• Normal ovary obscured by gas more common on the left side due to sigmoid gas

• Bladder over/underdistended

• Previous oophorectomy

• Displaced — anteversioretroversion, uterine masses, leiomyoma

• Ectopic ovary — in inguinal canal, failure of descent, low ovary

• Children (commonly seen by modern scanner)

• Postmenopausal — small ovaries

• Atrophic ovaries

• Small ovaries — e.g. Turner’s syndrome

• Müllerian dysgenesis

• Distorted pelvic anatomy — previous surgery, previous radiotherapy.