Many Canadian couples take more away from the holidays than happy memories, data shows.

Birth records from four provinces shows an apparent peak in conceptions in the last three weeks of December and the beginning of January.

The December pattern corresponds to a peak in births in mid-to-late September, a pattern seen consistently in British Columbia, Alberta, Ontario and Nova Scotia over multiple years.

Average daily births in the last three weeks of September were 9.2 per cent above average in Ontario, 6.5 per cent above average in B.C., 10.3 per cent above average in Alberta and 14.2 per cent above average in Nova Scotia.

“It’s a subtle pattern, and it’s probably a subtle pattern because we have so many other ways of controlling ferility right now,” explains Dr. Jennifer Blake, chief of obstetrics and gynaecology at Sunnybrook Health Sciences Centre.

Story continues below advertisement

Story continues below graphic

“But we do see this, and there is speculation. We see this in the animal kingdom: seasonal variation in when young are born. There are questions around whether it’s because of melatonin (a chemical affected by light), whether there’s something that we’re still light-sensitive about that’s affecting our fertility or whether it’s the Christmas season, and people are in a partying mood.”

All four provinces showed a dip in apparent conceptions in late February or early March.

“How much of this is behaviour and how much is biology, we really don’t know, but we do know that it’s a phenomenon,” Blake says. “It’s been well-described and well-reported. You have to ask: Are there any survival advantages to having your young born in the fall months? You would have thought that that that’s a time when you wouldn’t want young to be brought into the world. Maybe it’s better, with the dark months and the quiet time? It’s an interesting question.”

Story continues below advertisement

Data was based on birth date records supplied by the four provinces. Global News worked with three years of data for Ontario, one for B.C., two for Alberta and six for Nova Scotia.

In a separate pattern, births on or around Christmas Day itself were well below average in all four provinces. This seems to account for the dip in the graphs seen in late April.

Seasonal changes in birth rates have been studied since at least the early nineteenth century. Explanations offered have included sunlight, available nutrition, the month of the mother’s own birth, available time for sexual activity and many other factors.

Birth data for four provinces, backdated by 40 weeks, show roughly the same pattern. Ontario’s data is from 2007-9, B.C.’s from 2010, Alberta’s from 2009 and 2010 and Nova Scotia’s from 2005 through 2010.

READ MORE: Quebec birthrate falls for sixth straight year

Story continues below advertisement