Pregnant women are recommended to be physically active ≥150 min/week, but <15% of Norwegian women attain this goal. Several well-designed studies on lifestyle interventions focusing primarily on exercise training in overweight/obese pregnant women have reported disappointing outcomes with regard to maternal glycemic control, gestational weight gain and infant outcomes. Low adherence to the training program was found to be a problem; the participants did not enjoy the exercise program and had difficulties scheduling time to exercise. Pregnant women also report that they are not sure what exercises are safe during pregnancy.

High intensity interval training (HIT), defined as short periods of intense activity separated by low-intensity breaks, has proved to induce superior improvements in insulin sensitivity and fitness compared with continuous moderate intensity training in individuals at increased risk for cardiometabolic diseases. Even short-term (6 weeks) HIT with brief (15-60 sec) work-bouts and a total time commitment of <45 min per week, improves insulin sensitivity similar to that attained after 6 months of traditional endurance training.

HIT is feasible and enjoyable for individuals with low fitness level and with obesity.

HIT is therefore a highly potent intervention that elicits important changes in a range of clinically relevant health outcomes in reproductive-aged women.

This study will investigate fetal responses to a single bout of HIT. Preliminary data of the investigators suggest that HIT does not negatively influence fetal heart rate. Others have reported that uterine and umbilical blood flow are not changed during or following acute exercise. However, no previous study has determined the acute effect of HIT on uterine blood flow and there are no studies investigating the fetal blood flow distribution in response to exercise. Since the relative distribution of blood to the fetal liver is associated with newborn adiposity, fetal blood flow distribution in response to exercise can provide insight about the effect of maternal exercise on offspring health.

Inclusion Criteria:

• pregnant, gestational week 22-36
• singleton fetus
• no known diseases
• capable of cycling on an ergometer bike

Exclusion Criteria:

• hypertension
• gestational diabetes mellitus
• any contraindication to exercise training