Many women will experience rapid weight gain during their third trimester. This is because the fetus typically gains the most weight in this time, according to the Office on Women’s Health (OWH).
In this article, learn what to expect during the third trimester, when to see a doctor, and some tips on how to gain weight safely during pregnancy.
Average weight gain during the third trimester
It is not uncommon for a woman to gain weight during the third trimester.
The amount of weight a woman gains during pregnancy depends on several factors, including:
- their pre-pregnancy body mass index (BMI)
- the number of gestations
- physical activity levels
- nutritional habits
The amount of weight a woman might expect to gain during her pregnancy depends on her pre-pregnancy BMI.
The following table contains pregnancy weight gain recommendations, in pounds (Ib), based on BMI from the Centers for Disease Control and Prevention (CDC):
| BMI before pregnancy | Weight gain recommendations for women pregnant with one fetus | Weight gain recommendations for women pregnant with twins |
| <18.5 | 28–40 lb | 50–62 lb |
| 18.5–24.9 | 25–35 lb | 37–54 lb |
| 25–29.9 | 15–25 lb | 31–50 lb |
| ≥30 | 11–20 lb | 25–42 lb |
When to see a doctor
Women who are pregnant should seek immediate medical attention if they experience any of the following symptoms:
- persistent nausea
- multiple episodes of vomiting every day
- sudden swelling of the face and hands after the 20th week of pregnancy, as this may indicate preeclampsia
- chronic fatigue
- shortness of breath
- extreme thirst or hunger
- vaginal spotting or bleeding
- cramping in the abdomen or pelvic region
- increased vaginal discharge
If a woman has concerns about third trimester weight gain, it is important that they speak with a doctor.
The purpose of weight gain
A fetus usually gains the most weight during the third trimester. They will gain an average of 5 lb and grow around 4–6 inches during the third trimester, according to the OWH.
In addition to the weight from the growing fetus, the body also gains weight from:
- the placenta
- amniotic fluid
- breast tissue
- increased blood supply
- a larger uterus
- fat stores for delivery and breastfeeding
Other changes in the third trimester
The following changes and conditions can also occur during the third trimester of pregnancy:
- shortness of breath
- heartburn
- swelling of the feet, ankles, fingers, and face
- hemorrhoids
- swollen or tender breasts
- Braxton–Hicks contractions, which are “false alarms” that are less intense than labor contractions but help the body prepare for it
Tips to gain weight safely
Healthcare providers assist women with gaining weight safely during pregnancy.
Women can expect to gain weight during pregnancy. However, in the United States, roughly 50% of all women exceed the recommended ranges for pregnancy weight gain, according to one 2017 study.
Excessive weight gain during pregnancy can contribute to adverse health effects such as:
Pregnant women can gain weight safely using these following tips:
Work with a healthcare provider
At the start of a pregnancy, a woman’s healthcare provider will determine their weight gain requirements by measuring their BMI.
Healthcare providers will continue to monitor a woman’s weight gain throughout the pregnancy.
Eat a varied diet
Eating a balanced diet will provide vital nutrients, such as carbohydrates, proteins, and fats, that help sustain both the woman and the fetus.
Women can maximize their nutritional intake by consuming a variety of healthful foods and drinks, including:
- fruits and vegetables
- whole grains
- low fat or fat free dairy products
- proteins, such as poultry, beef, and fish
The Office of Disease Prevention and Health Promotion recommend that women who are pregnant eat 8–12 ounces of seafood each week.
However, certain fish and seafood may contain mercury, which can negatively impact the woman’s health and the fetus’s development.
Safe fish and seafood options include:
- cod
- salmon
- canned tuna
- herring
- oysters
- shrimp
- trout
- tilapia
- catfish
Seafood and fish to avoid during pregnancy due to their mercury content include:
- bigeye tuna
- king mackerel
- marlin
- orange roughy
- shark
- swordfish
- tilefish
Choosing seafood from sustainable sources can help ensure that it is of good nutritional quality.
Eat several small meals per day
Finishing large meals may present a challenge for pregnant women. Some, for example, may have trouble eating or keeping food down if they have symptoms such as appetite changes, nausea, and vomiting.
Also, toward the end of a pregnancy, the growing fetus and enlarged uterus can crowd the abdomen, leaving less space for the stomach to expand.
In these cases, women may wish to try eating several small meals throughout the day, which means that the body has less to digest in one sitting. This may help minimize uncomfortable digestive issues such as nausea and heartburn.
Track calories
Tracking calories can help a person meet their daily caloric needs without overeating.
According to the American College of Obstetricians and Gynecologists, women with a BMI in the “normal” range before pregnancy should aim to consume an extra 340 calories per day during their second trimester and an extra 450 calories per day during their third trimester.
Exercise regularly
Regular exercise can improve cardiovascular health during pregnancy.
Exercising regularly can help reduce the risk of complications, such as preeclampsia, preterm birth, and obesity.
Getting regular exercise during pregnancy also offers numerous other benefits, including:
Learn about the best types of exercise during pregnancy here.
In general, women should try to get 150 minutes of aerobic exercise per week. This can include:
- walking
- cycling on a stationary bike
- swimming
- yoga
In this article, learn more general tips for gaining weight safely.
Summary
During the third trimester of pregnancy, women can expect to gain around 0.5 to 1 lb per week. Some ways to gain weight safely during pregnancy include eating a healthful and diverse diet and getting regular exercise.
Women can work with their healthcare team to track their weight gain throughout their pregnancy.