A study has found that women undergoing IVF are most likely to conceive in the warmest months, and least likely in autumn and winter.
Researchers in Israel analysed more than 4000 in vitro fertilisation cycles and linked them to pregnancy rates among patients.
In autumn, 29 per cent of the patients became pregnant compared to 30 per cent in winter and 31 per cent in spring.
In summer, the pregnancy rate rose to 37 per cent. The highest pregnancy rate was seen in early summer, when 44 per cent of patients undergoing IVF became pregnant.
It is not known why the success rate differs between seasons.
But Dr Simon Fischel, director of the CARE fertility clinic in Nottingham, England, suggested the link may be the effects of increased light during the summer months on the glands responsible for a woman's cycle.
He said: "Animal studies have shown that increasing amounts of light make conception more likely because it results in a more highly regulated cycle.
"There is probably a vestigial role remaining in human reproduction between the pineal gland and levels of natural light."
But women having fertility treatment were usually given hormones which suppressed their natural cycles.
Dr Fischel suggested: "It may be that the interaction between the brain and the gland continues on some level in order to facilitate treatment."
Another reason could be evolutionary. If a woman becomes pregnant in the summer, she will give birth in the spring, meaning her baby's first months of life are during the warmer and less risky summer months.
- INDEPENDENT
Herald Feature: Health
Related links
Summer best time for fertility treatment
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