Complex sentence: Prior to 2015, the women's race, which first took place in 1927, was usually held at the Henley Boat Races along the course; on at least two occasions in the interwar period, the women competed on the Thames between Chiswick and Kew.
Split into simpler sentences: Prior to 2015, the women's race which first took place in 1927, was usually held at the Henley Boat Races along the course. However, on at least two occasions in the interwar period, the women competed on the Thames between Chiswick and Kew.