There are a lot of stories and old wives’ tales surrounding pregnancy and birth, and each and every possible factor of having a baby is subject of discussion. The potential size of your baby is no different, and whether or not you’ll have a large baby is a question on many people’s lips. Thanks to recent research though, that question can now be answered – at least for some people. Studies show that mothers who are overweight or obese during pregnancy are much more likely to have big babies than smaller mothers.

A recent co-operative review study between universities in the UK looked at research involving more than 30,000 women of European ancestry and their babies. The studies examined the mother’s body mass index (BMI), blood sugar levels, and blood pressure as well as the weight of the resulting babies. The results, published in the Journal of American Medical Association, demonstrated that not only will larger moms have larger babies, but moms with high blood sugar levels (whether overweight or not) will also have bigger babies. Conversely, moms with high blood pressure will have smaller babies [1] .

Big Babies

The size of the average baby is around 6-7 pounds [2] , but the amount of babies being born at 9.9 pounds or more has increased over the last ten years [3] . These are known as LGA babies, or ‘large for gestational age’. The American Journal of Obstetrics and Gynecology suggests that overweight moms are twice as likely to have an LGA baby and obese moms are three times as likely. What’s more, a study by the Kaiser Permanente Center for Health Research shows that women who gain 40 pounds or more actually during the pregnancy are also twice as likely to have LGA babies [4] , even if they started out with a healthy BMI. So the statistics show that this increase in baby size is there, but the questions we’re left with are why are babies getting bigger? And why does it matter?

Bigger Babies

The fact that babies are getting bigger is not only due to the size of the mother, of course. One of the most obvious reasons that babies are getting bigger is that we are getting healthier in terms of pregnancy development. Mothers generally don’t smoke and drink during pregnancy any longer, for example, and these factors influence the resulting size of the baby. That however would only explain a small growth, rather than why babies are increasingly being born LGA.

There are reasons though. One of the biggest causes of LGA babies is gestational diabetes, a form of diabetes that affects women during pregnancy alone. What’s interesting is that obese women are three times as likely to develop gestational diabetes during their pregnancy [5] , which could explain why bigger women are more likely to have bigger babies. Dr. Mark Dykowski, an OB/GYN at Generations OB/GYN Center in Michigan explains this, saying that “simply stated, glucose is the baby’s favorite fuel for growth. When maternal blood sugar is high, more glucose is available to the fetus, resulting in larger fetal weights” [6] .

The Detriment of Big Babies

But does it really matter whether babies are bigger? The answer, unfortunately, is yes. Other than the natural panic that a prospective mother may feel at the idea of having an overly large baby, the size of the newborn will have an effect on that baby’s health and well-being. Dr. Kristin Atkins, a specialist in maternal and fetal medicine at the University of Maryland says that “bigger is not always better when it comes to babies’ birth weights” [7] .

At the very least, larger babies can cause complications during childbirth. A common problem with larger babies is what is known as shoulder dystocia, where the shoulders of the baby get stuck in the birthing canal. This can cause damage to the collarbones and arms of the baby, and potentially result in nerve damage in their necks. For the most part, these issues sort themselves out after birth but in some cases, there can be lasting damage.

Other problems that large babies face are breathing difficulties, abnormally thick heart muscles, low blood sugar levels, and an increased risk of jaundice [8] . Dr. Rachel Freathy of Exeter University explains that a being born large can have just as big an impact as being born too small, and birth rates that are at the extreme ends of the spectrum are “associated with diseases such as type 2 diabetes later in life” [9] .

Grown-Up Big Babies

Being an LGA baby can affect children in later life too, and some doctors suggest it can play a role even into adulthood. Dagni Royasingam, a consultant obstetrician in the UK explains that “babies who are born bigger have a higher risk themselves of being obese, developing diabetes, and heart problems” [10] . Furthermore, a study review published in the British Medical Journal claims that big babies have an increased risk of being overweight in later childhood and beyond as adults [11] .

Of course, it’s important to remember that none of this means that your baby should be tiny. In fact, fat plays an important role when it comes to brain development, and babies naturally have more body fat that adults [12] , so new parents needn’t worry too much about their child’s weight. That said, if you want to reduce your chances of having an LGA baby, watch your weight gain both before and during pregnancy, exercise regularly, eat a healthy diet, and most importantly, speak to your physician about your concerns.

[1] Cited by Press Association, 2016, Overweight mothers have larger babies, research suggests, available at: http://www.theguardian.com/lifeandstyle/2016/mar/15/overweight-mothers-obese-pregnancy-larger-babies-blood-sugar-high-blood-pressure-smaller [accessed 04.19.2016]

[2] Your Plus Size Pregnancy, 2015, Your Child’s Risks for Being Overweight, available at: http://yourplussizepregnancy.com/parenting/children-overweight/#top [accessed 04.19.2016]

[3] Jen Meuller, 2016, Overweight Moms Have Larger Babies, available at: http://www.sparkpeople.com/resource/pregnancy_articles.asp?id=698 [accessed 04.19.2016]

[4] Ibid.

[5] Rachael Rettner, 2011, Big Babies: Are Heavy Newborns Healthy? Available at: http://www.livescience.com/35771-big-baby-health-risks.html [accessed 04.19.2016]

[6] Your Plus Size Pregnancy, op. cit.

[7] Rachael Rettner, op. cit.

[8] Ibid.

[9] Press Association, op. cit.

[10] Zoe Williams, 2013, Why big is not always beautiful when it comes to babies, Available at: http://www.theguardian.com/lifeandstyle/2013/aug/09/why-big-not-always-beautiful-babies [accessed 04.19.2016]

[11] Salynn Boyles, 2005, Do Bigger Babies Become Fatter Adults? Available at: http://www.webmd.com/parenting/baby/news/20051013/do-bigger-babies-become-fatter-adults [accessed 04.19.2016]

[12] Child Magazine, 2015, Do Fat Babies Make Fat Adults? Available at: http://www.parents.com/baby/development/problems/do-fat-babies-make-fat-adults/ [accessed 04.19.2016]