A quick look around any antenatal class is enough to tell you that women at the same stage of pregnancy will sport bumps in a range of shapes and sizes.

More often than not, it's related to the body type of the mother rather than overall weight (if they're tall, their baby can pretty much stand up and do star jumps, while shorter-torsoed mums tend to push bubs out the front).

Big or small, does it really matter? Sometimes, a smaller bump really does relate to a baby that is small for its gestational age, so here are some of the implications if you are considered 'small for dates'.

What does it mean?
'Small for dates' literally means that your baby is smaller than normal for your particular stage of pregnancy.

Measuring your baby
Measuring unborn babies is quite difficult. In the past, maternal weight was used as a guide to the size of your baby, but this is now considered unreliable because a mum-to-be can gain weight even though her baby isn't thriving. Doctors and midwives often feel the top of your uterus as a rough guide to how your baby is growing (see Getting to know your bump), but this can be unreliable because babies have a tendency to move around.

It's only since the introduction of ultrasound that small-for-dates babies have been predicted more reliably as it gives an accurate estimate of your due date and precise measurements of your baby. These measurements are then compared to a fetal growth chart which shows what's normal for your particular stage of pregnancy.

Because it's difficult to determine whether a baby is small for dates, midwives tend to err on the side of caution by referring women to hospital for a scan, but only one third of women who are seen will actually be carrying a small-for-dates baby.

The causes
The reason for a small-for-dates baby is not always obvious, but there are a few well-known causes:

* Placenta problems If a baby is truly small-for-dates, the most likely reason is a problem with the placenta. The placenta is the lifeline between you and your baby and, if it fails, your baby will lose out on food and oxygen in the womb and will not be able to grow at the usual rate. Problems with the placenta can occur if the mum is ill, for example, with high blood pressure or kidney disease. However, in some cases, the placenta simply seems to wear out and stop working before your baby has finished growing in the womb.

* Smoking, drinking and drugs Smoking is still one of the most common causes of poor fetal growth, and heavy drinking and drug abuse also significantly increase your chances of having a small-for-dates baby.

* Fetal problems Sometimes the reasons for poor growth lie with the baby itself, possibly as a result of genetic abnormalities or an infection.

Other factors
The age of the mother seems to have some bearing. If you are under 18 years or over 35 years, you are more likely to have a small-for-dates baby. Statistics also show that women who've had one small-for-dates baby are more at risk of having another. However, if there was a specific reason for your first baby being small, such as smoking or high blood pressure, and that cause has since been removed, then there's every reason to expect that your next baby should be fine.

Your antenatal care
If a baby is suspected of being small-for-dates, there are a number of steps which can be taken to ensure a safe outcome.

Antenatal tests Several tests can check that your baby is healthy:

* An ultrasound scan can show your baby's size and also how much amniotic fluid (the fluid in which your baby floats) there is.

* A Doppler scan can check the blood flow through your placenta and the umbilical cord.

* Your baby's heart will be checked at each antenatal visit.

Induction
If there is any indication that your baby is not getting enough nutrients in the womb to grow, labour may be induced early – depending on your stage of pregnancy – as your baby might have a better chance of thriving in a special care baby unit.

Managed delivery
Even if there is no need for labour to be induced, there is likely to be medical intervention during your delivery. Labour and birth can be very traumatic for tiny babies so a more managed delivery, such as a caesarean or forceps, will probably be necessary. Some small-for-dates babies may need care in a special care baby unit for a while, but most grow quickly into healthy, thriving babies.

Related: Join the M&B Bump Library! Share photos of your bump – whether it was in your first trimester or third – so other mums can see what was 'normal' for you. Go on, click here!

Your stories 'I was asked to stop work and rest'

'A scan at 20 weeks revealed that Jack hadn't grown as much as would be expected, and a further scan at 30 weeks showed no improvement. I was then given a Doppler scan every two weeks to monitor the blood flow in my placenta.

'At 39 weeks Jack's growth had slowed even more, so I was induced. It was a difficult labour as he was so small and couldn't cope with the birth. His heart rate was very low and, when he became distressed, I was given an emergency forceps delivery. Jack weighed only 1.8kg and he spent his first two weeks in a special care baby unit. But he doubled his birth weight at 10 weeks and now his weight is average for his age.

'I am now 31 weeks pregnant with my second baby and the doctors think this one is also small-for-dates. At the 26-week scan a decrease in amniotic fluid was detected, so I was asked to stop work and rest. I was upset to learn I may have the same problem again, but it's easier to deal with because I know more this time.'
Julie Parkin is mum to Jack, two, and 31 weeks pregnant

Related: Don't forget to upload your photos into the M&B Bump Library! We want to show how different bumps can be. Go on, click here!

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