There is a lot of miss information surrounding the effects of exercise in pregnant women, is it good or bad for the mother and her infant. This has been due to a lack of controlled studies.
In 2002, ACOG (American Congress of Obstetricians and Gynecologists) concluded that exercising for 30 minutes most days improved cardiovascular function and reduced the incidence of disease.
In December this year (2012), a new randomised study on the effects of exercise in pregnancy showed that subjects in the active group significantly improved their aerobic fitness and strength compared to those in the sedentary group. It also found there were no adverse effects on pregnancy length, fetal birth weight and placenta weight. There was a slightly reduced risk of gestational diabetes in the active group and no participants in the active group experienced hypertension.
It also showed those in the active group were able to return faster to household duties postpartum than those in the sedentary group.
If you are pregnant, even at 12-14 weeks it is important to remain active, exercising for 30 minutes a day, for most days.
For more information visit the ACOG link.https://www.acog.org/Search?Keyword=exercise%20guidelines