Illustration highlighting the role of insulin in augmenting luteinising hormone (LH)-dependent thecal androgen (A) synthesis, and the reduction in that synthesis if hyperinsulinaemia improves. Illustration highlighting the role of insulin in augmenting luteinising hormone (LH)-dependent thecal androgen (A) synthesis, and the reduction in that synthesis if hyperinsulinaemia improves. Follicle-stimulating hormone (FSH)-driven estradiol (E) synthesis continues. See text for an explanation of stages a–f. W Colin Duncan J Fam Plann Reprod Health Care 2014;40:217-225 Copyright © by the BMJ Publishing Group Ltd & the Faculty of Sexual & Reproductive Healthcare of the Royal College of Obstetricians & Gynaecologists. All rights reserved.