When you summon forth the babies.
The mysteries of human evolution abound, but one thing I can say with some certainty is that when couples are happy, they often bone. One thing that occasionally makes people happy is sports. So, by the transitive property, we can conclude that happy sports things lead to happy people boning.
This, indeed, may have been the case in Iceland nine months ago, when the country's soccer team beat England 2-1 in the Euros. Now, as nature has taken its course and contraceptives have not, there is apparently a baby boom in Iceland, as reported by the Independent, via Icelandic newspaper Visir. If you listen to the Icelandic booth in the moments after the final whistle, it's possible they started right then and there.
Now, all of this is based only on a single tweet from a doctor working in the maternity wing of Iceland's biggest hospital. He didn't provide any numbers to back up his claim, the tweet merely reads (via Google Translate) that the hospital "set a record for the number of epidurals in the maternity duty this weekend," which happened to be nine months after the England game.
hehehe dagsins:— Ásgeir Pétur (@asgeirpetur) March 27, 2017
sett var met í fjölda mænudeyfinga á fæðingarvakt um helgina - níu mánuðum eftir 2-1 sigurinn á Englandi
In case you've forgotten from the wall-to-wall coverage of Iceland during the Euros, the country has only 300,000 people, so it shouldn't take much celebratory screwing to set a births record.
Regardless, this is hardly the first time happy sports fans have produced happy sports families. There was a baby boom in Barcelona after the club won a bunch of things in May 2009, in New Zealand after a big rugby win in 2011, and possibly Boston after their first World Series win since 1918 (although that story is mostly anecdotal evidence). Interestingly, one of the couples the Globe interviewed didn't bang nasties because they were happy. They were in New York at the time and wanted to go to sleep, but the partying from the Irish bars on their block was so loud they ended up making sex instead. Now that's a romantic tale I can relate to.