The Influence of Extended Daylight on Outcomes of IVF/ICSI Cycles

Abstract

The influence of seasonality and daylight length on mammalian reproduction has been well established. From analysis of historical birth records of countries at increased latitudes, prior to the widespread availability of family planning, there has existed a seasonal bias in human reproduction with an increase in conceptions occurring during the summer months leading to spring births. This process is known as photoperiodism and appears to be under the control of the hormone melatonin. In Assisted Reproduction cycles there is much greater uncertainty as to the effect of seasonality, with some suggestions that in countries of higher latitudes daylight length may influence outcomes. We wished to confirm if this seasonal variation exists, and to what effect daylight plays on outcomes in IVF/ICSI cycles. This was a retrospective analysis. This was a 4-year retrospective analysis of 3568 cycles of IVF/ICSI performed at a single tertiary University Assisted Conception Unit between December 1997 and Nov 2001. From these 2709 cycles were isolated that used a standard long protocol regimen for pituitary desensitisation and ovarian stimulation with Human menopausal gonadotrophin (HMG). Data was collected with regard to the demographics of the patients undergoing treatment as well as the outcomes including, quantity of gonadotrophin utilised, oocytes retrieved, fertilisation, implantation and clinical pregnancy rates. To remove bias from this retrospective study we identified 266 patients who had undergone two cycles of assisted conception cycles, one performed during the summer months (April- September) and one during winter months (October-March). These patients acted as their own controls between the two cycles and matched data was then compared. Analysis of these 532 cycles in 266 patients showed that in 131 patients the first cycle was performed during the summer and in 135 patients the first cycle was performed in winter. When the data from the matched cycles were analysed the significant improvements seen in outcomes from cycles performed during summer months was confirmed. Cycles undertaken during summer months showed significantly less gonadotrophin was required for each oocyte retrieved 734 iu v 849 iu (p=0.003), as well as a significant improvement in implantation rates per embryo transferred 8.86 v 4.46 (p=0.016) and clinical pregnancy rate 15.7% (42/266) v 7.5%(20/266) (p=0.002). Increasing daylight had no effect on fertilisation rates seen in IVF cycles 50.3% v 50.0%. The results of this study appear to demonstrate the benefit of increased daylight length on outcomes of IVF/ICSI cycles. It is known that the anatomical and molecular substrates and receptors of the system that encodes changes in photoperiodism are preserved in humans and that this system appears intact from the retina to the cortex, pineal gland and hypothalamus. In animal studies melatonin receptors have been found in many different anatomical sites, including the ovary. It would therefore seem probable that melatonin may have actions at multiple sites and on multiple levels of the reproductive tract, and may exert a more profound effect either alone or through hormone cascades on outcomes of assisted conception cycles than has been previously considered. Further research is required to confirm these findings and to identify the possible mechanism of action for the effect of extended daylight on reproduction.