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The link between pregnancy weight gain and big babies

The link between pregnancy weight gain and big babies

By Heather Turgeon |

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A close friend told me recently that at one of her early pregnancy check-ups, her obstetrician told her she shouldn’t gain more than 20 pounds. My friend is a thin, incredibly active and fit soon-to-be mother of three, so I was surprised to hear such strict advice.

But her doctor is not alone in scrutinizing pregnancy pounds. Over 60 percent of women in the U.S. gain more weight than recommended for their body mass index, according to the Institute of Medicine. This trend, alongside growing evidence that a mom’s weight affects her baby in the womb, has brought the issue front and center for a lot of physicians.

A study published this year in The Lancet – a collaboration between Columbia University and Children’s Hospital Boston – was the latest to show that mom’s weight gain can affect her baby’s health. The researchers tracked more than 500,000 women and over a million babies, finding a significant correlation between mom and baby’s weight.

Women who gained upwards of 53 pounds were more than twice as likely to have a heavy baby (at least 8.8 pounds) as women who gained between 18 and 22. Women who gained between 44 and 49 pounds were almost twice as likely to have a heavy baby.

Since parents pass on weight tendencies through their DNA, the researchers had to sift apart the effects of genes from the effects of the moms’ weight gain. So they compared birth weights of multiple kids with the same mom, and the relationship between pregnancy weight and birth weight still held up. If a mom gained more with one baby than the other, that baby was more likely to be heavy.

Birth weight and BMI (body mass index) later in life are related, so scientists and public health researchers think pre-programming of a baby’s weight before he’s born could be contributing to the nation’s obesity epidemic. It’s a cycle, they say – as the population gets heavier, more babies are coming out of the gate destined to be bigger and at higher risk for heart disease and diabetes.

Needless to say, moms don’t like being scolded for the size of their bellies. It’s a double whammy – weight is already a sensitive issue for many women, and the overwhelming amount of advice and warnings we get from the womb police while we’re pregnant is just piled on. It’s a vulnerable time, so adding a tsk-tsk to your regular weigh-in feels horrible.

We can’t ignore the science, but maybe we need to put things in perspective. Yes, there is strong evidence that pregnancy weight has an impact on babies’ health (the study populations are large, and new data keeps re-affirming the connection). Scientists think that a mom’s fat stores send chemical signals that cross the placenta and become part of the uterine environment, affecting the way the baby’s own fat cells and metabolism develop and possibly altering the brain in small ways that translate into weight tendencies.

But the real concern is on the extreme ends of the spectrum. For example, in the early part of the 20th century, when weight recommendations were closer to 15 pounds, the risk was underweight babies and, accordingly, in the 1970s doctors started encouraging moms to pack it on a little more. Now doctors are most concerned with the opposite – overweight moms who tip the scales too much in the other direction.

In a way, it’s not such a controversial idea after all: The extremes aren’t good for us. Or our babies.

In fact, researchers say it may be a woman’s pre-pregnancy weight that matters as much or more than what she gains with her baby, which is also part of the problem with telling moms to tighten up their belts. You can’t just set ideal weight standards and tell pregnant women to figure it out – moms need support for staying healthy in pregnancy. Sure, there is an element of indulging for some women who finally feel they can cut loose when they get pregnant. But we can’t deny that the same barriers to health for the general population – like a food system set up around processed foods, not whole ones – is also to blame.

But here’s something that might help take the spotlight off mom for a minute: Last month, a Nature paper suggested that dad’s diet affects his child’s health, too. Through chemical tweaks that take place in the sperm, fathers were found to pass on unhealthy dietary effects to their babies.

Researchers at the University of New South Wales in Sydney, Australia fed one group of mice an unhealthy diet and the others a well-balanced one. As expected, the ones they beefed up got fat and showed signs of type 2 diabetes. When the groups went on to have babies, though, the dads who had been overfed were more likely than the healthy ones to have babies with symptoms of type 2 diabetes.

It’s a provocative idea – that in addition to transferring genes that code for weight tendencies, dad could pass on the effects of his lifestyle, healthy or unhealthy. The researchers’ guess that ‘epigenetic’ factors are at play – these are not changes to a dad’s DNA code, but changes to the signals that turn genes on and off.

In the end, the question of weight is complex, and studies like these point to differences across the population, not necessarily in your home (which is why “but I gained more weight and my baby is fine” misses the point – that’s not how studies work). Of course we need to approach the topic with sensitivity and empathy for the bind some moms feel. But we can’t just say it’s unfair to focus on pregnancy weight when we’re so diligent about everything else we do for our babies.

The Institute of Medicine’s weight guidelines

BMI pre-pregnancy Recommended pregnancy weight gain
28 to 40 lbs
18.5 – 24.9
25 to 35 lbs
25 – 29
15 to 25 lbs
11 to 20 lbs

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About Heather Turgeon


Heather Turgeon

Heather Turgeon is currently writing the book The Happy Sleeper (Penguin, 2014). She's a therapist-turned-writer who authors the Science of Kids column for Babble. A northeasterner at heart, Heather lives in Los Angeles with her husband and two little ones. Read bio and latest posts → Read Heather's latest posts →

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23 thoughts on “The link between pregnancy weight gain and big babies

  1. Rosana says:

    I agree, weight prior to pregnancy is more important. If a woman is not overweight before pregnancy, keeps exercising her body just go back to the same weight as before with minor differences.
    For me, pregnancy weight has come off in the first six weeks postpartum so I feel that it is not fair to call it “baby weight” since that comes off right after the baby comes out :) and the rest takes care of itself. The weight left is from not exercising or following an unhealthy diet.

  2. wohm says:

    I think limiting food intake during pregnancy can be dangerous. There are other studies showing a limited diet will predispose the fetus to conserve fat after birth and into adulthood. I gained 75 lbs during pregnancy and my daughter was born with the exact same birth weight as me (around 7.5 lb, my mother had only gained 30 but was far more active). I’ve lost most of the weight without trying (most within the first month) and my daughter is now very skinny. Everyone is different, I think it’s more important to eat what you feel like and have moderate exercise. I will say I felt uncomfortable with an extra 75, but have nothing else to compare it to.

  3. Lucky says:

    I was 100lbs at the start of my first pregnancy. I’m 5’2″. I gained (stopped counting at) 50 lbs and had a 9lb 2oz baby. The thing was, no one could have told me not to gain so much weight. I was HUNGRY. With my daughter I wasn’t as hungry, didn’t gain as much weight, and she was 7 lbs. For the record. They’re both in the bottom 10% and growing steady. I don’t know what happened to my son but he was never obese. And we’re now all a happy “little” family. :)

  4. Kari says:

    I’m only 28 weeks and have already gained 25 lbs. My biggest concern is how big the baby will be and a vaginal birth. My first child, I gained 43 lbs, but started out at 120 and was 5’9″. He was almost 7 lbs at 34 weeks. He would have been like 12 lbs if he went full term!! Ultimately, I want what everyone wants, healthy baby, but if the healthy baby could come in a smaller size and I could control how much weight I am gaining (i exercise and do not subscribe to the ideology that I can eat what I want because I am pregnant), I would be less worried.

  5. Jess says:

    I was about 122 lbs when I got pregnant with my son. I gained about 50 lbs. and gave birth (vaginally, no drugs) to a BIG boy…about 9.5 lbs. But now my son is two and has been in the 15-25% area of the weight chart for over a year. Being big at birth does not necessarily mean staying big. And I don’t think I over-ate during my pregnancy either…although I will say that the next time I’m pregnant I am going to think about reasonable ways to perhaps have a slightly smaller newborn. Cuz 9.5 lbs really FELT like 9.5 lbs.

  6. aaa replicas says:

    i wasn’t very big when I had my baby and he was very healthy and weighed 7.2kg.

  7. dbee says:

    I’m just curious; do women really have that much control over what they gain?

  8. Cyndi says:

    There was a brand new study done that was in an article in Oct 4th Time magazine. The study was done on a group of women who had babies before and after gastric bypass. The babies birthed before gastric bypass had a higher risk of being overweight and the latter born babies processed fats and a carbs better than the before children. That really did it for me, I’m watching my weight carefully during this second pregnancy to do everything I can to prevent my weight struggles for becoming my kids’.

  9. brex says:

    I just read the book Origins and it said that the higher the birth weight, the lower the chance of heart disease in later life. Where does that fit in?

  10. terram says:

    I can’t help but think that weight gain is such a touchy subject in part due to our culture of weight issues for women. I’m on the small side (5’4″ and 115) and although I never considered myself weight obsessed, when I was pregnant I was thrilled that I could eat whatever I wanted without judgment (or so I thought) and people actually CONGRATULATED me on the weight gain. My grandmothers nodded appreciatively at my expanding girth and everyone seemed to love that that I was growing bigger and bigger. For the first time in my adult life I had a license to eat without guilt. That strikes me as more than a little screwed up, but I’ve heard the same sentiment echoed by friends. I can’t help but think that contributes to large pregnancy weight gain for a lot of women. And for the record, I gained about 40lbs with both kids and lost it within a few months through b.feeding and sensible eating. My babies were on the large side (about 8.5 lbs each), but I would still say that one of the best things about pregnancy was the food :)

  11. science of kids says:

    brex: i haven’t read origins yet, but i think up to a certain point, when birthweight goes up, health issues like heart disease go down. when it goes up too much, that’s when health problems also start. i gather that the extremes on either end aren’t good.

  12. Kanoealoha says:

    I think it’s odd that they just look at weight gain. My mother has always drilled into me it’s not the weight gain, it’s the type of weight you gain. You can gain it from junk food or you can gain it from healthier food and it will make a difference. I follow the Brewer Diet when I’m pregnant and it is protein intensive and runs about 2,300 calories a day, so for some that equals weight gain for others it equals weight loss.

    As always it’s about weight and not about a healthy diet (and by that I mean lifestyle, not weight loss program).

    And this is coming from a woman that is considered obese and had a 7 pound baby 5 days past due date, though I did only gain 25 pounds and I did not have GD or any other complications.

  13. rally for moms sanity says:

    I’m so glad that scientists have come up with a NEW way to make moms and moms to be even more neurotic. I see a chicken-n-egg situation here myself. After my daughter took her sweet time making an entrance into the world (almost 2 weeks past due date), I am pretty sure that the baby’s DNA has to be a factor in this equation. Maybe the baby was pre-programmed to be bigger and the mom needed to gain more weight in order not to topple over with the weight of the baby? Why is it always have to be cause (mom) to effect (baby) in these highly complex feedback systems??

  14. Purebebe Heather says:

    “Birth weight and BMI (body mass index) later in life are related, so scientists and public health researchers think pre-programming of a baby’s weight before he’s born could be contributing to the nation’s obesity epidemic. It’s a cycle, they say as the population gets heavier, more babies are coming out of the gate destined to be bigger and at higher risk for heart disease and diabetes.”

    Sorry to be the nay sayer, but this is complete BS and I hope that the moms reading this article don’t start binging while they’re pregnant. I would LOVE to see the numbers (and to know WHAT researchers) back up this claim.

    I read The Lancet article and agree that a mother’s weight gain and a baby’s birth weight are correlated. But where’s the research that backs up the claim that a baby’s weight gain has anything to do with their weight later in life?

    Personally I had an almost 10 pound baby (and another 8 1/2 lb baby), gained ~40 pounds with each (ate healthy, organic foods during both pregnancies) and neither my husband nor myself are overweight or have ever been overweight. And no gestational diabetes either.

    Everything I’ve read has been the complete opposite – women who are overweight are an an increased risk of delivering babies pre-term, and thus lower weight babies (surprisingly, those babies were NOT included in the Lancet study since they excluded babies born before 37 wks).

    A baby’s birth weight has to do more with genetics and the length of the pregnancy more than anything else.

    -Heather (

  15. I Sell Books says:

    I’m a fat woman who gained a total of 17lbs during my pregnancy. My son weight 7lbs 2 1/2oz at birth – and my doctors told me that unless other issues cropped up, they wanted me to eat real food when I was hungry, and not to binge…and that was it.

    What I find interesting is that it was the thinnest women in my group who gained the most weight, 50lbs or more, while the fat ones gained less than 20. I’m just sayin’…

  16. sara says:

    This is so individual and every woman is different. My doctor was on me about gaining weight (60 pounds and I’m already overweight). Then she realized I have fabulous blood pressure, no gestational diabetes, and my baby is big for his gestational age. It’s GREAT that he’s big because he will be born early due to a birth defect.

    Also, food deprivation was impossible. I was totally insatiable the first trimester- I felt like I was starving an hour after eating a full meal.

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  18. Overthinking Mom says:

    I wish I hadn’t gained so much weight with my pregnancy, but I actually think genes had something to do with it. I naturally weigh 110 pounds at 5’4″ and gained over 40 pounds, giving birth to an almost 10 pound baby (with no diabetes). I honestly didn’t change my eating habits much during pregnancy, other than during the first trimester when I had severe morning sickness. I gained most of the weight in my belly and I lost it without dieting four months later. My mother is also petite and had large babies. Some women just have big babies naturally. I wish my daughter had been smaller for vanity belly reasons, but she was born healthy and continues to be healthy. Not all weight gain can be controlled by the mom.

  19. Tricia B says:

    I don’t agree with this. I’ve had 3 large babies and the most I’ve gained was 26lbs. With my largest, 10lbs 7oz at a week early, I only gained 16lbs. I ate well during all my pregnancies although I craved milk, but that wasn’t abnormal for me. My husband was a large baby, and I was big but not huge at birth. My husband is now a big guy. I never had gestational diabetes. I think that some women just have large babies.

  20. betty g says:

    I gained 40 with my first pregnancy and 35 with the second. I was right on track, right up until my third trimesters. Then my weight went up like a balloon. Like my Mom, I am prone to water-weight gain. No controlling that. And my doctor wasn’t really concerned.
    So my question is this; if the researchers were purely tracking weight gain, how did they account for water-weight? I am skepticle about this study because it seems there were just to many variables they could not account for. At the end of my pregnancies, who was to say how much gain was due to fat and how much was water?

  21. Travon says:

    Phnenomeal breakdown of the topic, you should write for me too!

  22. Lydia says:

    The logic in this seems a bit flawed to me… Or at least it was very inaccurate for me. :-)

    Baby #1. — gained 45 ponds… Daughter was 6 lb 13 oz

    Baby #2 — I LOST weight without trying until last month. Only ended up +7 for the whole pregnancy. Couldn’t eat meat, craved salads, avocados, polenta, etc. my son was a BIG 10 lb 4 oz and healthy as an ox. He is in the 95% for his height now and skinny.

    Baby #3 I lost weight again for some reason until 6 months. Only ended up +12 lbs. Baby again was big at 8 lbs 11oz.

  23. Kelie says:

    I dont agree at all.
    I have been told not to put on any more weight by my midwife as i will end up having a big baby…
    With my first child i went from 50kg to 126kg, so i gained 76kgs – He was 7 pound 12 ounces.
    Second baby i went from 50kg to 70kg, so only put on 20kg, and was 56kg lighter when i had her compared to my son, and she was slighter bigger at 7 pound 13 ounces.

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