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
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.
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 extrauterine life.
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
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
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
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.
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 extrauterine 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
The first trimester of pregnancy covers between weeks 1-13, or
the first three calendar months. For at least half of this time,
you may not even be aware that you are pregnant. The first week of
pregnancy is included in the first trimester, in the time when you
may be having your period, confusing as it sounds. This is because
it is seen as a time marker for when ovulation is most likely to
have occurred. For the majority of women this is somewhere around
14 days from the first day of her last period, though the time
varies depending on the length of each woman's individual
Welcome to your second trimester. All the hard work involved in
making your baby and helping it to form has been done. Its
essential organs and body systems should be in place and ready to
keep growing and maturing. In your second trimester, your baby will
increase its size 3-4 times and will look more and more like the
little person it will become.
You are probably feeling as if you've reached a significant
milestone by this stage. Getting to the start of your third
trimester really is the beginning of the countdown to when you will
be having your baby. Officially, the third trimester relates to the
weeks between 28 - 40 of gestation. There can be a week or two of
variation though, depending on the source.