Exercise and Pregnancy

Moderate exercise has minimal risk to pregnancy

Important gaps in our knowledge of exercise and pregnancy remain. Available data suggest, however, that moderate exercise on a regular basis during a healthy pregnancy has minimal risk for women and their fetuses.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2255149/pdf/canfamphys00059-0099.pdf

Exercise during early pregnancy lowers risk of preeclampsia by 20%

1 in 4 reported that they were not physically active, whilst just under 1 in 10 women (7 percent) reported that they had taken part in more than 25 episodes of physical activity every month in the beginning of pregnancy. By comparing these two groups, it was found that women who exercised had a 20 percent lower risk for pre-eclampsia. This was particularly relevant for women with BMI (Body Mass Index) under 25. Among women with BMI over 30, this study does not show any protection against pre-eclampsia despite physical activity.

http://www.sciencedaily.com/releases/2008/11/081111102802.htm

Exercise has a protective effect on pregnancy

We have proposed the following 4 mechanisms that may explain the protective effect of exercise during gestation: enhanced placental growth and vascularity, reduced oxidative stress, reduced inflammation, and correction of disease-related endothelial dysfunction.

http://www.ncbi.nlm.nih.gov/pubmed/17213880

Having less muscle or participating in strenuous exercise may negatively impact pregnancy

Term placental system A activity (reduced in small for gestational age fetuses) was lower in women with smaller pre-pregnancy upper arm muscle area, but was not related to maternal fat mass. System A activity was lower in mothers who reported undertaking strenuous exercise, but was not associated with other maternal lifestyle factors. Lower placental system A activity in women who reported strenuous exercise and had a lower arm muscle area may reflect an adaptation in placental function which protects maternal resources in those with lower nutrient reserves. This alteration may affect fetal development, altering fetal body composition, with long-term consequences.

http://www.ncbi.nlm.nih.gov/pubmed/20206993

More muscle associated with 2x more male births, may be due to superior health

In humans, there is evidence that the physiological cost to the mother of bearing sons is greater than of bearing daughters. Parents should manipulate the sex of offspring born in response to resource availability to maximize their reproductive success. Here, we demonstrate that, within a rural food-stressed community in southern Ethiopia, there is a strong association between the sex of the most recent birth and maternal nutritional status, measured either by body mass index or mid-upper arm muscle area (measures of fat and muscle mass). The effect of muscle mass is very marked: those women in the upper 25th percentile of arm muscle area were more than twice as likely to have had a recent male birth than those in the lowest 25th percentile.

http://www.ncbi.nlm.nih.gov/pubmed/12952651

More muscle associated with higher prenatal linear growth

The following were included among the findings: 1) tall and short mothers had newborns with similar birth weight and recumbent length; 2) mothers characterized by high subcutaneous fat had heavier and fatter, but not longer, newborns than mothers with low subcutaneous fat; 3) mothers characterized by high upper arm muscle area had heavier, leaner and longer newborns tha mothers with low upper arm muscle area; 4) mothers characterized by high muscle and high fat had heavier and longer newborns than mothers with high muscle and low fat; and 5) mothers characterized by high muscle and low fat had heavier and longer newborns than mothers with low muscle and high fat. On the basis that subcutaneous fat and arm muscle area reflect calorie and protein reserves respectively, it is concluded that an increase in maternal calorie reserves results in increased infant fatness but a lesser increase in linear growth. Increase in maternal protein reserves enhances both birth weight and prenatal linear growth.

http://www.ncbi.nlm.nih.gov/pubmed/848566