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Having a small baby

9-minute read

Key facts

  • Most babies who are born with a lower than average birthweight are born healthy.
  • Most babies born between 37 and 42 weeks of pregnancy weigh between 2.5kg and 4kg.
  • Some babies with an estimated fetal weight smaller than the average may be affected by fetal growth restriction.
  • Causes for fetal growth restriction include genetic conditions, health issues such as high blood pressure and diabetes and smoking or drinking alcohol during pregnancy.
  • If you notice a change in fetal movements at any stage during your pregnancy, seek urgent advice from your doctor or midwife.

Why is my baby small?

Most babies born from 37 weeks of pregnancy weigh between 2.5kg and 4kg. However, around 7 in 100 of babies born in Australia are born with a lower than average birthweight for their gestation (weeks of pregnancy), known as being 'small for gestational age' (SGA).

Most babies with a lower than average birth weight are born healthy. In some cases, babies are small due to the size of their parents and their ethnicity.

In other cases, your baby may be small or growing more slowly than expected due to fetal growth restriction (FGR).

What does small for gestational age (SGA) mean?

Small for gestational age is a term that can be used to refer to your baby before birth or when they are born. It is when your baby's birth weight is less than the 10th percentile for their sex and gestational age, or your doctor predicts they will be based on your pregnancy ultrasounds.

What does fetal growth restriction (FGR) mean?

FGR is when your baby is growing at a rate below what is expected in your pregnancy. It indicates that your baby is not reaching its growth potential.

Most commonly, babies with fetal growth restriction are small because the placenta hasn't developed well enough to keep up with the baby's growing needs for nutrients and oxygen. Fetal growth restriction can be associated with a higher rate of pregnancy complications. If your doctor or midwife identifies fetal growth restriction, they may recommend closer monitoring of your pregnancy. This can help identify and address any complications early, both before and after your baby's birth.

What are the risk factors for having a baby with FGR?

Risk factors for having a baby with fetal growth restriction include:

How is my baby's size measured?

During routine antenatal check-ups, your doctor or midwife will use a tape measure to estimate the growth and size of your baby by measuring your abdomen, from your pubic bone to the top of your uterus (fundus). This is known as the 'symphyseal fundal height measurement' (SFH) and gives some indication about your baby's growth during pregnancy.

If you have risk factors for fetal growth restriction, or if your baby has been diagnosed with FGR, your baby's growth may be monitored more closely by ultrasound.

Every pregnancy is unique. Your doctor or midwife will track your baby's growth at each check-up. If there are signs that your baby's growth has slowed, they will talk with you about next steps.

Should I be concerned if my baby is small?

Most small babies will be healthy. However, if your baby has fetal growth restriction, this increases the risk of complications and, sadly, also the risk of stillbirth.

If your baby has FGR or is predicted to be SGA, you will have ongoing assesment and monitoring, including regular ultrasounds and an umbilical artery (UA) Doppler. Your doctor or midwife will monitor you and your baby's health closely to reduce the risk of complications.

If your baby has been diagnosed with FGR, it's especially important to monitor your baby's health by attending scheduled antenatal visits and keeping a close eye on your baby's movements. If you are busy, it can be a good idea to set a reminder on your phone to check in each day with your baby's movements.

If you are concerned about your baby's movements at any stage of your pregnancy, contact your doctor or midwife immediately, or go to your local hospital.

If my baby is small, will I still be able to have a normal birth?

If your baby has been diagnosed with FGR, your doctor or midwife may discuss with you the benefits of birthing your baby before their due date, for example, by inducing labour. Every situation is different; your doctor or midwife will give you advice each step of the way and you can make decisions together.

Generally a baby with fetal growth restriction can still be born via vaginal delivery, but you and your baby may need extra care both during labour and after the birth. This means it's best to give birth somewhere you can access specialist medical services, such as a hospital.

Talk to your doctor or midwife about the best place for you to give birth.

Can I do anything to reduce the risk of having a small baby?

Often there is nothing you can do to prevent a baby being small. But looking after yourself during pregnancy can help reduce the risk of having a baby with fetal growth restriction. You should:

What should I expect if my baby is born with a low birth weight?

If your baby weighs less than 2.5kg at birth, their head may appear to be a lot bigger than the rest of their body.

Some babies with a low birth weight or who are born prematurely may need to be say in the neonatal intensive care unit (NICU) or special care nursery (SCN) for extra monitoring. This may be for a few hours, a few days or sometimes longer.

Babies born with a low birth weight may be more likely to experience:

  • breathing or heart problems
  • low oxygen levels at birth
  • difficulty maintaining body temperature
  • difficulty feeding and gaining weight
  • infections
  • problems with their eyes and vision

These conditions are more likely to happen in premature babies and those with fetal growth restriction.

If there are no other complications, most babies born with a low birth weight eventually 'catch up' to their peers. In later life, however, people who were born smaller than average may be more likely to develop health problems such as:

Questions you might want to ask your doctor

Here are some questions you might want to ask your midwife or doctor:

  • What does having a small baby mean for me and the health of my baby?
  • Will I need more regular check-ups during pregnancy? If so, what does this include?
  • How will I know if my baby is well?
  • Will having a small baby affect how and where I can give birth? What are my options?
  • Does having a small baby affect my next pregnancy?
  • Will my baby need extra care after they are born?

Resources and support

Always talk to your doctor or midwife first if you have any concerns about your pregnancy, your own health or the health of your baby.

You can learn about your healthcare rights through the Australian Charter of Healthcare Rights.

You can learn about shared decision making on the Australian Commission on Safety and Quality in Health Care website.

Visit the royal Women's hospital page on Aboriginal and Torres Strait Islander Women — resources, for a list of helpful websites for You and your boorai.

Speak to a maternal child health nurse

Call Pregnancy, Birth and Baby to speak to a maternal child health nurse on 1800 882 436 or video call. Available 7am to midnight (AET), 7 days a week.

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: November 2023


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