The effects of physical exercise on pregnancy remain to be elucidated. A randomized controlled trial will be conducted to study the impact of exercise on maternal and perinatal outcomes. Our hypothesis is that physical exercise reduces preeclampsia incidence and improves birthweight when started early in pregnancy, with no impact on pregnancy duration, Apgar scores and neonatal complications.

The study will include low risk pregnant women randomized to practice physical exercise beginning at 13 weeks, 20 weeks or no exercise group.

The objectives are:

1. To describe and compare biological and obstetrical variables.
2. To study doppler flow velocimetry indexes.
3. To determine the association between physical exercise and maternal complications: preeclampsia, preterm labor, gestational diabetes and weight gain in pregnancy.
4. To determine the association between physical exercise and perinatal outcomes: Apgar scores, birthweight, admission at intensive neonatal care unit, body composition and neonatal complications.

Inclusion Criteria:

• Gestational age < 13 weeks
• Single pregnancy
• Alive fetus
• No previous practice of physical activity

Exclusion Criteria:

• Smoking
• Chronic maternal diseases
• Placenta praevia
• History of preterm labor
• Bleeding