Understanding weight loss during pregnancy

A person's feet on a scale, symbolizing weight loss during pregnancy.
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Created with Nataliia Yermolovych, MD, Obstetrician-Gynecologist

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In a nutshell

Weight loss during pregnancy is relatively common and may happen due to hormonal fluctuations, increased calorie use by the baby, changing eating habits, metabolic rate change, and morning sickness. 

However, significant or prolonged loss may also cause concern and require personalized guidance from your healthcare provider.

When thinking about pregnancy and its effects on a female body, we know that putting on gestational weight is a natural part of the process of preparing for childbirth. While the amount of weight gained may vary significantly from woman to woman based on individual factors, expectant mothers gain between 22 to 28 lbs on average before they give birth.

But, what if instead of adding extra pounds, you notice you’re losing weight?

Losing some weight during pregnancy can happen due to a range of normal and unconcerning reasons. On the other hand, weight loss during pregnancy might also signal some emerging issues.

In this guide, we’ll walk you through the main reasons for weight loss in every trimester to help you understand what is happening to your body and if it’s okay. We will also discuss potential concerns that may indicate the need for a consultation with a doctor.

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Why weight fluctuations happen during pregnancy

Much of the extra weight you put on during pregnancy is because of the baby’s growth. In the first trimester, most women only gain around 2 to 4 pounds, which might be barely noticeable. After week 20, when the baby starts growing fast, you will likely experience faster weight gain.

In addition to the weight that comes from the baby’s growth, your body will also store up some body fluids and fat. This is natural, as it gives your body the right amount of resources to carry and deliver your child. Also, studies confirm that maternal body fat directly affects the amount of fat in breast milk. 

Due to this reason, females with a lower pre-pregnancy body mass index (BMI) might be storing gestational fat to use for feeding their infants, whereas women with a higher initial BMI might use their own reserves to supply fat for milk.

Hormonal changes during pregnancy also affect weight fluctuations and may cause both weight gain and loss. For example, progesterone and prolactin are linked to increased appetite and weight gain, whereas oestradiol has the opposite effect.

As for weight loss during pregnancy, it may happen due to the following factors:

  • Weight before pregnancy and diet. Plus-size expectant mothers may experience natural weight loss when adjusting their diet for a healthy pregnancy. A higher pre-pregnancy BMI can mean that a woman has a reserve of calories in stored fat that will be used to supply the needed nutrients to the fetus. The body will also use more calories to grow a baby. So if there is no increase in calorie consumption during pregnancy, losing some weight would be natural.
  • Morning sickness. The feeling of nausea can make it hard to consume the desired quantity of food during pregnancy, leading to weight loss. Similarly, vomiting can contribute to weight loss even more if you don’t add extra calories to your diet to make up for what you lose. There is also hyperemesis gravidarum—a condition of extreme nausea and vomiting found in some pregnant women, which can cause a rapid loss of over 5% of body weight.
  • Metabolism changes. During pregnancy, most females experience an increase in their basal metabolic rate. In other words, the amount of calories you burn at rest and during activity increases. If you don’t increase calorie intake in this case, you may lose weight.
  • Stress. Other factors that might contribute to weight loss include stress and anxiety. While it’s natural to experience mild stress during pregnancy, excess stress might be linked to unintentional weight loss.

Weight loss in the first trimester

Most women don’t put on much weight during the first trimester. It’s okay to gain 2–4 lbs, but it’s also natural to lose some weight.

If you are wondering “Why am I losing weight during pregnancy 1st trimester?”, in most cases, it’s due to morning sickness.

Most women face morning sickness around 4–7 weeks, and it settles around the end of your first trimester and beginning of the second, though there might be variations. Nausea often curbs your appetite and makes it hard to consume the amount of calories your body needs, while vomiting can cause you to lose your calories.

If you aren’t consuming the calories necessary for the baby’s growth, your body will likely pick up those calories and nutrients from your own fat reserves to make up the deficit. Hence, you may see a lower number on the scales.

👉Find out more: First trimester pregnancy diet: 1 to 3-month pregnancy diet chart and meal plans

Weight loss in the second trimester

The second trimester is when active weight gain typically begins, as your baby starts growing and developing very rapidly. Your appetite might get back to normal and even increase around the time morning sickness fades.

At this stage, you need to understand the deep metabolic changes that happen in your body, as well as your previous BMI and eating habits, to answer the main question of “Why am I losing weight during pregnancy 2nd trimester?”

The basal metabolic rate change might be the first reason. It starts increasing around the end of your first trimester and may double during the second and third trimesters. The metabolism increase is an individual factor affected by the size of the fetus, the mother’s activities, etc. Due to an increased metabolism, it’s generally recommended that expectant mothers increase their daily calorie intake by around 340 calories. If the intake stays the same or reduces, there might be weight loss.

New dietary habits might also cause weight loss. A pregnancy diet should typically consist of lots of fruits, vegetables, starchy food, proteins, and other important nutrients. Switching to such healthy eating habits can make overweight mothers-to-be expend their pre-pregnancy fat reserves to support their baby’s growth, which may lead to weight loss.

Weight concerns in the third trimester

At later phases of the third trimester, females might arrive at the end of their pregnancy-induced weight gain and  experience stabilization or even mild weight loss.

By this time, many women get so accustomed to weight gain that seeing the number on the scales drop may feel confusing and somewhat unsettling, so it’s natural to have an “I’m not gaining weight third trimester” concern.

In fact, maintaining a stable weight or losing some pounds is relatively common at this stage. It’s a signal that your body is getting ready for labor and can be explained by the following reasons:

  • Amniotic fluid. The amount of fluid in the uterus typically decreases during the final days of pregnancy, which causes weight loss.
  • Bowel movements. At the end of the third trimester, some women experience more frequent and loose bowel movements, which reduces the amount of liquid in their body.
  • Urination. It may also become more frequent, as the baby’s head adds more pressure on your bladder. Fluids exit your body at a higher rate and may decrease your weight.
  • Appetite. You might notice it declines due to increasing discomfort and anxiety before labor.
  • Fluid reduction. When the due date is close, your body doesn’t need to store as much fluid as during the pregnancy and might naturally reduce fluid retention. While heightened perspiration can contribute to fluid loss, it is not always confirmed by medical sources as a primary cause. Usually, fluid is lost through other mechanisms, such as a reduction in the volume of amniotic fluid and increased urination.
  • Nesting. The nesting instinct may also contribute to weight loss during the third trimester—a natural desire to create a safe and comfortable environment for your newborn can make you get on the move and burn more calories. However, this claim has limited scientific backing. While “nesting” might encourage increased activity, its impact on weight is minimal and not consistently observed.

While noticing no gain or mild loss is usually okay, it’s important to remember that the third trimester is a critical stage of your pregnancy, and consistent or excessive weight loss might be a negative sign. It’s important to keep an eye on your weight fluctuations and contact your healthcare provider if concerned about losing too much weight.

A pregnant woman holding her belly.
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When to consult a doctor

If you were wondering “Is it normal to lose weight during pregnancy?”, now you see that there are natural and common reasons  your weight might go down in every trimester. If it’s inconsistent and mild, there might be no reason to worry. 

However, consider talking to your healthcare provider on the following occasions:

  • Your weight loss is too swift and consistent;
  • You feel weak and lack energy;
  • You experience adverse effects of weight loss, such as feeling cold or dizzy;
  • You can’t find relief for your nausea or vomiting.

These signs might signal potential complications that should be addressed by a doctor, especially later in your pregnancy. Even if you don’t experience any of these signals but are generally concerned about your weight gain or loss patterns, it might be a good idea to consult a doctor to ensure your and your baby’s safety.

Remember about the importance of regular prenatal check-ups. If you stick to a consistent prenatal care schedule, it will help your doctor track your weight fluctuations, detect any potential issues early on, and provide you with personalized medical guidance for your and your baby’s wellness.

Questions from the Femia community

  • Can I diet to lose weight while pregnant?

    It’s generally not recommended to diet to lose weight during pregnancy. Expectant mothers need to receive extra nutrients and energy to support a healthy baby’s development. Instead of putting effort into losing or maintaining a specific weight, you should aim to develop a healthy and balanced diet that supplies your body with all the elements necessary for your and your baby’s health and safety. If there are any concerns about your diet or weight during pregnancy, consider talking to your healthcare provider. They will help you develop a personalized plan that will help you maintain a healthy weight and ensure that you and your baby receive all the macroelements you need.

  • Why am I not gaining weight despite eating more?

    To many women, seeing no weight gain during pregnancy despite eating more can feel somewhat frustrating and disturbing, but there might be multiple reasons for it. The most common reasons include hormonal changes, increased metabolism, changed dietary habits, and increased caloric expenditure caused by the baby’s growth. Morning sickness might also cause weight loss. To ensure optimal health and give your baby enough support to grow and develop, it’s important to keep an eye on your weight and consult a doctor in case of any concerns.

  • Can losing weight during pregnancy harm the baby?

    Weight loss during pregnancy can be natural. Losing a few pounds is common in the first trimester due to nausea and vomiting. However, weight loss might be more concerning in the second and third trimesters. While it may not always mean harm to the baby, it’s important to see your healthcare provider if there is significant or prolonged weight loss, because it might affect the baby’s health by not providing adequate nutrition for growth. A professional should be able to objectively assess your unique situation and help you stay on the right track with your nutrition and weight gain.

  • Are there specific dietary recommendations for preventing weight loss during pregnancy?

    Yes - sticking to a healthy and balanced diet is the core recommendation for preventing weight loss. A pregnancy diet should focus on nutritious foods rich in vitamins and minerals necessary for the baby’s development. It should include lots of fruits, vegetables, lean proteins, whole grains, and healthy fats. For nausea-induced weight loss, it’s recommended to have small, frequent meals to manage sickness and ensure that you consume enough nutrients. Staying hydrated is important for helping your body function properly, and taking prenatal vitamins can help fill nutritional gaps. If you are facing challenges with proper nutrition or are concerned about your weight, your healthcare provider can offer personalized guidance.

The bottom line

Weight loss during pregnancy is relatively common, though it often feels unsettling for mothers-to-be. Weight fluctuations may happen naturally during pregnancy because of hormonal changes, morning thickness, increased metabolism, and other factors. There also might be individual factors, such as pre-conception BMI and eating habits that can affect your weight patterns.

After reading this guide, you should know more about weight fluctuations and their reasons. Now, you see that these changes can take place in every trimester and do not necessarily mean something bad, though weight loss might be more concerning during the second and third trimesters. In order to make your pregnancy healthy, it’s important to monitor your weight, have regular prenatal check-ups, and turn to your healthcare provider in case of any concerns.

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