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
cycle.
Some pregnancy experts talk of gestational age and how this
compares with foetal age. Gestational age is the age of the
pregnancy and weeks since the last period, while foetal age refers
to the actual age of the maturing baby. Throughout this series and
commencing with the first trimester, we will talk about gestational
age because most of the information around pregnancy does this as
well.
how you may feel
By the end of the first trimester most women have had their
pregnancy confirmed. If you haven't made an appointment to see a
midwife or doctor, now is the time to do it. Some of the earliest
signs of pregnancy have already been discussed (Check week 6) but
here are some others:
- Breast changes including tenderness, tingling, increased
sensitivity and a darkening of the areola (the skin around your
nipple).
- Needing to wee more frequently than normal. This is because of
the increased blood volume as well as your uterus placing pressure
on your bladder.
- Feeling tired, not having any energy and wanting to sleep a
lot. You may feel dizzy or light-headed because of the changes in
your blood sugar levels.
- Feeling nauseated, having morning sickness which might not just
be limited to the early part of the day.
- Being moody and easily irritated. You may be a bit tearier and
not as even tempered as you usually are.
- It is very normal to feel anxious about the possibility of
miscarriage. This most commonly occurs in the early weeks which is
why, for most women by the time they progress to the end of their
first trimester; they feel they can relax a bit.
how you may look
- At twelve weeks your uterus will be starting to lift out of
your pelvis and a small bump may be visible in your lower tummy.
This won't be obvious to others, though you may start to show
earlier if you have had a baby before.
- Your breasts may increase a lot in the first trimester and look
bigger than they normally do. Be prepared to buy new bras in a
larger size.
Now we will start to look at each of the 13 weeks in the first
trimester in more detail and what you can expect.
Weekly Development
By the end of each menstrual period, your body prepares to
release another egg in around a fortnight's time. The lining of
your uterus will build up in readiness to nurture the egg in case
it becomes fertilised. If this doesn't happen, the lining will be
shed with your next period.
more about week
1
Conception usually happens in the fallopian tube and although it
is, by any standards a significant moment, there will be no outward
signs that fertilisation has happened. Generally, it takes around
6-12 days for the fertilised egg to travel down the fallopian tube
to the uterus.
more about week
2
Once it has nestled into the wall of the uterus, signals will be
sent to your body to produce more oestrogen and progesterone. These
and other hormones will help sustain the baby throughout your
pregnancy. Some women will have a small bleed as the embryo
implants into the uterine lining.
more about week
3
The placenta has started to form by now and will play a vital
role in producing specific hormones and feeding your baby. By this
stage, the embryo is smaller than a grain of rice but each of its
cells are already programmed to fulfil a specific function.
more about week
4
It is now that a heart beat may be seen on an ultrasound and the
eyes and ears of the embryo are being formed. Small buds of tissue
start appearing on each side and these will eventually become the
limbs.
more about week
5
If you haven't already done a pregnancy test, do one now. By the
time you are six weeks pregnant, the baby can officially be
measured. It is standard practice when measuring a baby through
ultrasound, to measure from their crown to their rump. By week 6 an
average size is 5-6 mm.
more about week
6
You are now officially just over half way through your first
trimester. Your baby has grown to about 10,000 times bigger than it
was when you first conceived. So much of your baby's growth is
concentrated on their brain this week that around 100 new brain
cells are forming every minute.
more about week
7
This week your baby is around 1 centimetre long and can
officially be called a foetus. The valves in your baby's heart are
present and the passages which will help air flow from their throat
to their lungs have formed. Its fingers, toes and lips, eyelids and
legs are becoming more clearly defined.
more about week
8
At this time the mouth and tongue are starting to be formed. The
hands which until now have been webbed, will start to separate into
fingers. On an ultrasound, the foetus can be seen making jerking
movements.
more about week
9
The foetal heat is dividing into four chambers and it can be
heard with an ultrasound Doppler. All of the baby's body organs
have developed. Their brain is still large and the digestive system
is developing.
more about week
10
By now, the foetus' genitals have clearly formed, but it's still
too early to tell whether you will be having a boy or a girl. Tooth
buds are also forming and the eyes are fully developed. Fine hair
covers the body and its facial features are more clearly like those
of a baby.
more about week
11
By now, the foetus is fully formed and all of its vital organs
and nervous system pathways have formed. Until now, the bones have
been soft but from now on they start to harden. The foetus is less
curled up than it was and starts to straighten.
more about week
12
Your Baby is as cute as a peach this week and around the same
size too. Up until this week, their abdominal organs have been
forming outside their skin but now they will start moving back to
where they should be.
more about week
13