This will be an open randomized clinical trial involving pregnant women between 35 and 37 weeks randomized to two modalities of exercise: treadmill or stationary bike. The study hypothesis is that exercise on a stationary cycle causes less maternal and fetal effects in relation to treadmill exercise.We will study the acute effects of exercise for both the mother and the fetus, monitoring the parameters before, during and after exercise for 20 minutes. The exercise intensity will be moderate, remaining between 60% and 80% of maximum heart rate. Women will be monitored with a recording equipment of ABPM (ambulatory blood pressure monitorization) and continuous cardiotocography and blood will be collected to measure blood glucose, total cholesterol and HDL, nitrate and lactate before, during and after exercise. The analysis variables are: maternal heart rate and blood pressure, fetal heart rate, number of fetal movements, transient accelerations, decelerations, short-term variability, episodes of high variability, uterine tone, glucose, lactate, nitrate, total cholesterol and HDL.The analysis will be based on intention to treat, according to the recommendations of the CONSORT (2010).

Background: Exercise has been encouraged during pregnancy in order to reduce undesirable outcomes such as pre-eclampsia, excessive weight gain and diabetes. Despite widespread among pregnant women and obstetricians, little is known about the acute effects for both mother and fetus at the time of exercise, with most existing research controlling only the pre-and post-exercise.

Objective: To study the acute effects of two moderate modalities of exercise on the pregnant woman and fetus.

Methods: This will be an open randomized controlled trial to be conducted in Campina Grande, Brazil, from December 2011 to December 2012. The pregnant women with gestational age between 35 and 37 weeks will be randomized into two groups of moderate-intensity exercise: treadmill and stationary bicycle. Pregnant women and fetuses will be monitored for 60 minutes divided in three steps of 20 minutes each: baseline assessment, monitoring during exercise and recovery period. Women will be monitored using a recording equipment of ABPM (ambulatory blood pressure monitorization) and fetal heart rate will be monitored through computerized cardiotocography. Blood will be collected to measure blood glucose, total cholesterol and HDL, nitrate and lactate before, during and after exercise. The intensity of exercise will be maintained between 60% and 80% of maximum heart rate by Karvonen formula, in addition to the subjective perception of exertion on the modified Borg scale (moderate intensity). During the monitoring period (in the three moments mentioned above) blood will be collected for the measurement of glucose, total cholesterol and HDL, nitrate and lactate. The analysis variables are: maternal heart rate and blood pressure, fetal heart rate, number of fetal movements, transient accelerations, decelerations, short-term variability, episodes of high variability, uterine tone, glucose, lactate, nitrate, total cholesterol and HDL

Statistical Analysis: Statistical analysis will be performed using Epi Info 3.5.3 and Medcalc 11.6.6.0 or higher versions available at the time. The analysis will be based on intention to treat, according to the recommendations of the CONSORT (2010). For comparison of levels of glucose, lactate, cholesterol, nitrate, maternal blood pressure, maternal and fetal heart rate, fetal movements, transient accelerations, decelerations, changes in short-term episodes of high variation, and uterine tone in the two groups a parametric test will be used (Student's t) if these variables have normal distribution, otherwise they will be evaluated using the nonparametric test of Mann-Whitney. To determine the association between mode of exercise and frequency of fetal bradycardia the chi-square test of association (Pearson) will be used at a 5% significance level. The risk ratio (RR) will be calculated as a measure of relative risk, as well as its 95% confidence interval. If a significant difference in the rate of bradycardia will be demonstrated between the groups, the NNH (Number Need Harm) will be calculated.

Ethical issues: The research project was approved by Institutional Review Board under the number CAAE 0195.0.133.000-11 All the participants will be informed about the objectives of the research and only will be included if they agree voluntarily to participate and sign an informed consent term. There are no conflicts of interest.

Inclusion Criteria:

• Single pregnancy
• Alive fetus
• Gestational age between 35 and 37 weeks
• Previous sedentarity

Exclusion Criteria:

• Smoking
• Chronic maternal illness
• Diseases that affect respiratory capacity
• Physical handicap precluding performing exercise
• Arterial Hypertension
• Diabetes in Pregnancy
• Placenta praevia
• Preterm labor
• Bleeding in the third trimester
• Fetal Growth Restriction
• Oligo-hydramnios
• Brain-sparing effect
• Fetal malformations
• Medical contraindications for performing exercise