Progression of pregnancy
Pregnancy can be divided into trimesters.
The first trimester starts with the last menstruation and ends at the beginning of the 14th week of pregnancy. During this period, all the major organs and structures, such as the heart and central nervous system, develop. This period is the most sensitive for the development of the foetus.
The second trimester starts at week 14 and ends at week 28 of pregnancy. The foetus is growing rapidly and the senses are developing. You start to feel the first movements of the foetus during the second trimester.
The third trimester starts at week 28 and continues until delivery. During this time, the foetus grows in size and strength and prepares for life after birth. A full-term baby weighs on average 3.5–3.7 kg and is 50–52 cm tall.
You can monitor your foetus’s growth on the home page of the Maisa client portal, where you will receive a weekly update on the size of your foetus. We will also report the results of any tests during your pregnancy, such as glucose tolerance tests, in Maisa.
Things to remember during pregnancy
This list provides information on the stages of foetal development, as well as a checklist of important things to remember during your pregnancy.
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Conception
About two weeks after menstruation.
Keep in mind
- You should start taking a folic acid supplement at this stage at the latest. Recommended dose: 400 micrograms (µg) per day.
- Stop using intoxicating substances now, at the latest.
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Weeks 0–4
A two-week-old embryo is the size of a pinhead.
Keep in mind
- Eat a varied diet, taking the prenatal dietary recommendations into account.
- When using medication during pregnancy, check the instructions for use with your pharmacist or the teratology information service.
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Weeks 5–8
The foetus is approximately 1.5 cm long and has small arm and leg buds.
The heart, nose, ears and eyelids, nervous system, spine and umbilical cord begin to develop.
Keep in mind
- You may feel very tired. However, you can continue your daily life as normal, depending on how you feel.
- Get enough rest, spend time outdoors and exercise as much as possible.
- Book an appointment for your first check-up at the maternity and child health clinic.
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Weeks 9–12
A 10-week-old foetus is about 3 cm long and weighs approximately 20 g.
Keep in mind
- Book an appointment for your first ultrasound screening according to the instructions you received from the maternity and child health clinic. The scan will be carried out by a HUS maternity hospital.
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Weeks 13–16
A 14-week-old foetus is about 9 cm long and weighs approximately 100 g. The uterus is about the size of a clenched fist.
The foetus has a large head, roughly half of its entire length.
The facial features are beginning to develop. Ears and reproductive organs are developing.
Keep in mind
- Nausea and fatigue will usually start to ease at this stage.
- The foetus is actively moving, but you cannot feel these subtle movements yet.
- At the maternity and child health clinic, we start listening to the foetal heartbeat with a doppler during check-ups.
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Weeks 17–20
An 18-week-old foetus is 25–27 cm long and weighs 250–300 g.
At this point, the placenta is almost as big as the foetus. It protects the foetus from harmful substances but cannot filter out everything.
Keep in mind
- The second ultrasound scan (screening) is carried out at around the 20th week of pregnancy.
- You may already start to feel the movements of the foetus.
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Weeks 21–24
A 22-week-old foetus is about 30 cm long and weighs approximately 400–600 g.
The foetus is practising sucking and will often place its thumb in its mouth.
For most of the time, the foetus is asleep, but can be woken up by external noises or vibration.
Keep in mind
- The movements of the foetus become stronger, and you feel them more and more clearly.
- If you feel any Braxton Hicks contractions, you should discuss them at the maternity clinic.
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Weeks 25–28
A 26-week-old foetus is about 35 cm long and weighs approximately one kilo.
The foetus moves a lot, turning around and kicking, and the movements are also visible on top of the abdomen.
Keep in mind
- You can continue to exercise as usual.
- You may feel occasional contractions where your stomach hardens for a few seconds. Avoid extra strain if your uterus contracts easily.
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Weeks 29–32
A 30-week-old foetus is about 40 cm long and weighs approximately 1.5 kg.
Keep in mind
- Your uterus is growing faster, which can affect how you feel.
- You can try using pillows, for example, to help you find a comfortable sleeping position.
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Weeks 33–36
A 34-week-old foetus is about 47 cm long and weighs approximately 2.7 kg.
Its weight is increasing fast. The foetus is moving less than before, because it is running out of room in the uterus.
Most children will turn upside down at this point.
Keep in mind
- Your thoughts may start to turn to the upcoming birth.
- Now is a good time to think about a support person for the birth and the contents of your hospital bag.
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Weeks 37–40
The foetus kicks strongly in the womb.
On average, a baby is born at week 40 of pregnancy; variations of approximately one week are very common.
At birth, most children are 49–52 cm tall and weigh 3–4 kg.
Keep in mind
- Contractions will increase considerably and may already be more painful.
- Call the hospital if you have any pain or bleeding, or if your womb starts to leak amniotic fluid.
- If none of the above happen, you can call the hospital when your contractions are regular.
