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Twin peaks

What’s behind the seeming abundance of twins born in the Sea to Sky?

When my husband and I found out we were pregnant with twins, we were shocked. They didn’t run in my family and we weren’t doing any fertility treatments that might have increased our chances of twins, but there they were, two little blobs on the ultrasound printout. A few scans later and we found out they shared a placenta, which about 70 per cent of identical twins do, known as monochorionic twins. We also learned they were identical twins, which don’t typically run in families the same way fraternal twins do. 

As my belly grew, and grew, and grew, the more I talked to friends, neighbours and complete strangers about my pregnancy and how I’d got two-for-one baking in the oven. And that’s when I heard it, the bit of local hearsay that inspired this article. What I heard went something like this: “You’re having twins? Did you know that the Sea to Sky corridor has one of the highest rates of twins in North America along with a small potato-farming town in the States?” If only one person had mentioned it to me, I would have likely forgotten about it, but I heard it over and over from different people. Then, last summer, I got into my friend’s truck with three other women to go for a bike ride and one of them commented how crazy it was that not only were all four of us mothers of twins, but we all live in the same neighbourhood—three of us even on the same street! What were the odds?

When I started researching this article, I reached out to the Sea to Sky Multiples group on Facebook (yes, it’s a thing) and a lot of them had heard almost exactly the same hearsay I had. I was not alone (or crazy). 

“I have 20-month-old identical twins and I have been told this many times by random people at Strong Start (Sea to Sky Community Services program) and at the park.” Sarah Ewing, identical twin girls, Squamish. 

“I have heard that. I actually blamed the carrots after hearing this because I was eating a lot of Pemby carrots when I got pregnant—same soil!” Jasmine Robinson, fraternal twin boys, Whistler.

“When I was pregnant with my twins, nearly 10 years ago, my OBGYN in North Van said something about a study, but I never asked for specifics.” Anon, Squamish. 

“I actually have heard that, but I don’t know where. Someone also once said there were studies done in the area or they were going to do studies on the high number of twins in the area. I’m not sure how true it is though!” Jen Bang, fraternal twin girls, Whistler. 

So, does this hearsay have any truth to it? Do we have a high number of twins in the Sea to Sky? If so, why? Can potatoes actually play any role in it? As it turns out, these questions don’t have simple answers. 

“You’re going to need to ask some detailed questions to really understand this,” explained Dr. Marina Tourlakis, life sciences tutor in molecular genetics at Squamish’s Quest University, in an email. “Fraternal, or non-identical twins, can result from fertility treatment, which often induces the release of more than one egg during a woman’s menstrual cycle (super-ovulation). Fertility issues are prevalent in our society … and hence increased twinning rates, if non-identical, might be explained by increased awareness of, and accessibility to, fertility treatments. Hence, I’d wonder if the proposed high rates of twinning in Whistler are of identical or fraternal twins as these are two very different questions to ask. 

“If the average age of the mothers in Whistler is high, and we are talking about fraternal twins, then I’d wonder if this is indeed linked to an increase in fertility treatment (since fertility drops precipitously with age). Given that fertility treatments are expensive and Whistler is typically associated with an affluent demographic, this too would make me wonder if this is the main factor at play.”

Statistics Canada helped me compare the number of twins born in the Sea to Sky to the rest of Canada between 2000 and 2020. For 12 out of those 20 years, Squamish, Whistler and Pemberton’s combined twin percentage rate was higher than the Canadian average. For six straight years spanning 2012 to 2017, the corridor remained above the national average. It’s worth noting, however, that the mean average of those years puts the twinning rate at 3.1 per cent, in line with the rest of Canada, while a median average puts us at 3.3 per cent, just over. 

Statistics Canada does not collect information on whether twins are identical or fraternal, or if they were conceived using fertility treatments, but for 60 per cent of that 20-year period, we’ve had more twins than the national average, so the hearsay about the Sea to Sky having an above-average amount of twins could be somewhat true, although the reasons why are an educated guess without more robust data. 

What Tourlakis was saying about fertility treatment being the major driver in increased fraternal twin rates is echoed in a comprehensive, global study led by Christiaan Monden, a professor of sociology and demography at Oxford University. The research shows that over 40 years, the twinning rate worldwide has increased by a third, which means that one in every 42 babies is now born a twin. 

“Our results show that twinning rates were recently peaking at a historical high, with rates of over 15 twin deliveries per 1,000 deliveries in many countries, including the USA, Canada, the European Union, Israel, South Korea, Taiwan, and almost all African countries,” the study says. 

The report goes on to say the reasons for the increase are driven by fertility treatments (responsible for two-thirds of the increase) in combination with households delaying childbearing, in other words, older mothers (responsible for one-third of the increase). 

An international collaboration (2020) involving researchers at The University of Western Australia (UWA), DePauw University in Indiana and the London School of Hygiene and Tropical Medicine found that women are more likely to conceive fraternal twins once they reach their 30s as a result of an evolutionary response to combat declining embryo viability. 

“This research offers important insights into how our evolutionary past still influences our modern lives, with fraternal twinning rates increasing as women increasingly delay childbearing,” said Associate Professor Joseph Tomkins, UWA School of Biological Sciences.

Note that this research refers to fraternal twins specifically, as the reason an egg “randomly” splits to create identical twins is still a mystery. However, new research into epigenetics might be the start of unravelling this biological enigma.

“Epigenetics refers to the turning on and turning off of genes,” explains Dr. Nancy L. Segal, a professor of psychology, director of the Twin Studies Center at California State University, Fullerton and author of seven books on twins, speaking on the podcast, Speaking of Psychology: What Studying Twins Can Teach Us About Ourselves. “What environmental triggers are there before birth and sometime after birth, that will activate a gene or perhaps silence it. And this is where identical twins, who differ in fundamental ways, may be of greatest use to us in the medical sciences because we know that the similarity rate of identical twins with diabetes or multiple sclerosis is only 50 per cent, schizophrenia maybe 40 per cent, so, if they come out into the world with the same genes, why is it that one twin expresses it and the other one does not? This is information we can all use to assist individuals in the non-twin population.”

Are Sea to Sky mothers older than the Canadian average? 

A 2019 CBC article stated that B.C. has the highest number of older mothers in Canada, with the average age of first-time mothers being 31.6 compared to the national average of 29.2. It went on to say that in B.C., between 2000 and 2017, the number of mothers aged 35 to 39 increased by 60 per cent, and the number of mothers aged 40 to 44 doubled. 

Statistics Canada helped me dig into the Sea to Sky numbers and in 2020, the average age of a mother in the corridor was 33.5, so above both the national average (31.3) and the B.C. average (32.1). Of the children born to mothers in the corridor, 78 per cent were born to mothers aged 30 to 39. In 2000, that figure was just 54 per cent. UBC professor Paul Kershaw, founder of research and advocacy group Generation Squeeze, is quoted in the CBC article saying the numbers didn’t come as a surprise. “This is the province where hard work pays off the least for younger people in their prime childbearing years,” Kershaw said. 

Kershaw’s research compared today’s young adults to those of a generation ago and found that the full-time incomes of British Columbians have dropped the most in Canada during that time while housing prices have increased the most.

The nature of work, housing, and the propensity towards play in the Sea to Sky could be a factor in people deciding to wait longer to start a family. The result? More issues conceiving, possibly fewer kids, but also a slightly higher chance, biologically speaking, of these women producing twins. Interestingly, while older mothers might have issues getting pregnant, they are statistically more likely to have a successful multiple pregnancy if one does occur, said researchers at Columbia University Irving Medical Center in a 2017 study.

Tater tots: Are Pemberton's potatoes really a factor? 

A U.S. study by the National Center for Health Statistics spanning from 1980 to 2009 showed that the national twin birth rate rose an incredible 76 per cent over that period, from 18.9 to 33.3 per 1,000 births. Increases were seen across all 50 states and by more than 100 per cent in five states—Connecticut, Hawaii, Massachusetts, New Jersey, and Rhode Island. 

The report notes that Connecticut had the highest number of twin births at five per cent in 2009. More recent figures published by Statista in May 2021 also show Connecticut as the state with the highest twin birth rate from 2017-19.

While it is known for its stunning fall foliage, Yale University and being the home of ESPN, Connecticut is not exactly known for potatoes. So, the Sea to Sky’s connection to a small, potato farming town in the U.S.? Still possible, but again, without more data, it’s difficult to say for sure. (The U.S. CDC was unable to narrow down where this mythical potato town with the high twinning rate is located.) Seed potatoes have been farmed in Pemberton for more than a century, so wouldn’t the numbers of twins stay consistently high or spike when we had bumper crops? What a woman eats and drinks have not been scientifically linked to the subsequent production of twins, although some people think it could be. 

Anna Capria, a human genetics and genomic data analytics masters’ student, led me to an article on a small Nigerian town called Igbo-Ora. Nigeria has one of the largest populations of twins in the world and the highest dizygotic/fraternal twinning rate (45 per 1,000). A recent 2020 study delved into the local people’s beliefs as to why this might be, and mentioned a soup produced with okra leaves and a local delicacy made from cassava, a root vegetable.

“Since the same foods are consumed in neighbouring communities that have lower rates of twinning, we conjecture that nutritional and other environmental factors may produce epigenetic modifications that influence high DZ twinning rates in Igbo-Ora community. We conclude that more directed scientific studies based on these findings are required to further elucidate the etiology of the high rate of DZ twinning in Igbo-Ora,” the study says.

My post on the Sea to Sky Multiples group helped to unearth other twin-heavy places in Brazil and India. In an article about Kodinh, a small village in India that counts more than 400 sets of twins, it was interesting to read that some of the pervasive reasoning for multiple births, like more mature mothers and access to fertility treatments, are not a factor there. The doctor interviewed mentioned that he thinks it’s something in the food or water in the area, but again, there’s no concrete evidence. 

One long-held twin myth that has recently been busted is the notion that identical twins don’t run in families. “We thought that for a very long time,” says Segal. “And yet, some recent research from Sweden and Singapore looking at inbred populations has found that there are these pockets of people around the world in India and Iran, where there are multi-generations of identical twins. And so, we think that within some families that there’s a tendency towards zygotic splitting.” 

In the podcast, Segal goes on to explain that the offspring of two pairs of identical twins would be first-cousins and full siblings, because each parent is genetically interchangeable, which is rare—but a trend that’s not so rare is identical twins marrying unrelated people, and that their children would be genetic half-siblings. Mind-blowing.

Sea to Sky hearsay

What’s become clear over the course of digging into this hearsay is that there is a serious lack of comprehensive research on twins, part of a longer trend in academia that tends to skew towards a male perspective. 

“Female reproduction has a long tradition of being studied primarily from a male lens (because researchers and medical doctors were primarily male) and poorly at that (perhaps because the funding bodies deciding what research to fund were also primarily male),” says Tourlakis. “Recently there has been a surge in attention (perhaps due to an aging mother population, and perhaps also due to increased numbers of women in research positions) to reproductive studies, which is leading to all kinds of interesting new findings about fertility, so I imagine we will continue to have exciting new findings hitting our science news feeds in the coming years.”

So, one day we might be able to debunk or uphold this strange bit of Sea to Sky hearsay, but for now, it’s still a bit of a mystery. 

“Being the mother of twins in the Sea to Sky area these days may seem commonplace, but it doesn’t take away from how incredibly special it is to have them.” Sarah Lindsay, identical twin boys, Squamish. 

Writer’s Note: Thank you to Dr. Marina Tourlakis and Anna Capria for explaining genetics basics and to David Raffo for patiently helping me draw some answers from the data.