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Pregnancy health centre

Pregnancy week-by-week

What to expect

How an immature egg in an ovary can develop into a baby is a complex process,
so no wonder it takes on average 40 weeks from the first day of the last menstrual period to the birth of a child.

Healthcare professionals sometimes refer to a pregnancy by trimester, referring to
the three stages of the baby's development inside its mother's womb.

First trimester

The first trimester covers the first 3 months of pregnancy, from the start of
week 1 to the end of week 12. This is the most important period in a baby's
development, when its organs and body structure develop.

Second trimester

The second trimester begins with week 13 and continues to the end of
week 27, a time when your baby is growing rapidly in size. During this
period the baby puts in lots of practise using his or her nervous system,
so you should notice the baby moving.

Third trimester

The third trimester begins from the start of week 28 and continues until the
baby's birth. This is a period of weight gain for your baby. Though the baby's
estimated due date is based on 40 weeks, bear in mind that it is completely
normal for babies to be born anywhere between 37 and 42 weeks. Few
babies are born on their estimated due date.

Being pregnant often raises many questions for the mum-to-be, especially if it's the
first time she is carrying a baby. It can be reassuring to know how your baby – and
you – will change through the weeks of pregnancy. While each pregnancy is
different, this week-by-week guide provides general information to help you know
what to expect in the weeks ahead.

Remember that this is only a guide. Depending on the woman, ovulation can occur
a little later or earlier during her menstrual cycle, for example, so how your baby
develops may not fall precisely within the weeks as indicated. While your own baby
may develop at a slightly different pace than given here, the stages will be the same.

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