File photo: Previous research has found traffic noise could delay ovulation in women, while the stress and sleep disruption it brings may affect men’s sperm quality. Picture: AP

Couples living near busy roads may find it harder to get pregnant because of the stress of traffic noise, according to researchers.

Women exposed to noisy roads are more likely to take six to 12 months to fall pregnant. Their chances of that delay rise eight percent for every 10-decibel increase in the volume of traffic, an analysis of more than 65 000 women found.

Previous research has found traffic noise could delay ovulation in women, while the stress and sleep disruption it brings may affect men’s sperm quality.

The study, published in the journal Environment International, follows research showing that living close to busy roads raises the risk of pregnant women suffering serious complications.

The authors, led by Jeppe Schultz Christensen at the Danish Cancer Society Research Centre in Copenhagen, said: "Traffic noise induces sleep disturbance and stress. Sleep disturbances and stress may affect the fecundity (time to pregnancy)."

Couples who live near noisy roads have raised levels of the stress hormone cortisol which is believed to activate a particular area of the brain, known as the hypothalamus-pituitary-adrenal axis.

The activation of this area is thought to make conception more difficult, with previous research showing it can alter blood flow in the fallopian tubes.

The change to the brain from traffic noise may also delay a hormone surge which triggers ovulation and affects sperm production in men.

Professor Adam Balen, of the British Fertility Society, said: "The study is small and shows only a small effect. There is no evidence of a cause for the effect seen, which would be critical if it is to inform patients and doctors about potential causes of infertility."