Weight Gain in the Second Trimester: A Sudden Bump Up Is Common — And No Reason to Panic

Weight gain during pregnancy is not steady. Most women gain the most weight in their second trimesters, and much of this weight is water.

24 weeks into my first pregnancy, I was feeling smug. I had been eating right, continuing to exercise, and the last dregs of first trimester nausea and fatigue had faded. I was feeling good.

That is, until my OB took me down a few notches at my 6 month appointment.

She told me I had gained “too much weight”. She passed the chart. It was all there in black and white.

Although I had been on target to gain the “correct” amount of weight by the end of my pregnancy, I had gained a whopping 8 lbs in a month. I was now on a trajectory to gain over the upper limit of 35 pounds. She began what was clearly her set lecture. “Eat less bread. Eat only half of the sandwich…”

But as she spoke, my mind began to wander. I was pretty taken aback. I silently reviewed my recent eating habits. No, I did not think they had changed. Certainly not enough to cause a gain of 8 lbs in a month. And yes, I had been exercising my normal amount. If anything, I had become more active in my second trimester. My energy levels had gone up in the last couple of months, not down.

Convinced that I had done nothing dramatically different in the last month, I started to wonder whether we could accurately or reasonably expect a steady rate of weight gain. Maybe it’s normal to gain a lot of weight in the middle of pregnancy, and less towards the end. Maybe pregnancy weight gain looks more like a curve than a line.

So I went home and did a little searching.

I found the 2009 Institute of Medicine (IOM) research review on pregnancy weight gain, the source of the current weight gain guidelines: 25-35 lbs for normal weight women, 28-40 lbs for underweight women, and 15-25 lbs for overweight women. (Most pregnancy-oriented sites repeat these guidelines, but provide no explanation of why those amounts are recommended.)

To be clear: I don’t have a beef with guidelines. Guidelines are useful for medical practice. But we have to remember that guidelines derive from messy data, incomplete information, conjecture, and compromises made by a committee.

All too often, once codified, guidelines become elevated above all their underlying messiness and instead become rules.

So, let’s go back to the actual data, to what we actually know about pregnancy weight gain.

1. First of all, a sudden bump up in weight in the second trimester, like the one I experienced, is not only common, it is the norm.

“The pattern of GWG is most commonly described as sigmoidal, with mean weight gains higher in the second than the third trimester across BMI categories, except for obese women.” – IOM 2009 report, pg. 101.

2. Pregnant women do not gain weight at a consistent rate from week to week. Not during a whole pregnancy, nor from the second trimester on. Studies that track the rate of weight gain find a pattern of gain that looks more a side-lying S than it does a straight line.

This is because women usually gain the the largest amount of weight in their second trimester. And this in turn is because…

3. Most of the weight gained in the second trimester is water. Compared to fat, water weight can come on very fast. In the second trimester, blood volume increases by almost 50%. This is why many women experience extreme thirst in their second trimesters.

“Plasma volume increases progressively to 50 percent by 30-34 weeks of gestation.” – IOM 2009 report, pg. 93 

By the third trimester, the ramp up in blood volume and amniotic fluid is largely behind you. Weight gain tapers off. In fact, in the last month of pregnancy, many women gain almost nothing or even lose a couple of pounds.

Chart Title: Where the Weight Gain Comes From, Week by Week

Components of Pregnancy Weight Gain By Week

*Note that this chart shows a linear weight gain, which is inaccurate. I include it because it is the best chart of the components of weight gain I have seen, despite this misrepresentation.

 As shown in the chart above, much of the gain in the third trimester is fat. But there is an important caveat. Swelling in your arms, legs, hands and feet–what doctors refers to as edema–varies a lot from woman to woman and can have a big impact on third trimester weight gain. In the third trimester, women may gain anywhere from one to nine (nine!) additional lbs of water weight from swelling. And this is completely normal.

 “Total body water accretion is largely under hormonal control and is highly variable during pregnancy…. For a reference 12.5-kg GWG, total water gain at term is distributed in the fetus (2,414 g), placenta (540 g), amniotic fluid (792 g), blood-free uterus (800 g), mammary gland (304 g), blood (1,267 g), and ECF (1,496 g) with no edema or leg edema and ECF (4,697 g) with generalized edema (Hytten and Chamberlain, 1991).”  – IOM 2009 report, pg. 78

In addition to swelling, the amount of amniotic fluid present in the third trimester varies by up to 2.2 lbs.

“Given the wide range of normal amniotic fluid volume at term, this compartment may affect maternal GWG by as much as 1 kg.”  – IOM 2009 report, pg. 92

Adding this up, in the third trimester alone, women with perfectly normal, healthy pregnancies can vary in their water weight gain by up to 11 lbs.

Why do I bring this up? For me, the wide range of water weight gain underscores how hard it is to determine the “right” amount of weight gain for any woman. What might be a reasonable gain for one woman, consisting of a small amount of fat, would translate into an additional ten or eleven pounds of fat for another.

I often think on this 1-11 lb. range in reference to my own postpartum weight loss. Despite gaining within the recommended amount for both of my pregnancies (30 lbs), each time in the first month after delivery, I shed only about 15 lbs. My friends who exceeded the guidelines and gained 35, 40 lbs? They all dropped 20 to 25 lbs in the first couple of weeks!

But they, of course, had swelled up like water balloons in their last few months of pregnancy, while I had not.

This realization, more than anything, persuaded me that we–medical establishment included–all need to relax about the number on the scale, and the rate of weight gain.

What was your experience with gaining weight in pregnancy?

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Author: Amy Kiefer

I am a research scientist and mother of three munchkins. I live in the Bay Area and when I am not child wrangling and catching up on lost sleep, I love digging into the research on all things fertility, pregnancy, and breastfeeding related.

33 thoughts on “Weight Gain in the Second Trimester: A Sudden Bump Up Is Common — And No Reason to Panic”

  1. I still remember my old OB getting on my case for being a few pounds over the recommended limit. This is part of the reason I changed OBs mid-pregnancy. I had enough to worry about (work, vaccinations, breastfeeding, etc). Post baby figure wasn’t really high on the list.

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  2. Great post! Having gained ~30 lbs during the first two trimesters, and having heard that the baby grows dramatically during the third trimester, I was expecting to significantly overshoot the weight-gain guidelines during my upcoming third trimester. It’s good to know that’s both a bit less likely and a bit less worrisome than I’d originally thought.

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    1. For what it’s worth, my personal experience was consistent with the research on this one. My weight gain definitely slowed down in the last couple of months.
      I am curious how much of the slowdown is due to an increase in metabolism. Let me know if you find any good studies on this topic.

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  3. I have been feeling great (33 weeks now) about my body, but have been reminded constantly by my OB that I’ve gained weight quickly. When did this start? 2nd trimester. How much extra weight have I gained? About 5 lbs. But enough to feel like the nagging has been incessant. And of course, because it’s not just ME anymore, I have felt pressure to change the rate of weight gain. At the worst point, around 23 weeks, my doctor had me restricting calories. I was essentially starving, as the baby grew but I didn’t. Last week, at the 32 week appointment, my doctor seemed pleasantly surprised to see that my fundal height is on target despite the fact that I’ve gained (gasp) 5 lbs beyond the recommended weight gain for 40 weeks. How much emotional stress and anxiety could have been avoided in weeks 20-32 without pressure from the doctor? Would a happy stress-free mama outweigh the risk of an extra 5-10lbs over pregnancy? I sure think so, especially considering that it might be a non-risk after all.

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    1. I’m glad that you are feeling great and that you know that is the most important thing! I totally agree, a narrow emphasis on weight gain ignores other considerations like stress and overall health.

      In Expecting Better, Emily Oster has an excellent discussion on this topic as well. Have you read her book?

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  4. This is a great post, I sent it to a pregnant friend right away! I started out borderline-underweight, didn’t gain any weight in the first trimester (too nauseated), then gained 60 lbs in the next two. I gained it very consistently (about 2 lbs a week), much to my horror, but neither of my doctors (I moved when I was 25 weeks) had anything negative to say about it. In fact, they didn’t say anything about it at all (except not to worry when I expressed aforementioned horror). I worked out five days a week and my diet was reasonable overall (I had just moved back to the States, so I may have gone a little nuts with things I couldn’t get abroad, like, tacos or good ice cream, but I ate a lot of fruits and vegetables and cooked at home for the most part). I don’t know if that would’ve been different if I had started out overweight (or wasn’t so tall, where the weight is spread out and less noticeable), but it was a relief not to have to deal with that kind of stress on top of everything else.

    I lost about 30 lbs within six weeks, and then just stopped losing weight for the next year or so. I even gained back some of it. As a person who’s never had a problem with losing weight, it was a really stressful and depressing time. By about 13 months postpartum, I was back to a weight that felt normal for me (still 15-20 above where I was, but totally normal BMI-wise), and now it’s 15 months and I’ve sustained that. I couldn’t believe what a toll breastfeeding took on my body in terms of being constantly starving–something I didn’t experience in pregnancy–and depleted of all energy. I exclusively breastfed until seven months and that was a difficult time. I slowly got back into exercising regularly, but the hardest part for me has been having to re-train myself to eat reasonable portions of food. I still pump 2-3 times a day, but I’m at a comfortable-enough weight for now. I don’t expect to lose the last bit (at least another 10 lbs) until I’m totally done producing breast milk.

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    1. Thanks for sharing your story! I have also had a hard time taking the weight off postpartum, despite breastfeeding. From what I have read, the research is mixed on whether breastfeeding helps take the weight off. It certainly did not seem to help me! A good topic for a future post.

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      1. My doctor warned me that I probably wouldn’t finish losing weight until after I weaned, so those words have given me a lot of hope through this time. I wish easy weight loss wasn’t so often touted as a benefit of breastfeeding.

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  5. This agrees with my experience as well. Peak weight gain for me was between 4 and 5 1/2 months. I have a very detailed chart thanks to Withings, and the slope is very different during that window!

    It then slowed a lot in the third trimester until the very end when I gained 5 lbs in the week before I delivered, pushing me over the recommended max. I did not appreciate the questions from my doctor about how much I had been eating that week. Did they really think I had suddenly started eating an extra 3000 calories a day with my tiny, compressed, full-term stomach? Ooof, no thank you. My feet and ankles were suddenly enormous, and sure enough, one week after birth I was down 22 lbs with my feet and ankles back to normal. (Unfortunately despite this initial big drop the rest of the weight had no interest in going anywhere).

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  6. I gained 33 lbs my first pregnancy, just like other women commented within a week or two post partum, almost all was gone. I found this blog because I’m 18-19 weeks now and I gained 3.5 lbs in less than two werks but my blood pressure is great and no swelling. I was a bit worried, but as a scientist I like actual science to quell my fears. I went into pregnancy overweight so I’m going to increase my exercise and I’ve already drastically cut out sugar due to exasperating benign PVCs I have…..cardiologist told me to stop worrying and relax, I said I’ll try but I have a 2.5 year old toddler and this pregnancy is making me feel like crxp!

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    1. Thanks for the comment! Based on the research, your weight gain sounds totally normal. I also had a big bump up in weight around that time. Your blood volume is increasing dramatically, so it is probably mostly water! My guess is that your weight gain will taper off in a month or two, once this increase is behind you.

      And it’s so true, my second pregnancy was so much harder, in part because I was chasing a toddler the whole time. Hang in there!

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  7. I had an interesting pregnancy. Decently fit before getting pregnant. I am 5’8 and liked to stay at an athletic 150/155lbs. (played soccer 10 years) I was 155lb pre pregnancy. Eating heathy- snacking every 2 hours. I didn’t re-start working out till 11 weeks along- just to be safe. If my 1st triemester I gained 11lbs, and could tell by how my clothes fit or didn’t fit- but didn’t look any different except a bloated look. I then worked out for 45 minutes to an hour 5x week. Weights, stair master, stretching/yoga. I gained a whopping 33lbs in my 2nd trimester. I gave birth to my daughter 6 weeks early. At 34 weeks I was 210lbs. At this point I had gained 55lbs. I gave birth to a 5lb 5oz healthy baby girl and dropped down to 183lbs- that was 2 days after birht. I was pumping lilke crazy and could have fed all the babies in the hospital. I am not sure if that helped with my losing of weight so fast, but to drop 27lbs. I am almost 20weeks today and have already gained 25lbs!! This one is a boy. I started at 165lbs, more inshape than 1st time around and don’t look like I’m 190lbs at all. Dr. was concerned how I gained 10lbs in 1 month, and I told her I have no idea. She said, you must be part of the small percentage of women who gain a lot of weight and have nothing to show for it except a growing belly. All women and pregnancies are different. Can only gage on how you feel and what your blood/urine tests says.

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  8. Started at athletic 155lbs. gained 11lbs 1st trimester. 33lbs 2nd, and 11 into the 3rd. I gave birth at 34weeks to a 5lb 5oz baby girl. Healthy and ready to come out. I was 210lbs at delivery and dropped to 183lbs post delivery.

    This time I am having a boy. Started in way better shape that the first. I was a solid 165lbs. I gained 5lbs 1st trimester—but also had morning sickness. I have gained already 20lbs and am 2 days from being 5 months. The Dr. even asked how I gained 10lbs in 1 month but concluded that some women just gain a lot of weight and don’t look like it. Everyone is baffled that I am only 5 months and already 190lbs. I assume my kids like room in the belly. Or I have dense muslce and retain water. Who knows. I just care to have another drug free, painless, easy delivery like my first.

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  9. Thanks for this post! I’m a scientist myself but have been following online weight gain calculators (my midwife – we don’t see the obgyn here in Sweden unless something is wrong – hasn’t been worried even if I started at BMI 29). I definitely started over weight but eat very well and am at the gym at least three times a week.
    Until week 26 I was happy. Had gained only 4 kg (ca 8 lbs) since the start. Then came Christmas, a food trip to Paris and my birthday. Lots more sugar than before but still regular workouts and lots of veggies. But in five weeks I have gained 5 kg (11 lbs) and now in week 29 I’m over the suggested limits. At the same time came headaches, backache and seriously swollen legs, arms and feet. And the worrying. Am I gaining too fast for the baby’s health? Can I stop it? Will I get diabetes? Will I gain this much every week for the rest of the pregnancy?
    Your post makes sense. I’m sure some of my weight gain is from eating too much over the holidays but I didn’t pig out. I’ll try to cut out sugar completely now and as soon as my pelvic pains calm down a little bit, I will up my excercising. But really, water could be a big part and so could the phase of growth the baby is in (in the last two weeks he has also gotten very much more active!).
    Thanks for reminding me it’s normal not to have a straight line and that my last few weeks are not necessarily an indication of how the curve will look every week from now on!

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    1. Kudos to you for working so hard to have a fit, healthy pregnancy! I would not worry about the second trimester bump. My guess is that the weight gain will taper off in the last couple of months. That is how it’s gone for me and so many of my friends, and what research shows as well.

      As for the food trip to Paris, I am envious.

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  10. I am almost 27 weeks along, and have gained 8 pounds in the past month. 16 pounds total over my whole pregnancy so far. I am considered “obese” meaning my OB only wants me to gain up to 20 pounds, which I consider unfair. It’s like practicitioners can’t even comprehend the possibility that an overweight pregnant woman could still be healthy. My blood pressure has been fine, lower than it was before pregnancy. So far I am not gestationally diabetic. Yet my practicitioner is talking about me poking myself as a way to regulate my weight all because I gained 8 pounds in the last month. This is the first big weight spike I have had. I haven’t been pigging out. I do indulge every now and then, but what pregnant woman doesn’t? My practitioner was all over me yesterday because I gained 8 pounds in a month. She said “You have definitely gained WAY too much.” I was already upset by the fact that I had gained 8 pounds in a month and she made it worse. She started going on about how I need to see a dietician and possibly start poking myself. It’s ridiculous! I also think that overweight pregnant women are treated worse by their OBs. I don’t really look different except for in the stomach. I work out and count calories.

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  11. This is the most reasons article I’ve found pertaining to weight gain during pregnancy. I’m 17 weeks today, and gained 4 of the 7lbs I’ve gained in the past week. Thank you for easing my fears. I’m going to relax and accept the way my body is growing and changing.

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  12. Thank you so much for your blog!! It has made me feel so much better about my weight gain. I had a bmi of only 18.5 before pregnancy. And at first I only gained a few pounds, up until about 20 weeks. Since then I’ve gained 2 pounds per week consistently (I’m 25 weeks now). I was worried that I would continue to gain 2 pounds a week until the end, but you blog makes a lot of sense and has reassured me a lot. I like to see evidence behind the numbers, so thanks for backing it all up!

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  13. I’ve been extremely concerned about my rapid weight gain, which has been since week 10. I have a history of great difficulty losing weight, but I had lost 65 pounds since 2009 & kept off 60 of it with a steady weight over the 6 months prepregnancy, during which I was taking a weight loss break. I track diligently because I am Type II Diabetic (normal glucose levels from diet, exercise & Metformin) & am a numbers geek. I weigh foods on a scale in grams. I am serious about this.

    Since I became pregnant, I have been eating slightly less (85 calories less) than those 6 months of maintenance & doing slightly more (56 calories extra) exercise daily, an hour of cardio on my arc trainer, plus weight training twice a week started in the second trimester. Still, starting in my 10th week of pregnancy, I have had big jumps of 3-6 pounds overnight which just never went away, over and over again, and at 19 weeks, I am now at 18 pounds heavier than I was at conception. I have averaged a weight gain of 2 pounds a week for the past 9 weeks, despite being at a small deficit daily.

    I am prone to big fluid fluctuations, even when I am not pregnant, but this has me worried. I am 5’11” tall & large frame, overweight by body fat percentage (37%) prepregnancy. My doctors seem unconcerned because they are so impressed with my blood glucose levels being normal; they all insisted I would need insulin, but they don’t know my life!! 🙂 My diet is extremely healthy; I only eat organic grass fed lean beef, organic chicken, turkey & wild caught fish, organic fruits & veggies, organic dairy & some nuts (though I have to be careful as they can give me eczema if I have them daily). I am allergic to potatoes, shellfish, all grains, all legumes, various seeds, etc, so I don’t eat any of those. I am worried I will end up gaining another 40+ pounds if things keep up at this rate. 😦

    I am wondering if I should increase my exercise to weight loss levels. For me, that is 2-3 hours (moderate intensity) per day, minimum, since I have such a hard time losing weight. I don’t want to do anything that would be risky for the baby, but I am thinking this much weight gain, so rapidly (I just gained 6 pounds since yesterday) can’t be good. My blood pressure & blood work in general is all excellent. I am at a loss.

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    1. This is probably a bit late, but i wouldn’t be going for weight loss in preg. It sounds like you are doing all you can – excellent diet, regular activity. I worry about my weight sometimes too but all i can do is focus on eating well and being active (without overdoing it – i have had chronic fatigue so i have to respect my body’s limits these days (i used to be mega mega active!)). I think my body type is just naturally muscular and a bit curvy, so i figured this would come out in pregnancy. I know surges of early, unexplained weight gain can indicate preeclampsia/something similar maybe????
      Don’t be too hard on yourself or your body. It can be hard to let go of weight issues in pregnancy when it is all largely out of your control. When the baby is out and weaned though you’ll be able to refocus. Good luck!!

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      1. Thank you for the response :). At 24 weeks, I’m 19-20 pounds above prepregnancy weight; I haven’t gained since 21 weeks, thanks to being able to do 2 hours a day on my arc trainer. My morning sickness returned today, though, so I am not sure how long I can keep that up. My blood sugar is still normal, numbers have actually gone down & the docs are super impressed. My blood pressure has remained excellent. I’m less concerned with the weight gain now because I am not getting the huge overnight fluctuations. I was really worried about pre-eclampsia. At sonograms, the baby has been right on point for measurements & all markers are perfect, so I am trying to let it go. 🙂

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  14. Someone posted this on a birth board I’m on and had commented on. Thank you! I gained 8 lbs in 6 weeks, from week 20-26, for a total weight gain of 18 lbs. I started off overweight but still nursing a 14 month old and 25 lbs below prepregnancy weight. My OB gave me this lecture on Friday and implied my chances of a VBAC were greatly diminished if I gained too much weight. While I don’t eat the healthiest, I do get in close to 10,000 steps per day and was on the weight main entrance diet I was on prepregnancy. It really punched me in the gut since my diet didn’t change and sent me into a tailspin as I tried to cut calories and find suitable replacements. While I will still reduce sugar intake, this article makes me feel better because as a scientist, I also was curious how they could expect you to gain at a steady rate when the fetus itself goes through growth spurts. Thank you!

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  15. I know this is an old article but just wanted to say thank you. I’m currently 24 weeks pregnant and I’ve gained about 16 lbs (21 if you consider the 5 I lost during the first trimester and then regained)…I was 143 preconception so a healthy weight. My doctor has been giving me a lot of grief about my weight gain and honestly it’s taken a lot of the joy out of my pregnancy. I’m eating healthy and exercising 3-5x a week so I’m not sure what else I can do to keep the weight gain “steady”. I know in my heart I’m doing my best for my baby and myself but it’s hard to hear that you need to do better every time you step on the scale at the dr. I’ve talked to enough women who have had similar experiences as me that I just feel like there needs to be more leeway with how weight is handled in pregnancy. I totally appreciate my doctors concern, I just wish she would offer some alternative reasons for the gain (as you did) as opposed to accusing me of gorging on junk food. Thanks again!

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  16. Thank you, thank you, thank you for this! Every freaking article I read harps on my only gaining 25-35 lbs! Well, by week 22, I’m up 25 already – “supposed to” be damned. I could exercise more, but I’m active and not a junk food junkie, so I’m not going to worry anymore. I’m tired of feeling judged and the doctor thinks I’m healthy – I’m lucky enough to have a lovely OB whose wife has had two kids. He knows better than to criticize weight gain, I think! He just warns it may be harder to lose lbs after birth if you gain too much during pregnancy. Most of my friends still carry an extra 10lbs but I think a baby is worth it!!

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  17. My weight ended up fluctuating between 33 & 43lb gained by 41 weeks pregnant. My baby is now 11 days old, and I am only 10lb heavier than I was pre-pregnancy, where I have been for about 6 days! About 6lb of this weight is breast gain (I weighed them, don’t ask). I exercised an average of 80 minutes per day on my arc trainer during my entire pregnancy & ate like an organic saint. I finally told myself to relax about weight gain. About 25 pounds was gained by the end of my 2nd trimester, and everything after that was water weight that came on in big overnight jumps. I have a healthy, beautiful little girl born 9 days overdue, so my body knew what it was doing & so does yours! ❤

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  18. This is such a great article! It really reinforces how weight gain affects people differently. I’m currently 24 weeks pregnant and noticed that my last doctors appointment that my weight shot up a little faster than I expected. I am up 17lbs now which I think is reasonable but don’t want to obsess over the scale and being at a certain number. Your body knows what it needs to do so try not to overthink things. A lot of the information in this article makes perfect sense. Thanks again for info!

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