Personal trainer Melinda Nicci says:

'The first trimester is not the time to start exercising vigorously. It should feel comfortable, rather than working to exhaustion.
'If you can have a conversation while power-walking or doing aerobic activity, you're working at a safe level. However, if you're huffing and puffing and can't talk, then you're overdoing it.
'You can expect to have a bit of aching in your calf or thigh muscles, but you should stop if you have a sharp shooting pain.'