I have discussed your question with a dietician. She said that it is safe to assume that brand-name yoghurts (and other dairy produce) sold in mainstream shops are made from pasteurised milk. As with most foods, we have to trust that the product was then prepared in a hygienic manner that minimised the risk of subsequent contamination with germs.
Dairy foods – yoghurts, cheese and so on – that are made from unpasteurised milk are generally clearly labelled as such. Some products – perhaps home or farm-made – may not be clearly labelled, and may be best avoided unless you are sure of the origins.
Yoghurt is an excellent source of calcium, and therefore a useful addition to your diet (especially if you don’t like liquid milk). Eating live yoghurt may also help restore the balance of healthy bacteria that live normally in the bowel after this has been upset by a course of antibiotics or hormonal changes. Once the balance is restored, the organisms that cause thrush are less likely to multiply and cause the usual symptoms of itching, soreness, and discharge.
Although eating live yoghurt may help prevent attacks of candida (or thrush), an active infection may need more specific treatment. Ask your midwife, doctor or pharmacist for advice.