1 Use moderate intensity, which is sufficient to improve cardiovascular fitness, muscle strenght and flexibility. 2  Perform exercises regularly: cardiovascular exercise: 3 to 5 times per week, strenght training: 2 to 3 times per week.
The pregnancy starts from the first day of her last menstrual period. Normally 2 weeks before ovulation. An ultrasound is the most accurate way to determine pregnancy dates. So yes, she can be 6 weeks and 3 days pregnant even though you only met 5 weeks ago because two of those weeks were before conception.
1 Calculating the gestational age from the conception date is more accurate. It is the preferred way of the medical textbooks.  How far along you are in your pregnancy (from the first day of the last menstrual cycle) Calculating the gestational age from the from the first day of the last menstrual cycle is more practical.