Reviewed April 2014, next review April 2017

Explaining premature birth - risks and causes

Finding out the gestational age

The age of your baby on his day of birth is known as his gestational age. It is an important way for his healthcare team to assess his needs.

Many babies born early go on to lead healthy lives, but they are more at risk of complications and other health problems.

Because of the risks, the healthcare team needs to assess each baby's gestational age as accurately as possible to make sure they receive the right care. However, working out exactly when a baby was conceived is not always straightforward.

Finding out your baby's gestational age

Unless you had assisted conception, such as in vitro fertilisation (IVF), you may not know exactly what date you conceived, so the date of the first day of your last period is generally used as an estimate.

For this to be completely accurate, you need to remember the dates of your last period, have a regular 28-day cycle, and have ovulated (produced an egg) half way through this cycle. As this does not always happen, the team will use the results of your ultrasound scans to get the most accurate date possible.

When your baby is born, the team will check him over carefully to confirm his gestational age. Some body parts (such as nipples, eyes and genitalia) do not develop fully until quite late in the pregnancy, so the team can look at these physical features to get an indication of his age.

Click here to find out how your baby's gestational age could affect his medical needs at birth.

The causes and problems of premature birth

Your premature baby:

You can also read about


Fraser DM, Cooper MA (2009) Myles Textbook for Midwives (15th edition), London, Churchill

Norman JE, Greer IA (2006) Preterm labour: managing risk in clinical practice, Cambridge University Press


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'When the team told me that I was delivering at 27 weeks, they said, "You must take each day as it comes." And that's what I did. I never thought about getting him home. I just didn't think too far ahead. I always thought everything would be fine - and it was.'