Vol. 19 Suppl. 4 2009 Reproductive BioMedicine Online; www.rbmonline.com/Article/4314 on web 10 September 2009 ©Published by Reproductive Healthcare Ltd., Duck End Farm, Dry Drayton, Cambridge CB23 8DB, UK Contribution from 11th World Congress on Controversies in Obstetrics, Gynecology and Infertility (COGI) 'Celebration - 30 years of IVF' and Serono Symposia International Foundation Luteal-phase endocrinology IE Messinis, CI Messini, K Dafopoulos Department of Obstetrics and Gynaecology, University of Thessalia, Medical School, 41110 Larissa, Greece Correspondence: e-mail: messinis@med.uth.gr Professor Ioannis E Messinis was trained in Obstetrics and Gynaecology in Athens and in Reproductive Endocrinology in Sweden. He has worked in Edinburgh and Aberdeen in the post of Senior Lecturer. Since 1995 he has been Professor in Obstetrics and Gynaecology at the University of Thessalia, Larissa, Greece and Head of the Department. His has two MD degrees and a PhD (Aberdeen) and has been author on 150 papers in peer-review journals and several chapters in books. He has served as an Associate Editor of Human Reproduction and a member of the Advisory and Executive Committees of ESHRE and currently of the Advisory Committee of MSRM. Abstract The corpus luteum is formed from the pre-ovulatory follicle under the action of the mid-cycle LH surge. LH is the main luteotrophic hormone in women controlling luteal structure and function during the normal menstrual cycle. Local factors, however, including progesterone are also involved. If conception does not take place, luteolysis occurs as a physiological apoptotic process. Human chorionic gonadotrophin, secreted after implantation, is able to rescue the corpus luteum and extend its lifespan. In ovulation-induction cycles, the negative feedback effect of the ovarian steroids on the pituitary is markedly potentiated, leading to the suppression of endogenous LH secretion during the whole menstrual cycle. The marked suppression of LH secretion disrupts corpus luteum function regardless of the treatment regimen. Summary for lay readers The corpus luteum is formed from the ovulated follicle under the influence of the endogenous LH surge. LH is the principal hormone that stimulates the production of progesterone and supports corpus luteum function in women. If conception fails, regression of corpus luteum takes place, a process named luteolysis. The causes of luteolysis in humans are not known. Nevertheless, the function of the corpus luteum is rescued when conception occurs by human chorionic gonadotrophin. In IVF programmes, ovarian stimulation leads to a marked suppression of LH secretion that disrupts corpus luteum function.