When it comes to considering fertility treatment, scientists say that women who have the treatment during the summer are twice as likely to become pregnant as those who have it in the winter.
Apparently patients who had two cycles of in vitro fertilization, one during months with more daylight and the other during darker periods of the year, had substantially more chance of conceiving as a result of their treatment between April and September.
Researchers say that while it is not yet fully clear why this happens, they believe melatonin, a hormone secreted in the pineal gland in the brain in response to darkness, plays an important role.
From an evolutionary standpoint, giving birth during the spring or early summer may make sense, because previously those born during the coldest months, when less food was available would have had less chance of surviving.
The team of researchers, from Chester and Liverpool, in the UK, also found that those who had IVF cycles during months with the most daylight needed lower doses of drugs to stimulate ovulation.
However, the scientists do warn women whose chances of having a baby are falling because of age, that they should not delay treatment until the summer, because any improved chance of pregnancy due to extra sunlight is likely to be offset by age-related decline in fertility.
Simon Wood, from the Countess of Chester Hospital, who led the study, says the results of the study appear to demonstrate the benefit of increased daylight length on outcomes of IVF cycles, and it seems probable that melatonin may have a more profound effect on outcomes of assisted conception cycles than has previously been considered.
In the study Dr Wood and colleagues at his hospital and others at Liverpool Women's Hospital, analyzed the outcomes of fertility treatment carried out on 266 women who had had two cycles, one performed during April to September and the other between October and March.
Of these, 131 patients had their first cycles during the months with more daylight, and 135 had treatment during the darker half of the year.
At 42 out of 266, or 15.7 per cent, the pregnancy rate for cycles during the summer was double that during winter - 20 out of 266, or 7.5 per cent.