For many pregnant women, the transition to the third trimester feels like an important milestone: your due date is approaching, and both your body and everyday life may begin to change more noticeably. But when exactly does the third trimester start, and how do you calculate it for your own pregnancy? Here is a practical Danish guide with clear week numbers and help planning the rest of your pregnancy.
When does the third trimester of pregnancy start (week 28)
In Denmark, the third trimester is typically said to start around week 28 of pregnancy and last until birth. This means that when you move from week 27+6 to 28+0 (i.e., when you begin week 28), you are normally considered to be in the third trimester.
Why might the information vary slightly?
Some sources describe the trimester breakdown slightly differently because pregnancy can be calculated in weeks, months, or thirds of a course of approximately 40 weeks. In practice, however, week 28 is the most commonly used “rule of thumb.”
When do you enter the third trimester - how to calculate it
The most accurate way is to use your due date or the date your pregnancy is calculated from as a starting point. Remember that the due date may be adjusted along the way.
Quick method (without a calculator)
- Find your current week of pregnancy (e.g., in your app or maternity record).
- When your week changes to 28+0, you are generally in the third trimester.
If you are unsure about the week number
If your dates change along the way, or you are unsure which calculation applies to you, use the most recent date you have received as a starting point. It is completely normal for adjustments to be made early in the pregnancy.
The third trimester week by week - what does week 28 to birth mean in practice?
The third trimester covers the final part of the pregnancy, during which the baby grows quickly, and you often feel more heaviness, fatigue, and a greater need for breaks in everyday life. Many also find that the calendar feels more pressing and that there is more focus on preparing for birth and the time after.
Practical planning in the third trimester
- Keep track of your appointments in the coming weeks.
- Prepare questions gradually (movement, sleep, comfort, concerns).
- Think in terms of small, concrete preparations rather than trying to do everything at once (e.g., washing baby clothes, making arrangements for help, transport to birth).
If you notice fewer movements or a leak of fluid during this time, seek advice immediately.
Due date calculators and dates - why the trimester transition may feel “fluid”
Many use a due date calculator or pregnancy app, but it is important to remember that calculations are only guidelines. A due date is an estimate, and birth can occur both before and after.
How to use the calculation effectively
- Use the week number to plan (appointments, parental leave, practical shopping).
- Use your body as a guide in everyday life: slow down when you need to.
- Speak up well in advance if you have special needs or concerns late in the pregnancy.
Relevant products for comfort in the third trimester (optional)
As your belly gets heavier in the third trimester, some may benefit from extra support in everyday life. An adjustable maternity support belt can relieve pressure on your belly and lower back during activity, if it feels comfortable for you.