Fertility treatment is more likely to be successful in the summer months, researchers have found.
The team from Liverpool and Chester said the trend was probably linked to the same biological process that means other mammals give birth in spring.
They told the British Fertility Society Conference the women needed far fewer drugs to help them ovulate during months with more daylight.
The rate of successful pregnancies was also higher after summer treatment.
It has been observed that there is a seasonal variation, but it has been thought it might be linked to warmer temperatures in summer months.