Midwife Katie replies:

This is an internal examination, where the midwife or the doctor slides an index finger through the opening of the cervix, the neck of the womb, and around its inner surface. This effectively ‘sweeps' the cervix away from the membranes covering the baby's head and stimulates the production of hormones called prostaglandins that trigger labour.
Studies have shown that membrane sweeping doubles the rate of spontaneous labour in women at term compared to situations where no action is taken. It doesn't have any serious side effects and it reduces the need for more complicated induction methods, so it's often suggested before anything else.
The only downside is that it can be quite uncomfortable, especially if your cervix is pointing backwards and is difficult for the midwife to reach. It may also cause some bleeding although it's not usually heavy. But momentary discomfort is worth it if it means you can go on to have a natural labour without any intervention.