Are bigger babies better?

He was big. He was beautiful. And he was hers. All 10 pounds, 13 ounces of him.

That’s how much Seamus Smyth weighed when he welcomed the world just over a year ago on February 3, 2005. He was Mary Griffin’s second child. “This guy just blew me away,” says the Victoria mom (five-foot-eight and 150 pounds), whose first son was a mere seven pounds, nine ounces.

Rachel Staples, a petite Victoria mom of three boys, can empathize. Elliot, her first, checked in at nine pounds, nine ounces. The second, Oliver, was 10 pounds, four ounces. And Isaac, the third, was…well, Staples’ anxiety mounted with each passing week of her pregnancy. Staples’ obstetrician had warned her that subsequent pregnancies tend to result in bigger babies.

“I was concerned,” Staples recalls. “All that was in my mind was ‘Is this going to be an 11-pound baby and what is that going to feel like?’” She describes her first two deliveries as “very difficult.”

As it happened, Isaac slipped out at an even eight pounds after two relatively easy hours of labour. Still, he was slightly bigger than the average Canadian baby, who tips the scales at just over 7½ pounds.

A big trend?
There’s no doubt about it — Canadian babies are getting bigger, as are babies in the US, UK, Australia, parts of Europe and elsewhere in the developed world.

An examination of Statistics Canada’s record of birth weights from 1970 to 2003 reveals that the proportion of male babies weighing four kilograms (eight pounds, 13 ounces) or more rose from 10 percent to nearly 16 percent. On average, boys weigh 100 grams (3½ ounces) more than girls at birth. The percentage of female babies in that same weight category nearly doubled during the same period.

Michael Kramer is a professor of paediatrics, epidemiology and biostatistics at McGill University. Kramer looked at birth weights of babies born at Montreal’s Royal Victoria Hospital from 1978 to 1996. His study, Why Are Babies Getting Bigger?, was published in the October 2002 Journal of Pediatrics. Kramer discovered that full-term babies were larger for their gestational age, while decreasing numbers were considered small for gestational age. On average, babies born at 37 weeks or more weighed 57 grams (two ounces) more than their counterparts 18 years earlier.

Although that may not sound like much, it is. Kramer points out that this increase happened over a period when the number of post-term deliveries went down and the number of preterm deliveries went up — both trends that should result in smaller babies. But despite those downward forces, “the mean birth weight has still gone up,” Kramer says.

The big question: Why?
In his study, Kramer examined mothers’ weight and height before pregnancy, weight gain during pregnancy, smoking habits, education levels, and incidence of gestational diabetes and high blood pressure.

What he found was both good and, in his words, “worrisome.” The good news is that far fewer Canadian women smoke during pregnancy, a change that has brought many health benefits, and bigger babies.

Says Kramer: “I would never suggest that women should smoke in order to keep their babies smaller.”

Now, the troubling news. Kramer’s study also documented a rise in gestational diabetes — a condition where the mother’s increased blood sugar circulates in the baby, leading to excessive growth and more fat. Women over age 35 are at greater risk for gestational diabetes and Canadian mothers keep pushing the age envelope, says Vyta Senikas, associate executive vice-president of the Society of Obstetricians and Gynaecologists of Canada. In 1991, about one-third of babies in Canada (excluding Ontario) were born to women aged 30 and over. Recently, that number jumped to 50 percent.

How much weight a mother gains during pregnancy may also affect her baby’s size. Nowadays, women put on more pounds than they did 20 years ago, Kramer says. The standard weight-gain recommendation during pregnancy is around 11 kilograms (25 pounds), but according to the US Centers for Disease Control and Prevention (CDC), one in five pregnant women gains 18 kilograms (40 pounds) or more.

Probably the key factor contributing to larger babies, however, is not a woman’s weight gain during pregnancy but her weight before. A mother’s size has far more effect on how big her baby will be than a father’s. That means small women tend to have smaller babies and large women tend to have larger babies, irrespective of the father’s size. Overall, says Kramer, Canadian mothers’ body mass index (BMI), a measure of weight to relative height, “has gone up a lot and shows no signs of slowing down.”

A big concern?
Yes and no.

No one is suggesting we should strive for underweight babies. But our idea of what looks healthy on a baby is coloured by hundreds of thousands of years of history when our ancestors lived as nomads, hunters and gatherers and subsistence farmers. “During that time, under-nutrition was a much bigger threat than over-nutrition,” Kramer explains. “Now we’re stuck with that image in an era when the risks are…more over-nutrition than under-nutrition.”

So, while babies need relatively more fat than kids or adolescents, they can have too much of a good thing. High birth weight can affect the rate of weight gain in childhood, and children who gain a lot of weight quickly are at greater risk of obesity, heart disease and diabetes later in life. The World Health Organization (WHO) recently reported that childhood obesity is at epidemic levels, affecting an estimated 17.6 million children worldwide.

“There’s no question that larger babies are more likely to be obese kids and, therefore, obese adults. That’s clear,” says Kramer.

However, big babies can present problems even before they are born. “The concern is always: Can I deliver this baby vaginally without any problems occurring?” says Senikas.

Understandably, very large babies — those five kilograms and up (more than 11 pounds) — have more delivery complications and an increased risk of birth injuries. But not always. Senikas says there’s a crucial difference between “a long, proportionally big” baby and a “fat, pudgy” baby. For instance, the biggest baby she ever delivered was 6.6 kilograms (14 pounds, eight ounces). “But the mother was six-foot-two and 190 pounds pre-pregnancy, and the father was six-foot-seven and 200-something pounds, and this was a perfectly average baby for the two of them.”

The WHO is addressing the baby growth rate issue next month with the release of new growth charts outlining optimal growth rates based on a seven-year study of babies who are breastfed and born to non-smoking moms (current charts are based on formula-fed babies). Preliminary reports suggest these weights will be significantly lower than current guidelines — but keep in mind that, like all growth charts, they will be a tool for tracking development, not a rule book.

Kramer does not expect children’s sizes will change in response to the new WHO charts. But are bigger babies doomed to a future of fat and illness?

Far from it, Kramer says. A high rate of weight gain is nothing to worry about in a baby’s first year of life. And although “a fat baby has a higher likelihood of becoming obese, most overweight babies will not be overweight adults.”

Whether babies are breastfed or bottle-fed, according to Kramer it’s what happens after weaning that really matters.

That’s positive news for parents. It means they have the power to determine their children’s future health by offering healthy food choices and encouraging kids to be active.