When Do You Start Gaining Weight in Pregnancy?

While most people don’t look forward to gaining weight in pregnancy, some weight gain can actually be beneficial for the baby. Here’s what to know. 

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Weight gain is undoubtedly in the back of every expecting mother’s mind.

Some see weight gain as something to be avoided as much as possible, while others may not be bothered by a small amount of weight gain during pregnancy. 

As with most things in life, there is a happy medium.

It’s important to go beyond your pre-pregnancy weight to support your baby’s development, but if you overdo it, you can increase your risk of health problems like gestational diabetes. 

With that in mind, this guide from USA Rx explains what healthy weight gain in pregnancy can look like, and when healthy weight gain is typically expected — it’s not the first trimester as many people think.  

Read on to discover how you can keep a healthy weight during and after pregnancy. 

How Much Weight Should You Gain in Pregnancy?

How many extra pounds you should gain during pregnancy is based on your pre-pregnancy body mass index (BMI).

How many children you carry also impacts your recommended weight gain. After all, baby weight, amniotic fluid, blood volume, and placenta add up quickly when there are two or even three babies developing! 

You can calculate your BMI using a simple online calculator.

The number you get back will tell you if you’re underweight, overweight, or in the normal weight range.

gaining weight in pregnancy

Once you know your BMI, you can use clinical guidelines to guide how much weight you gain and ensure you gain enough weight. 

Here is how much weight gain is healthy based on your BMI:

Single Pregnancy

  • BMI of less than 18.5 (underweight): 28-40 pounds 
  • BMI of 18.5-24.9 (normal): 25-35 pounds
  • BMI of 25-29.9 (overweight): 15-25 pounds
  • BMI of 30+ (obese): 11-20 pounds

Twin Pregnancy 

  • BMI of less than 18.5 (underweight): Consult with your doctor 
  • BMI of 18.5-24.9 (normal): 37-54 pounds
  • BMI of 25-29.9 (overweight): 31-50 pounds
  • BMI of 30+ (obese): 25-42 pounds

When Do You Start Gaining Weight in Pregnancy? 

According to clinical guidelines, you should gain very little weight during the first trimester of your pregnancy — if any. 

Because your baby is so small, you don’t generally need extra calories during the first trimester.

That’s not to say you won’t feel cravings or hunger here and there, however, it’s much more common for women to actually lose weight in this period due to morning sickness and food aversions. 

Generally, you’ll begin to gain weight in the second trimester. Early in this stage, it’s generally beneficial to gain weight to support your baby’s development — of course, when done via a balanced diet and healthy eating.

About one-half to one pound per week until delivery is considered a healthy amount of weight gain starting from week 13 onward. 

What Happens If You Gain Too Much Weight?

If you gain more weight than is recommended for your BMI, you may increase your child's risk for future health problems, such as obesity, high blood pressure, and high blood sugar.

This can also increase their chances of developing chronic illnesses, such as heart disease. 

Even if your child does not develop a chronic illness, gaining too much weight during pregnancy can still impact their health.

For example, one study found that mothers who ate large amounts of junk food during pregnancy were more likely to give birth to children who experienced cravings for foods rich in sugar and fat. 

Your child isn’t the only one affected by pregnancy weight gain. The weight you gain with pregnancy does not naturally disappear after the baby is born.

If you gain more weight than is necessary, you may become overweight or obese, and experience the dozens of health problems associated with being above a healthy weight range.

What Happens If You Gain Too Little Weight?

On the other end of the spectrum is gaining too little weight. 

Some women may be so averse to the idea of weight gain that they will restrict their calories, essentially dieting during pregnancy.

However, this is not recommended since babies need extra energy (i.e. extra calories) for proper development in the second and third trimesters. 

If you gain too little weight during these critical periods, you increase the chances that your baby will be born too early, and essential organs like the lungs, heart, and brain may not yet be fully developed.

This puts them at risk for various disabilities in adulthood and multiple health problems. 

Tips for Healthy Weight Gain During Pregnancy 

Whether it’s always feeling ravenous or not wanting to eat at all, most pregnant women experience a drastic change in appetite that can impact how many calories are consumed, and ultimately lead to weight loss or weight gain. 

Here are some tips that can help ensure weight gain is within a healthy range:

  • One of the easiest ways to prevent excessive weight gain is to not overeat. Your calories should remain about the same in the first trimester because your baby does not require any significant additional energy. In the second trimester, you can increase your calorie intake by about 300 per day and up to 500 calories per day in the third trimester. 
  • Try to stick to a healthy diet containing the recommended amount of whole foods as much as possible. Fresh produce, lean meat, and whole grains can provide you with the nutrients you need to support a healthy pregnancy with a healthy diet. 
  • Avoid eating junk food as much as you can — highly processed, artificial ingredient-heavy, high-in-sugar, high-in-carbs snacks are likely to increase your food cravings as you and your baby remain unnourished. 
  • If your pregnancy is causing you to undereat, try to stick to more calorie-dense foods. Again, avoid junk food, and look for denser foods including sweet fruit, full-fat dairy, nuts, seeds, and avocados. 
  • Ask your healthcare provider for advice on the type of physical activity you can safely perform. Your OB-GYN doctor can help you determine the best form of regular exercise (prenatal yoga is a popular choice!).

In Conclusion 

How much extra weight you should gain during pregnancy depends on your pre-pregnancy BMI and how many children you’re carrying. 

Most weight gain should happen in the second and third trimesters, which is when your baby will benefit from the extra calories the most as they develop some of their most important organs. 

This said, there’s no need to intentionally up your calories in the first trimester, and weight gain will usually happen start week 13 and later. 

References and Sources: 

Calculate Your BMI – Standard BMI Calculator | NHI 

Weight Gain During Pregnancy | CDC 

Nausea and Vomiting of Pregnancy | PMC 

Maternal "Junk Food" Diet During Pregnancy as a Predictor of High Birthweight: Findings From the Healthy Beginnings Trial | NCBI 

Obesity: Risk Factors, Complications, and Strategies for Sustainable Long‐Term Weight Management | PMC 

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