You and your developing baby: pregnancy stages

By Bupa

Whether you are pregnant for the first time or an experienced mum, every pregnancy will be unique. What is going on inside your growing belly during this time? Here’s your guide on pregnancy stages; on what usually happens to you and your developing baby from day 1 to delivery.

A normal pregnancy lasts between 37 and 42 weeks, usually an average of 40 weeks, with the weeks of pregnancy divided into three pregnancy stages (or trimesters).

First trimester: weeks 1 to 12

What is happening to you?

During the first trimester, pregnancy-related hormone changes can affect your whole body. When you are pregnant, your womb doesn't shed its lining as it normally does at the end of your menstrual cycle, so you won’t have a period. So for some women, a missed period is the first sign of a pregnancy.

As well as a missed period, you might have other early symptoms of pregnancy, including:

  • tender or swollen breasts
  • needing to pass urine more often
  • tiredness due to hormonal changes
  • nausea and vomiting (morning sickness)
  • feeling bloated
  • mood swings
  • food cravings or aversions.

Not all women have all of these symptoms.

What is happening to your baby?

In the first trimester, your baby’s body and organs develop quickly. By the time you are 10 weeks pregnant all your baby’s body parts are present, if not quite fully developed. There will be a heartbeat, and tiny fingernails on tiny hands, and a face with a profile.
Your baby gets nutrients from your blood through the placenta, while waste products from the baby are returned to your circulation to be removed from your body.

By the time you are 12 weeks pregnant your baby is about 60 mm long. At this stage, your baby's forehead grows with the developing brain, the ears are forming, and the eyelids are still sealed shut to protect the developing eyes. The baby is also able to make a fist as its muscles and nerves start to work together.

Second trimester: weeks 13 to 27

What is happening to you?

In the second of the pregnancy stages, the second trimester, your pregnancy will start to show, although exactly when this happens varies from woman to woman.

Any sickness or nausea usually gets better by the time you’re 16 to 20 weeks pregnant. You may get backache, hip pain or pelvic pain because pregnancy hormones cause your ligaments and tendons to relax, and your posture may change as your baby grows.

You may first feel the baby move around 18 to 20 weeks, but this varies between women and may be a few weeks earlier if it's not your first pregnancy. The movements become much more vigorous and obvious as the baby gets bigger and stronger.

What is happening to your baby?

In the second trimester, your baby's organs grow larger and mature, muscles continue to form, and the skeleton starts to harden. The baby’s kidneys start to work and pass small amounts of urine.

By 19 weeks your baby is more active, is able to hear, and is covered in fine hair called lanugo. Your baby now has eyebrows, eyelashes, toenails have formed and unique footprints and fingerprints. By the end of the second trimester, your baby has a chance of surviving if born prematurely, but would need intensive care. If you have a scan at this stage, it's often possible to find out the baby’s gender.

Third trimester: weeks 28 to 40

What is happening to you?

This is the home stretch as many women give birth around 39-40 weeks. Braxton Hicks contractions (practice contractions) can start in the second trimester, but are much more likely in the third. These can be mistaken for labour but the difference is that real labour contractions will continue to occur regularly. Braxton Hicks contractions only last about 25 seconds.

You may find at this time that the extra weight you are carrying can make you tired. You may also get breathless as your expanded womb makes your lung capacity smaller. Some women have trouble finding a comfortable position to sleep in.

As your abdomen and breasts grow, you may get stretch marks. These are harmless and usually fade after the baby is born.

Towards the end of your pregnancy, generally from 37 weeks onwards, your baby ’engages’ by moving into a ‘head down’ position into your pelvis, getting ready for delivery. This can cause pressure on your bladder and you may need to pass urine more often.

What is happening to your baby?

Your baby's lungs mature throughout the third trimester and by 32 weeks your baby is much more likely to survive if born prematurely. Your baby makes breathing movements, even though the lungs don't work properly until birth.

Your baby gets bigger and bigger as it stores fat in preparation for life outside the womb. Your baby loses the lanugo, grows fine hair, their eyes can open and close, and their teeth may start growing under the gums. By the end of 37 weeks the baby is considered full term, and the baby’s organs can function on their own.

Finally… Delivery day!

The cervix will begin to get thinner and softer and open (dilate) to prepare for delivery. You may feel sharp pains as the cervix dilates and the countdown to the birth of your baby begins!

Australian Government Department of Health. Healthdirect. Pregnancy birth and baby [Online] [Accessed Jan 2015] Available from: Office on Women’s Health. US Department of Health and Human Services [Online] [Last updated Sept 2010, accessed Jan 2015] Available from:

© Bupa Australia Pty Ltd January 2015. This information is intended as a guide only and should not be relied on as a substitute for professional medical advice. Bupa Australia Pty Ltd is not liable for loss or damage you suffer arising out of the use of or reliance on the information, except that which cannot be excluded by law. Consult your physician or other medical professional if you have questions.

Note: The views and advice expressed on this blog post are those of the author and are not representative of the Pregnancy Babies & Children's Expo.

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