Danish researchers say road traffic noise may affect the reproductive health of couples trying to have a baby. According to a recent paper published in Environment International, every 10 decibels (Db) of extra traffic noise around a woman’s home increased the chance the pregnancy took six months or longer by 5 to 8 percent.

The findings were reported by a team led by Jeppe Schultz Christensen of the Danish Cancer Society Research Center in Copenhagen who combed through data on 65,000 women living in Denmark. The participants were involved in the Danish National Birth Cohort which ran between 1996 and 2002. Christensen and colleagues selected all the women who tried to get pregnant during the project that also had traffic noise data available for where they lived.

Previously, a German prospective study found 80 percent of women who are actively seeking to get pregnant do so within six menstrual cycles. Oddly enough, though, if a Danish women lived near a noisy road, her chances of getting pregnant in the six months fell sharply. This link withstood even when factors like poverty levels or nitrogen oxide pollution were taken into account.

However, this association did not seem to be statistically significant anymore for women who took more than 12 months to get pregnant, likely because other factors are affecting fertility in this case.

It’s unclear at this point why noisy traffic might affect women, or couples for that matter, trying to have a baby. It may be that case that noisy streets near a woman’s home cause sleep disturbance which was previously linked to decreased fertility in women but also low-quality semen in men. Constant racket can also activate a system in the brain known to disrupt ovulation. If this is a real causal relationship at stake, we should be worried because noisy traffic is so common in virtually every town and city in the world. Moreover, traffic noise is set to increase as more cars are added to the roads, especially in developing countries. More work is needed before we can assess how worrying this trend may be but in the meantime, couples looking to have a baby should choose bedrooms as far away from the road as possible.

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