Jun 17, 2024 • 14 min read

Why Am I Gaining Weight Fast During Pregnancy? First Trimester & On

Medically Reviewed by Kim Langdon, MD on 3/23/2023
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The phrase, “I’m eating for two,” is often heard by women at the dinner table (or vending machine, grocery aisle, or fast-food chain) as a way of indicating that they have a license to eat whatever they want while pregnant.

While this statement is true, it is incredibly misleading, especially when you realize that your eating “partner” often weighs less than 7 pounds. Gaining weight is an inevitable and important part of having a baby; however, 48% of new moms gain more than the recommended pregnancy weight gain.

Even when we think we’re eating well during pregnancy, gaining too much weight but eating healthy is still a possibility. Sudden or rapid weight gain during the first and third trimesters is very common, even when we’re not eating a lot.

What causes this, and is it something to worry about?

There are many reasons for rapid weight gain during pregnancy that are of no concern whatsoever. Your blood volume begins to increase to accommodate the new baby’s needs as early as the first trimester. You also make more blood cells to help supply nutrients to the baby. Each of these issues can cause weight gain.

There are other reasons for sudden weight gain in pregnancy that you need to be more concerned about. Extreme pregnancy weight gain, particularly after 20 weeks gestation, can mean you’re at risk for a pregnancy complication known as preeclampsia. Rapid weight gain in pregnancy from diabetes or gestational diabetes might also mean you should be concerned enough to visit your healthcare provider.

This guide goes over reasons for fast weight gain during pregnancy, how much weight gain is healthy during each trimester, and how to maintain a healthy weight during pregnancy.

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Why am I gaining weight so fast during pregnancy even though I’m not eating a lot?

The optimal amount of weight you should gain depends on your pre-pregnancy weight and other factors. In general, if you are underweight before getting pregnant, you need to gain more weight for a healthy pregnancy than if you were overweight when you got pregnant.

According to the National Health Institute (NIH), the recommended weight gain in pregnancy is as follows:

  • Normal weight before pregnancy –The recommended weight gain is 25 to 35 pounds.
  • Underweight before pregnancy –The recommended weight gain is 28 to 40 pounds.
  • Overweight before pregnancy –The recommended weight gain is 10 to 25 pounds.

What goes into the pounds you gain during your pregnancy? Surprisingly, very little of it comes from a gain in body fat. The breakdown of weight you gain in pregnancy comes from a variety of sources:

  • The baby weighs between 7 and 8 pounds at birth.
  • The placenta weighs 1.5 pounds at the time of delivery.
  • The amniotic fluid surrounding the baby weighs 2 pounds.
  • The uterus at term weighs 2 pounds.
  • Your breasts increase in weight and are 1 to 3 pounds heavier.
  • Your blood weighs 3 to 4 more pounds at term.
  • You have extra fluid within your tissues that weigh 2 to 3 more pounds at term.
  • You have extra fat stores that add to about 6 to 8 pounds.

Your total weight gain by these guidelines would be about 24.5 to 31.5 pounds. Of these, about 10.5 to 11.5 pounds are lost the minute you have your baby (the baby’s weight, the placenta, and the amniotic fluid around the baby).

If you have no nausea concerns during your pregnancy and have a healthy appetite, you may already have a good explanation for the weight gain you’re experiencing. You are likely taking the “eating for two” advice too seriously and are eating too many calories.

If this is the case, you need to have a talk with your healthcare provider or a prenatal nutritionist as soon as you know you need nutritional advice—not so you can lose weight, but so you can learn healthy eating habits and can more carefully gain the recommended amount of weight during the remainder of your pregnancy.

On the other hand, if you’re not eating more than you normally do and the pounds are still piling on, what could be the reason for this? Fluid shifts are the greatest cause of sudden weight gain in pregnancy.

“Water weight gain” is more common and happens quite easily in pregnancy. If you drink 64 ounces (two quarts or about 8 glasses) of water daily, this amounts to 4 pounds of fluid that your kidneys must lose to keep your output the same as our input.

If, instead, some of the fluid sits around your ankles from standing all day in hot weather, for example, you’d easily gain as much as 4 pounds in one day alone.

Another cause of sudden weight gain in early pregnancy is constipation. Estrogen and progesterone levels increase dramatically in the first trimester, but these hormones can be a common cause of constipation at any time during pregnancy. Even a little constipation can lead to overnight weight gain.

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How much weight should I expect to gain during pregnancy?

Weight gain in pregnancy follows an expected pattern. You will begin to gain weight even when the baby itself weighs only a few ounces; this early gain in pounds helps prepare your body for the stresses of pregnancy.

While you won’t be eating for two large human bodies at any time during your pregnancy, you will want to eat more calories per day than you ate when you weren’t pregnant during most of your pregnancy. Your baby needs energy in the form of calories you eat in your daily diet, and there are serious consequences of not eating enough during pregnancy.

Ideally, you can ensure that the same calories are helpful in other ways by choosing foods high in vitamins, protein, and minerals, too. You can learn more about the best foods to eat while pregnant here.

If you’re planning on gaining the optimal or “recommended” weight gain during your pregnancy, you’ll want to break down the amount you expect to gain each week and see where the weight will be on your body.

First trimester weight gain & calorie target

Your weight gain during the first few months of your pregnancy can be little to nothing, especially if you began your pregnancy at a normal weight. The good news is that if you’re suffering from nausea or vomiting during early pregnancy (aka “morning sickness”), you aren’t harming your baby if you don’t gain weight or even lose a few pounds.

You should eat about 1800 calories per day during the first trimester if you aren’t an avid exerciser.

This number doesn’t represent any more calories than are recommended if you weren’t pregnant. The big difference in your diet might instead mean you eat smaller meals more frequently (about 6 times daily) to avoid nausea and heartburn/acid reflux that are common during pregnancy.

Another difference in your first trimester diet involves your food choices. Your baby needs folate for brain and spinal cord health and to make new blood cells. Examples of good foods to eat during the first trimester that include folate are:

  • Beans
  • Peanuts or sunflower seeds
  • Whole grain wheat or rice
  • Dark leafy green veggies (spinach, broccoli, asparagus, other greens)
  • Whole fruits or fruit juices
  • Eggs

Because folate is so essential, you should talk to your provider about a folate supplement to ensure you get the recommended 0.4 to 1 mg of folate intake per day.

The American College of Obstetrics and Gynecology says that a weight gain of 1 to 5 pounds in the first 12 weeks of pregnancy is optimal and well within a target goal for how much weight you should aim to gain during this time.

Second trimester weight gain & calorie target

You will begin to require extra calories each day in the second trimester.

The recommended daily amount of caloric intake in the second trimester is 2,200 total calories.

Fluid intake should involve mostly water or low-calorie beverages, and you should try to drink 3 liters per day. This is about 12.5 cups of water per day. In addition, you can get fluids by eating fruits like watermelon or citrus, along with dairy products and certain vegetables. Vegetables also add vitamins A and C, magnesium, and iron to your diet.

During the second trimester, you should see a weight gain of about 0.5 to 1 pound per week. This is not all weight that goes onto your baby’s body, naturally. Instead, your increased blood volume, blood red cell count, uterine size, and fat stores account for this gain in weight.

Note that from here on out, it’s not safe to lose weight during pregnancy.

Third trimester weight gain & calorie target

In the third trimester, you can increase your daily caloric intake even more to include 2,400 calories per day.

This still isn’t a huge increase from your nonpregnant dietary requirement. 600 extra calories in one day are approximately the number of calories you’d consume in a restaurant-style cheeseburger with fixings, one plate of spaghetti with meat sauce, or a large cobb salad with ranch dressing.

Again, you should drink up to 3 liters of fluid per day even if you have a little excess puffiness around your ankles or a slightly puffy face (unless your healthcare provider instructs you otherwise).

However, you should avoid eating salty foods like peanuts, popcorn, or prepared soups. Water doesn’t cause fluid retention; salt does.

Continue eating healthy foods, including proteins found in lean meats, beans, quinoa, fish, eggs, and poultry. Your baby is continually making essential proteins to gain body mass, muscle, and enzymes. Only the protein in your diet can provide the amino acids to make these proteins. Learn more about how much protein you need during pregnancy here.

Healthy fats are also essential for your baby’s health. Fats are great energy sources and help make critical cell membranes (new cells) throughout your baby’s growth period in utero. Healthy fats are found in avocados, olive oil, and even lean meats and poultry. Fats are never your enemy, and they are especially important to eat during pregnancy.

As in the second trimester, 0.5 to 1 pound of weight gain per week should be your goal in the third trimester of pregnancy. More of this weight goes into increasing your baby’s size than in the second trimester. Increased body fluid and fat stores account for the rest.

How to maintain a healthy weight during pregnancy

There are many ways to have a healthy weight gain during pregnancy. While you are 48% likely to gain more than the recommended number of pounds during your pregnancy, you are 21% likely to gain less than the optimal amount of weight.

If you are overweight, you are more likely to overeat and gain too much weight in pregnancy than if you are at a normal weight before becoming pregnant. If you are underweight, you are at greater risk of not gaining enough than if you are normal weight or overweight to begin with.

How can you avoid falling into the trap of gaining too much weight during your pregnancy? There are some tricks to staying within the guidelines:

  • Remain active unless your healthcare provider says otherwise.
  • Engage in aerobic activity. This includes walking, swimming, running, and bicycling. Remember that aerobic activity lasting more than 30 minutes at a time will help you burn fat stores rather than the sugar (glucose) you and your baby need.
  • Eat balanced meals that greatly favor fruits, vegetables, and whole grains.
  • Never drink alcoholic beverages. Alcohol is bad for your baby’s overall development and contains calories without any beneficial nutrients.
  • Avoid drinking your calories. Drinks such as sodas, energy drinks, or lots of fruit juices offer very little except calories.
  • Eat foods high in fiber, such as whole grains, raw vegetables, and whole fruits. Fiber is not absorbed but will help prevent constipation and encourage regular eating.
  • Track calories if needed. If you don’t want to track everything, you can remember the calories in many of your favorite foods to help you make lower-calorie alternatives.
  • Avoid junk foods that are often energy-dense without being nutrient-dense. If you eat a snack-sized bag of potato chips, you will quickly eat 275 calories and more than half of the recommended daily sodium intake. As for nutrients, you’ll only gain some vitamin B6, vitamin C, and magnesium.
  • Stay away from processed foods. These are often energy-dense and have preservatives that promote weight gain.
  • Sleep 7 to 8 hours per night. Too little sleep increases your hunger hormone activity and will contribute to more weight gain over time.
  • Don’t diet. Even if you are overweight or find you’ve gained too much in pregnancy, you shouldn’t restrict your food intake but should course-correct by starting to eat healthier.
  • Avoid fasting. You should avoid intermittent fasting during pregnancy and make sure you don’t go over 13 hours without eating, as this can increase the chance of having a preterm baby.

>> Read more: Healthy snacks to eat while pregnant

How working with a prenatal nutritionist can help you gain a healthy amount of weight

There is so much that a prenatal nutritionist can help you with should you use their services before you get pregnant or while you are carrying your baby during pregnancy. The nutritionist can assess your body mass index and your current diet so you can begin to improve your weight and nutritional status before you get pregnant.

Your prenatal nutritionist will help you boost your folate levels even if you aren’t yet pregnant. Folate is strongly recommended before you even become pregnant. The evidence for folate being needed to prevent neural tube deficits (like spina bifida) is so great that you should take a vitamin with 0.4 to 1 mg of folate as you prepare for pregnancy. Your nutritionist can help you choose the supplement you need, if any.

If you need further advice during pregnancy, your nutritionist can help you manage your diet on a week-by-week or monthly basis. The nutritionist can help with specific dietary challenges or pregnancy issues that are best addressed by carefully managing your diet.

Here at Zaya Care, we can help you find a prenatal nutritionist that meets your needs in terms of visit type (online, over the phone, or in-person), insurance accepted, age, and more.

Risks of gaining weight too fast during pregnancy

Remember that the goal during pregnancy is to gain the optimal amount of weight based on your body mass index (BMI) at the time you became pregnant. There are risks in gaining too little and risks of gaining too much.

Your healthcare provider or nutritionist will weigh you during your visits and track your weight gain over time. They do this to help you see when you’ve gained weight too quickly at any time during the pregnancy.

The risks of gaining too little weight in pregnancy include having a baby that weighs too little at birth or one born prematurely. The placenta may become too small to adequately supply nutrients to your baby.

Generally, the baby “steals” calories from you to gain as much as possible, but low birth weight is still possible.

Gaining too much weight during pregnancy is likely to cause a host of possible complications:

  • Gestational diabetes. If you are obese, your risk of type 2 diabetes is higher before pregnancy. When you are pregnant, your risk of gestational diabetes (high blood sugar in pregnancy) is higher if you gain too much weight. Learn about the symptoms of gestational diabetes here.
  • Challenges with the birth. If you gain weight, so will your baby. Between your baby being larger and your birth passage being smaller (from excess fatty tissue in the pelvis), your baby is more likely to have a tight fit during the birth process. A challenging birth is risky for your baby, too, with issues like birth asphyxia or birth injury more common if your baby is too large for the birth canal.
  • Preeclampsia or high blood pressure. Weight gain is linked to preeclampsia in pregnancy. In this disorder, you’ll have high blood pressure and protein in the urine that can greatly harm you and your baby if left untreated. High blood pressure alone is risky during pregnancy for similar reasons. Learn more about managing high blood pressure during pregnancy with your diet here.
  • Day-to-day discomfort. Being pregnant is hard on the bones, joints, and muscles as you carry around more baby weight. If you add more weight to your own body, you’ll have even more discomfort in these areas.
  • More challenging ultrasound determinations. If you have an excess thickness between your baby and your skin from fatty tissue around your waist, the ultrasound technician will not be able to accurately assess your baby’s health.
  • Premature birth. If you develop preeclampsia or have issues with high blood pressure, you increase the chances of having a premature baby.

We asked Natasha Eziquiel-Shriro, RDN, if there’s a certain point when women should be concerned that they are gaining too much weight during pregnancy. Here’s what she had to say:

The weight guidelines are meant to give us a sense of when to be concerned. But keep in mind that a person’s health history, food habits, and lifestyle often tell us more than statistics.

Putting on weight quickly in early pregnancy may send up an alarm for your doctor. But was this because someone who typically didn’t eat enough improved their mealtime habits? Or were they really overdoing it with processed foods and not paying attention to balance?

Just looking at the number on the scale compared to weight gain recommendations might miss something important. A prenatal nutritionist can help you feel more confident about the meaning of your pregnancy weight changes.

Gaining weight during pregnancy fast FAQs

Why am I gaining weight so fast during pregnancy?
Fluid overload and constipation are the two main causes of rapid weight gain in pregnancy. If these, fluid overload has the greatest chance of causing excessive weight gain. Look to see if your face is puffy or whether there is fluid around your feet or ankles. If you are in your third trimester and have symptoms of preeclampsia (headaches, irritability, blurry vision, or nausea/vomiting), you need to consult with your healthcare provider as soon as possible.

Is it possible to not gain weight during pregnancy?
Some women do not gain weight during pregnancy, particularly if they’ve lost a lot of weight from nausea and vomiting in the first trimester. Generally, the appetite improves by the 12th week of pregnancy, but weight gain may not make up for the initial losses. This isn’t a guarantee of health problems for you or your baby, but you should stay in close contact with your healthcare provider if you’re not gaining weight.

Can I slow pregnancy weight gain?
Remember that dieting is not recommended during pregnancy. You run the risk of eating too few healthy nutrients if you do this. Instead, increase your physical activity and reduce snacking on calorie-dense foods to allow for a slow-down in weight if you’re gaining more than the recommended amount. Other than that, you can make a postpartum weight loss plan so you can get back to a weight you are happy with.

Why am I gaining so much weight in my legs during pregnancy?
All women gain excess fluid weight during late pregnancy. However, it is generally minor. Things that cause more fluid to build up around the lower body include obesity, hot weather, standing a lot, and eating too much salt. Preeclampsia can also cause this problem, so make sure your provider knows you are gaining fluid weight.

Why am I gaining so much weight in my buttocks during pregnancy?
Your buttocks can gain in size if you have fat stores there or if your fluid gain is large. If you have fat stored on your buttocks already, this area will add more during pregnancy. In addition, pregnancy causes your pelvic bones to widen in preparation for childbirth. This can lead to the illusion of larger buttocks.

Why am I gaining so much weight in my arms during pregnancy?
Weight gain in the arms is often due to fluid overload. If you repetitively use your arms at work (typing, labor jobs), you may notice that the fluid gain causes carpal tunnel symptoms (numbness or pain in the hands).

Why am I gaining so much weight in my face during pregnancy?
Facial puffiness is usually caused by fluid overload in pregnancy; however, any time you gain weight, you’ll see some of this in your face. A sudden gain in facial puffiness in just a few days warrants a phone call with your healthcare provider.

Do you gain more weight with a boy or a girl?
On average, boys are born weighing a half pound more than girls; however, this is usually not something you’d notice on the bathroom scale. You shouldn’t expect to gain any more appreciable weight when carrying a boy versus a girl.

What trimester do you gain the most weight in?
Remember that you shouldn’t gain much weight in the first trimester. In the second trimester, weight gain is generally steady and predictable. The third trimester’s weight gain shouldn’t be more than the second trimester; however, it is often in the third trimester if you gain excess fluid. This difference in fluid weight gain could be noticeable.

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Healthy mom, healthy baby: Get support from a prenatal dietitian

90% of Zaya Care patients pay $0 for one-on-one counseling with a Registered Dietitan

Christine Traxler MD is a family physician, lifelong writer, and author with a special interest in mental health, women’s healthcare, and the physical after-effects of psychological trauma. As a contributing writer and editor for numerous organizations, she brings a holistic focus to her work that emphasizes healing and wellness through daily self-care, connecting with others, and setting stepwise goals toward achieving more balanced and authentic lives.