Just mentioned this to DP and he said he's heard it's hard for cyclists to have kids in general? But I guess as Em says it's not a rule.

I have heard though that men who are stressed are more likely to produce sperm with X-chromosomes and so are more likely to have all-girl families. Men who manage their stress better apparently are more likely to have all-boy families.

Apparently this was the result of a medical study; thinking of the men I know who have all girl families and all boy families, the stress-heads definitely had the girls!