Pregnancy- Week by Week

  • First trimester: Week 1-13
  • Second trimester: Week 14-27
  • Third trimester: Week 28-40

Your pregnancy will be a special experience no matter if you’ve been through it before, or this is your first time. The thought of growing a baby inside your body until it is ready for independent life may sometimes become almost overwhelming. Joy, relief, excitement and fear are common emotions which can come as quickly as they go. Although at first, forty weeks can seem like an eternity, for most women it goes by pretty quickly.

This series is designed to offer you a pregnancy week by week guide and to support you through the next nine months. Bear in mind that you and your baby are individuals and no two pregnancies will be exactly the same. Though you may have a lot in common with other pregnant women, your experiences could be very different from theirs.

When do I start counting?

The average length of pregnancy is around forty weeks, though to deliver two weeks either side of this is still considered normal. Babies take on average, 38 weeks to grow to maturity but because we can’t pinpoint exactly when conception occurs, we count 40 weeks on from the date of the woman’s last period. Two weeks after this starts is when most women are at their most fertile and more likely to have conceived.

Trimesters: What are they?

The first 13 weeks are known as the First Trimester. From week 14 to week 27 is the Second Trimester and from week 28 week to week 40 is known as the third trimester. Some paediatricians’ feel there is actually a 4th trimester but this is more about the baby adapting to the outside world, rather than an extra 3 months being tacked onto the end of pregnancy. This probably comes as a relief to most pregnant women.

Each of the trimesters is marked by a steady progression of changes for both the mother and her baby. These are designed to prepare them both for birth and to help mature the baby to the stage where it is ready for the outside life.

First Trimester: What happens?

For at least half of the first trimester, most women don’t even realize they are pregnant. Even though it doesn’t seem to make sense that we count pregnancy weeks from before conception even happens, it is the only way to estimate when the due date will be. Using a due date calculator (see attached), and counting 40 weeks from the first day of the last period, it is possible to work out with a fair degree of accuracy when the baby is likely to be born. There are no guarantees of course, because often babies make up their own minds about when they want to come into the world.

The first trimester is a time of tremendous development. There is only a window of time, at around 12-24 hours after ovulation when an egg can be fertilized by a single sperm. This normally occurs in the fallopian tube, whilst the lining of the uterus has built up to provide the ideal environment for the fertilized egg to implant. If fertilization doesn’t happen, the endometrial lining of the uterus is shed at the time of the woman’s next period.

From the moment when a sperm and ovum connect, the tiny group of cells sets about developing its own separate and unique identity. The placenta is formed and plays a vital role in supporting the pregnancy week by week and releasing hormones which regulate the baby’s growth.

In this series, we will look at each of the 13 weeks in this important trimester and see that however tiny it is, vital foundations are being laid down to optimize your embryos chances of survival. We will discuss the changes your body is experiencing and how you may feel. We will also look carefully at how your baby is developing.

Second Trimester: What’s going on in there?

By week 12 of pregnancy, the baby is fully formed and appears more like a minute human. Its head is disproportionally large to the rest of its body and the facial features are recognizable. The second trimester is about further maturity of vital body organs and nervous system development.

Throughout the second trimester of pregnancy, week by week the baby develops in size and maturity. By the middle of the second trimester, most women begin to feel their baby’s movements. This is a time when many pregnancy women start to “bloom” and feel more energetic and generally better than they have done for a while. Nausea tends to settle and it is still too early for movement to be restricted.

In this series we will look between weeks 14-27 and see what is happening physically for both you and your baby. How you may be feeling, what you can do to stay healthy and your baby’s stage of development will all be discussed.


Third Trimester: Are we there yet?

By the third trimester, the baby is having regular periods of rest and activity. It frequently changes the way it is lying, kicks and moves to find its own comfortable positions in the uterus. Your baby’s brain and nervous system will be fully formed by now and its lungs are continuing to mature.

For a pregnant mother, this can seem like the longest of the three trimesters. It is often clear she is pregnant and her size a constant reminder of what the future holds. Even simple activity can become tiring, especially if work and caring for other children is a reality. It can’t be hurried though. The baby still needs to be fully supported by its mother and if it is born too early, will require special care.

Over the period of time between weeks 28-40, this series will show how important all of the stages of foetal development are in preparing your baby ready for real life. We will see how pregnancy changes will influence your emotions, your appearance and even your relationships.

We hope that in this pregnancy week by week guide, we are able to help you understand the progression of changes which pregnancy brings.




Any questions/suggestions? Type here!