Third Trimester: What to Expect & When It Starts

What Is the Third Trimester?

The third trimester is the final of pregnancy's three stages, running from week 28 until birth, usually around week 40. It is the last stage of the pregnancy trimesters, the framework that divides pregnancy into three ordered stages. The third trimester follows the second and closes the pregnancy at birth. This page explains when the third trimester starts, how many weeks it lasts, what to expect during it, and which nutrients matter most in late pregnancy.

When Does the Third Trimester Start?

The third trimester starts at week 28 of pregnancy. Week 28 is the boundary the Australian Government Department of Health's Clinical Practice Guidelines: Pregnancy Care use to mark the beginning of the final stage. From week 28, pregnancy is in its third and last trimester until birth.

How Many Weeks Is the Third Trimester?

The third trimester lasts about 13 weeks, from week 28 to full term at around week 40. Some pregnancies may continue longer, which extends the third trimester slightly. The stage ends at birth, whenever that falls within the full-term range.

What Happens in the Third Trimester?

The third trimester brings fast fetal growth and the body's preparation for birth. The defining features of the third trimester, recognised in Australian pregnancy care guidance, are listed below:

• Rapid fetal growth: the baby gains most of its birth weight during these weeks.
• Braxton Hicks contractions: irregular practice contractions that prepare the body for labour.
• Preparing for birth: increasing physical readiness as the due date approaches.

These features define the third trimester and mark the final stage of pregnancy.

Which Nutrients Matter Most in the Third Trimester?

DHA and iron are important nutrients in the third trimester of pregnancy. According to the NHMRC Nutrient Reference Values for Australia and New Zealand, DHA and iron remain important through late pregnancy. For detail on DHA at this stage, see the guide to dha in pregnancy. Iron continues to matter in the third trimester and is covered in the iron during pregnancy.

How Does Third-Trimester Nutrition Fit Your Whole Pregnancy?

Third-trimester nutrition is the final stage of a whole-pregnancy nutrition picture that changes from trimester to trimester. The late-pregnancy focus on DHA and iron follows the folate emphasis of early pregnancy and the iron and calcium. Folate, iodine, and vitamin D matter from conception right through to birth. For the complete view of women's nutrition across every stage, see the guide to key nutrients for pregnancy.