Can thyroid problems in pregnancy affect weight?

Yes. Both overactive and underactive thyroid can impact weight changes during pregnancy.

Do you gain more weight with a baby boy in pregnancy?

Yes, some studies suggest carrying a male foetus is linked with slightly higher maternal weight gain compared to carrying a female foetus.

Losing Weight During Pregnancy: Causes and When to Worry

Pregnancy is often thought of as a time when your body naturally gains weight, so noticing the scale move the other way can feel confusing or worrying. Your body is going through huge changes, and sometimes these changes can cause a bit of weight loss in the early weeks. Your appetite may shift, or you might become more sensitive to smells, making eating a little tricky.

Is Losing Weight During Pregnancy Safe?

Trying to lose weight on purpose while you are pregnant is not safe. It doesn’t matter what your body size is. During pregnancy, your body needs enough food and nutrients to help your baby grow well. If you cut down on food or go on a diet, you could put yourself and your baby at risk.
For example, intentionally losing weight in pregnancy could increase the risk of having a baby who is too small (known as small for gestational age) or even lead to preterm birth.

Even if you’re overweight or obese, deliberately trying to shed weight in pregnancy isn’t recommended. Instead, the focus should be on healthy eating and staying active.

That said, sometimes weight loss happens without you trying. This is called unintentional weight loss, and it can occur in different stages of pregnancy.

Why You Might Be Losing Weight During Pregnancy in the First Trimester

It’s actually pretty common to lose a little bit of weight in the early weeks of pregnancy, particularly during the first trimester (up to week 12).

These are some reasons why it happens:

Morning sickness: Nausea and vomiting in early pregnancy can make eating feel like a challenge. The nausea might reduce your appetite, and vomiting can mean you’re losing calories. This can cause a small drop in weight.
Fat reserves: If you’re overweight, your body might use stored fat to provide energy for your growing baby. This can make your weight stay the same or even dip a little in the early months.
Healthier habits: Many people start making healthier choices once they find out they’re pregnant. You might swap junk food for more fruits and vegetables, or cut back on fried snacks. Some also begin gentle exercise like walking or stretching. These small lifestyle changes can sometimes lead to weight loss, too.

In most cases, losing a little weight in the first trimester isn’t dangerous.

Weight Loss in the Second or Third Trimester

Losing weight in the second or third trimester is less common and could signal an issue. During these stages, your baby is growing rapidly, and your body is expected to gain weight to support that growth. So if you notice you’re losing weight during pregnancy instead, it’s something you should talk about with your doctor.

Here are a few reasons why this might happen:

Low amniotic fluid: Insufficient amniotic fluid can affect your baby’s growth and might contribute to weight loss.
Poor foetal growth: If your baby isn’t growing as expected, it could lead to a drop in your weight.
Pregnancy-induced hypertension or preeclampsia: These conditions can affect your weight and your baby’s growth.

Not every reason for weight loss in later pregnancy is serious. It's possible that you might be losing water weight after temporary retention.

However, common pregnancy symptoms like nausea, heartburn, bloating, or constipation can also make eating uncomfortable. This means you might eat less and lose weight without realising.

Why Dieting During Pregnancy Isn’t Safe

Pregnancy is not the right time to try losing weight on purpose, no matter what size you are. If you cut back too much on food, your body and your baby may miss out on important nutrients. This can affect your baby’s growth and development.
Strict diets like keto, which cut out most carbohydrates, can be especially risky. When your body doesn’t get enough carbs, it starts burning fat for energy. This creates a state called ketosis. While that might sound harmless, ongoing ketosis during pregnancy can actually harm your baby. Carbohydrates are one of the main fuels your baby needs to grow healthy and strong, so cutting them out isn’t a good idea.

Tips to Manage Weight Loss During Pregnancy

If you notice your weight dropping even though you aren’t trying to lose it, there are simple things you can do to support your health:

If nausea makes it hard to eat large meals, try eating smaller portions every few hours.
Choose foods that give you long-lasting energy and important nutrients. Whole grains, beans, fruits, and vegetables are great options.
Aim for around 8 cups of water a day to stay hydrated.
Eat healthy snacks like nuts, yoghurt, or fruit to boost your calorie intake between meals.
Take the prenatal vitamins your doctor recommends.
Greasy or heavy meals can sometimes trigger nausea. Pay attention to which smells or foods make you feel nauseous and try to stay away from them.
Gentle exercise like walking or prenatal yoga can help maintain stamina and reduce pregnancy discomfort. Just avoid overexertion that could lead to burning too many calories.
Sleep and relaxation are just as important as food. Lack of rest or high stress can lower your appetite and make weight loss worse.

Losing weight during pregnancy can feel a bit worrying. In the first trimester, it’s usually nothing to panic about. Morning sickness, changes in your eating habits, or your body using stored fat can all cause a little weight loss, and most of the time, that’s normal. But if it happens in the second or third trimester, it can sometimes point to problems that need medical attention.
Whether you’re pregnant, a new mom, or navigating postpartum, you don’t have to do it alone. Join our support group to connect, share, and support one another.

FAQs on Pregnant and Losing Weight? Here's Why That Might be Happening

Can thyroid problems in pregnancy affect weight?
Yes. Both overactive and underactive thyroid can impact weight changes during pregnancy.
Do you gain more weight with a baby boy in pregnancy?
Yes, some studies suggest carrying a male foetus is linked with slightly higher maternal weight gain compared to carrying a female foetus.