Having a small baby

Most babies born from 37 weeks of pregnancy weigh between 2.5kg and 4kg. 

When people say a baby is ‘small’, they may mean:

• the baby has a low birth weight (less than 2.5kg at birth), or
• the baby is smaller than expected for their gestational age.

Around 7 in 100 babies born in Australia have a low birth weight, meaning they weigh less than 2.5kg at birth.

Many babies with a low birth weight are born healthy. Sometimes, babies are small because of the size of their parents or their ethnicity.

In other cases, your baby may be growing more slowly than expected due to fetal growth restriction (FGR) but may still be born weighing more than 2.5kg.

What does small for gestational age (SGA) mean?

Some babies are born smaller than expected for their gestation (weeks of pregnancy). This is known as being small for gestational age (SGA).

The term SGA may be used to describe your baby’s growth before birth or as a newborn. It is when your baby's birth weight is less than the 10th percentile compared with other babies of the same sex and gestational age. It can also be based on your pregnancy ultrasound measurements.

What does fetal growth restriction (FGR) mean?

FGR is when your baby is growing more slowly than expected during pregnancy. It means that your baby might not be reaching their full growth potential.

Most commonly, babies with FGR are small because the placenta hasn't developed well enough to meet the baby's growing needs for nutrients and oxygen. FGR is linked to a higher rate of pregnancy complications. If your doctor or midwife identifies FGR, they may recommend closer monitoring. This can help identify and manage complications early, both before and after your baby's birth.

Risk factors for having a baby with FGR include:

• a previous pregnancy resulting in a small baby, pre-eclampsia or stillbirth
• infections that cross the placenta, such as cytomegalovirus (CMV)
• chronic health conditions, such as high blood pressure, kidney disease (Opens in new tab) or diabetes
• severe anaemia or malnutrition
• smoking, drinking alcohol or using other drugs
• a genetic (Opens in new tab) or chromosomal condition in the baby
• a multiple pregnancy (twins, triplets or more)

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. This is known as the symphyseal fundal height measurement (SFH) and gives a guide to your baby's growth during pregnancy.

If you have risk factors for FGR, or if your baby has been diagnosed with FGR, your baby's growth will 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.

Many small babies will be healthy, but if your baby has FGR, this increases the risk of complications or stillbirth.

If your baby has FGR or is predicted to be SGA, you will have ongoing assessment 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 help reduce the risk of complications.

If your baby has been diagnosed with FGR, it's especially important to attend scheduled antenatal visits and keep a close check on your baby's movements. If you are busy, it can be a good idea to set a reminder on your phone to set aside time each day to feel your baby's movements.

If your baby has been diagnosed with FGR, your doctor or midwife may discuss different options for 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 FGR 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 in a hospital where you can access specialist medical services.

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

Often there is nothing you can do to prevent a baby being small. Looking after yourself during pregnancy is always recommended. This includes:

• not smoking
• eat a balanced, healthy diet
• maintain a healthy weight during pregnancy
• avoiding alcohol and other drugs (Opens in new tab)

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

Some babies with a low birth weight or who are born early (premature) may need to stay 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
• a higher risk of infection
• problems with their eyes and vision

These conditions are more likely to happen in premature babies and those with FGR.

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:

• diabetes (Opens in new tab)
• obesity (Opens in new tab)
• heart problems (Opens in new tab)
• high blood pressure (Opens in new tab)

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 my health and the health of my baby?
• Will I need more frequent 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?

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. (Opens in new tab)

You can learn about shared decision making on the Australian Commission on Safety and Quality in Health Care (Opens in new tab) website.

Languages other than English

Safer Baby has a range of resources available (Opens in new tab) in many community languages.

Information for Aboriginal and/or Torres Strait Islander peoples

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

Access You and your boorai (Opens in new tab) for information about pregnancy and caring for your baby.

Strong Women Strong Babies has a diary (Opens in new tab) that gives you information on how to look after yourself and your baby during pregnancy and in the weeks after birth.