Week By Week: Trimesters: What Are They? 7 years ago

Week By Week: Trimesters: What Are They?

You will hear a lot about trimesters during the coming months. It’s simply the term for the three three-month blocks of your pregnancy:

1st Trimester – weeks 1-13

2nd Trimester – 14-27

3rd Trimester – 28-40

The 40 weeks of pregnancy are actually counted from the first day of your last period, so they include up to a fortnight before you actually conceived. A full-term pregnancy can last from 37-42 weeks.


By the end of the first trimester, all of your baby’s organs and body systems will have been developed. However, every pregnancy is unique and babies grow and develop differently, in particular after the first months. Any figures we use are just guidelines. Your baby's length and weight may differ greatly.

You are likely to come across lots of charts comparing the size of your growing baby to pieces of fruit and vegetables. We’ve done the same when it’s applicable, but to be honest we haven’t encountered too many 37 cm swedes or 46 centimetre honeydew melons in Irish supermarkets.

We’ve made some comparisons for you along the way, but it’s probably best to get out the measuring tape and kitchen weighing scales if you want to imagine what your precious cargo looks like from week to week.