How Much Weight Does a Baby Gain in the Third Trimester?

Your baby will grow and gain weight throughout your entire pregnancy, but he will significantly increase in size only during the last trimester. Even during the last month of pregnancy, your baby will rapidly gain weight, according to the American Congress of Obstetricians and Gynecologists. Your health care provider can determine if your baby is growing and developing properly.

A pregnant woman standing in front of a crib. (Image: ColorBlind Images/Blend Images/Getty Images)

Growth During the Third Trimester

The third trimester of pregnancy brings about rapid development of your unborn baby. The beginning of the seventh month also marks the third trimester. The seventh month of pregnancy typically begins at week 27, according to KidsHealth. Most pregnancies typically last 40 weeks, but babies can be safely born, if the mother goes into active labor, at around 38 weeks. While some babies are born a couple of weeks early, they can also be a couple of weeks late, according to KidsHealth. Your actual due date is just an estimation that is based on your last menstrual period, or LMP.

Size During the Third Trimester

At the beginning of the third trimester, your baby will weigh approximately 2 to 2 1/2 pounds. His weight will almost double in the eighth month of pregnancy to approximately 5 pounds. In your final month of pregnancy, your baby will gain around 1/2 pound per week, according to the American Congress of Obstetricians and Gynecologists. By the time he's ready to meet you and his new family, his weight can range from 6 to 9 pounds.

What This Means for You

Because your baby is gaining weight rapidly, your body will require more calories to nourish you and the baby. The American Pregnancy Association recommends that you consume approximately 2,400 calories per day during this trimester. Depending upon your pre-pregnancy weight and how much weight you've gained throughout your pregnancy, your doctor may recommend more calories -- or fewer calories. Always consult your physician before making any changes to your diet.

Misconceptions About Pregnancy Weight Gain

While you are eating for two, your diet should not consist of unhealthy foods. Your baby needs special nutrients and vitamins to properly grow, according to the American Pregnancy Association. If you were of a normal weight range when you became pregnant, your target weight gain should range between 25 to 35 pounds. If you were underweight, your weight gain should range from 28 to 40 pounds. If you were overweight when you became pregnant, your weight gain should range from 15 to 25 pounds. Women who were obese at the beginning of pregnancy should aim to gain only 11 to 20 pounds during pregnancy.

Additional Considerations

Keep all scheduled prenatal visits to ensure that your baby is growing and developing properly. If your doctor feels that your baby isn't developing properly, he may order special tests such as ultrasounds. Your doctor will also monitor your weight as well as the baby's weight. Although rapid weight gain is common during the final months of pregnancy, excessive weight gain can indicate potential problems such as gestational diabetes.

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