Yes. It is important to inform your teacher of your condition prior to the class so that they can modify the asanas (poses) to suit your condition. Iyengar Yoga is a therapeutic yoga system and your practice can be modified in class to assist and work appropriately with your condition.
It is important to inform your teacher if you are menstruating. There are specific yoga poses that are beneficial to the body and mind during this time. A menstrual practice includes combination of restful postures that may ease pain, fatigue and strain. For more information download Geeta Iyengar’s The practice of yoga during the whole month.
Regular attendance to class is encouraged to get the most benefit from class This also encourages consistency in the class. Attending once a week, you will observe benefits. Attend two classes/weekly and you will see and experience benefits and changes to your body and mind more quickly.