When LH is higher than the maximum threshold, LH receptors are downregulated, which inhibits granulosa cell proliferation and leads to premature oocyte luteinisation and follicular atresia.[42,43] Studies showed that 1.2 U/L ≤ LH ≤ 5 U/L is the ‘threshold window’ for follicular development and oocyte maturation.[44] For patients with PCOS, whether the ‘LH window’ is the same as that of the normal ovarian responders and whether the threshold window is enlarged or narrowed need further research and discussion. This evidence concerns the gene PLOD1 and polycystic ovary syndrome.