Endometriosis is a common gynaecological condition with an estimated prevalence of 200 million worldwide[1]. It affects 1 in 9 individuals assigned female at birth and is the most common cause of chronic pelvic pain. The natural history of endometriosis is unknown and whether the disease is progressive remains controversial in medical literature[2]. Due to the scarcity of studies in this area, there is no official consensus or definition to describe disease progression in endometriosis[2]. However, literature has shown that transvaginal ultrasound is useful in detecting DIE [3]. Previous studies exploring progression of endometriosis found a low risk of progression but were limited to bowel endometriosis[4]. Koninckx et al. reported that the incidence and depth of typical endometriosis lesions increased with age, whereas subtle lesions decreased with age[5].

The COVID-19 pandemic that began in early 2020 resulted in a significant reduction in elective operations in Australia, including endometriosis surgery[6,7]. This resulted in women with stage III and IV endometriosis having delayed surgical management. During this time, patients with deep infiltrating endometriosis received surveillance ultrasounds up to 12 months apart until operating recommenced. This presented an opportunity to study the natural progression of endometriosis. A study investigating the sonographic progression of endometriosis would be beneficial to current literature and aids in guiding timely surgical management. This study hence aimed to investigate the progression of deep infiltrating endometriosis using transvaginal ultrasound surveillance of patients undergoing non-surgical management.