology 2009 scientific conference; 122nd Annual Meeting of the American Physiological Society. 2009.

Other studies on fetal body or breathing movements have found changes to be small, inconsistent and transient. In practice, during group exercise classes mothers seem to be most aware of fetal limb movement during relaxation, at which time they frequently report high levels of activity.  There are no reports in the literature of detrimental fetal outcomes in this regard.

Postpartum Physiology

Maternal Cardiovasculature

Women with hypertensive disorders in pregnancy are at increased risk for cardiovascular disorders over the long term. Women with a history of preeclampsia exhibit impaired endothelial function up to a year postpartum, which may be one reason they are at increased risk for hypertension and cardiovascular disease.

Source: Agatisa PK, Ness RB, Robers JM, Costantino JP, Kuller LH, McLaughlin MK. Impairment of endothelial functin in women with a history of preeclampsia:  an indicator of cardiovascular risk. Am J Physiol Heart Circ Physiol 286(4):389-393. 2004

In a matched control study, postpartum women who had preeclampsia demonstrated persistent elevated central retinal artery systolic velocity, suggesting distal vasoconstrictio.

Source: Giannina G, Belfort MA, Cruz AL, Herd JA. Persistent cerbrovascular changes in postpartum preeclamptic women:  a Doppler evaluation. Am J Obstet Gynecol 177(5):1213-1218. 1997.

Metabolism

Although women with hypertensive disorders often report significant declines in health status postpartum, women with gestational diabetes do not report declines in health status any more frequently than mothers without either of these disorders. However, there are metabolic issues for both mother and offspring that need to be addressed in part with exercise, if long-term health is a goal.

Source: Kim C,, Brawarsky P,Jackson RA, Fuentes-Afflick E, Haas JS. Changes in health status experienced by women with gestational diabetes and pregnancy-induced hypertension. J Women’s Health 14(8):729-736. 2005.

The prevalence of adequate exercise in this group is low and highly dependent on social support.

Source: Smith BJ, Cheung NW, Bauman AE, Zehle K, McLean M. Postpartum physical activity and related psychosocial factors among women with recent gestational diabetes mellitus. Diabetes Care (28(11):2650-2654. 2005.

As women with gestational diabetes are at increased risk for the development of type 2 diabetes, identification and appropriate intervention that includes exercise is important for this population.

Sources: Case J, Willoughby D, Haley-Zitlin V, Mabee P. Preventing type 2 diabetes after gestational diabetes. Diabetes Educ 32(6):877-886. 2006.  • Kjos, SL. After pregnancy complicated by diabetes: postpartum care and education. Obstet Gynecol Clinics NA 34(2): 335-349. 2007.

Determining women’s beliefs and current behaviors can provide clues to helping design effective daily exercise routines.

Source: Downs DS, Ulbrecht JS. Understanding exercise beliefs and behaviors in women with gestational diabetes, Diabetes Care 29(2):236-240. 2006.

Two strategies that include exercise are being suggested and investigated to prevent and improve adverse postpartum outcomes for overweight and obese women. One is developing weight management interventions for women early in the childbearing years as a preventative. The other is the Active Mothers Postpartum (AMP) approach, developing individualized behavior change interventions for postpartum weight loss based on the teachable moment concept.

Sources: Keller C, Records K, Ainsworth B, Permana P, Coonrod DV. Interventions for weight management in postpartum women. JOGNN 37(1):71-79. 2008.  • Ostbye T, Krause KM, Bower RJN, Lovelady CA et al. Active Mothers Postpartum (AMP): rationale, design and baseline characteristics. J Women’s Health 17(10):1567-1575. 2008.

Hopefully, these approaches to increasing physical activity in women at risk for metabolic disorders and obesity following pregnancy will yield evidence about how exercise helps reduce the risk for further problems for these women, and how target populations can be identified and become motivated to participate.