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What is the size of my baby during the 3rd trimester?

Dr. Deborah Raines, MSN
Nursing Specialist

At 28 weeks the fetus weighs about 2.25 pounds and measures about 15 inches in length.

At 30 weeks the fetus weighs about 3 pounds and is about 15-16 inches long. The fetus is gaining about half-a-pound per week at this stage of the pregnancy. This is visible from the increasing size of the pregnant belly. The fetus begins to shed the lanugo of fine hair that was covering the body as a mechanism to maintain warmth.

At 35 week the fetus is about 18-19 inches long and weighs about 5 pounds. Because of the fetus’ increased size, there may be a slight change in activity patterns as the space for fetal flips and total position changes is limited. The main activity for the remainder of the pregnancy is for the fetus to gain weight to provide the fat stores needed to maintain body temperature in the extra uterine environment following birth.

At 36 weeks the fetus weighs about 6 pounds and is about 19 inches long. The fetus is continuing to gain weight at a rate of about one ounce per day.

At the end of the 36th week the pregnancy is considered full-term.

Here are some size highlights for the third trimester of pregnancy:

  • Week 28 - Your child may reach close to fifteen inches measuring from crown to heel and weigh between two and two and a half pounds.
  • Week 29 - Your baby is between 15 and 17 inches long and is between two and a half and three pounds. As your baby grows bigger, you are going to feel more and more kicks and movements.
  • Week 31 - Your baby is nearly 17 inches long. The periods of sleeping versus wakeful movement will begin being more pronounced now.
  • Week 35 - Your baby has developed most all of its physical characteristics and is filling up your uterus like never before. Your baby is most likely around five and a half to six pounds. That's about the weight of a honeydew melon! On top of that, your baby can stretch to more than 18 inches in length.
  • Week 37 - Your baby can weigh anywhere from six to seven pounds and can also reach up to 19 inches in length
  • Week 39 - Your baby is at a good birth length and weight, though this size varies by baby. On average, the baby is between 19 and 21 inches now and about 7.5 pounds or more. Do not worry if your baby is not exactly this size; your doctor will tell you if the baby's size is something to be concerned about.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.