Knowing when the third trimester begins can make it easier to plan check-ups, practical preparations, and the final part of your pregnancy. In many sources, the third trimester is considered the period that starts around gestational week 27 and lasts until birth, but the exact week indication can vary slightly depending on the calculation method and local guidelines. (Sources are mentioned throughout.)

The third trimester is often stated to begin at week 27 (27+0). This is a common division, also found in health professional reference works. At the same time, you may encounter divisions where the shift is placed around week 28. In practice, this means that you may find that apps, books, or websites show a slightly different "start week" without it changing anything crucial for your pregnancy.

Source: Store medisinske leksikon describes a division where the third trimester begins around week 27. (SML: sml.snl.no)

If you are unsure whether it's week 27 or 28, it's most helpful to base it on the week division your midwife or doctor uses in conversations and in your medical record. Many count in "weeks and days" (e.g., 26+4), and here some will call the last part of week 26 the "end of the second trimester," while others round more loosely.

If you want a simple rule to stick to: count the third trimester from around week 27 until birth, and use your due date as a marker for where you are in the process.

Relevant explanations can also be found in short FAQ formats, for example, at Skagenonline. (skagenonline.dk)

A common division that many pregnant women encounter is:

• 1st trimester: approx. week 0-12
• 2nd trimester: approx. week 13-26
• 3rd trimester: approx. week 27 until birth

This division is primarily used as a practical language to discuss where one is in the pregnancy and which check-ups typically occur when. However, precise timings for scans and appointments follow the healthcare system's plan and your individual situation, not a specific "trimester shift."

Source: SML's descriptions of trimester division and week guides explaining week calculations. (SML: sml.snl.no, Praksisjordemoder: praksisjordemoder.dk)

When discussing weeks in pregnancy, it is typically counted from the first day of the last menstruation. This is why you can be "in week 27" without having been pregnant for exactly 27 weeks measured from conception.

• Check your medical record or your due date from the scan used for dating.
• Use the week indication you get from your midwife or doctor if you see different answers in apps.
• Write down your week and day (e.g., 27+2) if you need to ask about symptoms or appointments.

Praksisjordemoder.dk specifically reviews how weeks and days are typically used in practice. (praksisjordemoder.dk)

As you approach weeks 27-28, it can be helpful to make preparations more concrete. The focus is often on daily comfort, sleep, movement within what feels good, and getting practical matters in order well in advance.

Contact your midwife, doctor, or maternity ward if you experience symptoms that make you uneasy, such as bleeding, a sudden significant change in fetal movements, persistent severe pain, or signs that you may be going into labor prematurely. When in doubt, it is always better to ask once too often than once too little.

As the belly and body change more in the final part of pregnancy, some may benefit from extra support in daily life. For example, a support belt can relieve the abdomen and lower back for some pregnant women, depending on their needs and recommendations from professionals. You can view Support Belts and a specific product like the Maternity Support Belt.