When I was pregnant with my first child, my obstetrician, as well as the pregnancy-related literature, emphasized the importance of taking prenatal vitamins and consuming a nutrient dense diet because I was "eating for two."  The premise being that a proper diet would aid in the growth and the development of the baby inside me, giving it a healthier start once born.  Exercise was discussed, but the message focused more on the maternal health benefits and the infant's weight at birth.  Current research is now looking at the importance of "exercising for two" in regard to its long-term effects on the body size of children ages 8-10 years.
Investigators from Michigan Sate University evaluated the relationship between maternal leisure time physical activity and body mass index (BMI), body fat percentage, and waist circumference (WC) during a child's pre-adolescent years.  Subjects included 20 mother/child pairs.  Height, weight, percent body fat, BMI, WC (obtained from children only), and fitness levels were assessed for the pairs.

Results of the study indicated that a mother's pre-pregnancy leisure time physical activity level was inversely related to her child's percent body fat at ages 8-10 years.  Maternal leisure time physical activity level during the second trimester also appeared to have a significant inverse correlation with child body size in reference to WC.  A trend toward this pattern was noted for maternal activity levels during the third trimester.  However, no correlation was noted between maternal exercise habits during the first trimester and child body size.  Also of note was that an inverse relationship existed between current materanl fitness and BMI, percent body fat, and WC of the pre-adolescent.

The investigators concluded that leisure time physical activity during pregnancy, particularly during the second and third trimesters, has a positive effect on child body size later in childhood (8-10 years of age). And, mothers who are more fit during the years after giving birth are more likely to have children who have lower BMI, percent body fat, and WC levels.  The researchers also suggested that their findings provide evidence that maternal physical activity during pregnancy improves the in-utero environment, making it more conducive to developing a child who will have a healthier body size during the pre-adolescent years.

Pregnant women need to not only focus on eating well for two, but on participating in healthy exercise for two. Women should consult their physician regarding the safety of exercise during pregnancy.

Note:  Before beginning an exercise program or increasingthe intensity level of a current routine, a physician's approval should be obtained, especially for older adults and those at risk for or who currently have chronic health conditions.

Source:
Sports Medicine Bulletin, "Active Voice: More Maternal Physical Activity May Lead to Leaner Pre-Adolescent Children," Pivarnik, J.M.

Medicine & Science in Sports & Exercise, Vol. 42 No. 5 Supplement Abstract 998, "Maternal Physical Activity and Child Body Size at 8-10 years," Kuffel, E.E. et al.,.