One of your baby’s most important sources of energy is sugar, in particular, a type of sugar called ‘glucose’.

Glucose is carried to every cell in the body by the circulation of blood. Healthy babies keep themselves well supplied with energy by keeping their blood glucose levels within a normal, safe range.

A good supply of food energy, particularly glucose, is important for normal activity, growth and development.

In rare cases, blood glucose levels can fall too low and a baby may become unwell. When a baby is unwell, the blood glucose level should be checked without delay. The concern is that long periods of low blood glucose in a sick baby may cause brain damage.

In the uterus (womb), babies get glucose from their mother through the placenta and umbilical cord. Some glucose is used immediately as energy and some is stored in preparation for birth. Newborn babies are able to make glucose from these stores. In this way, healthy, well-grown babies keep their blood glucose levels normal for the first few days of life and until they are feeding well.

Once a supply of breastmilk is established (usually by the baby’s third day of life), milk becomes the main source of sugar for the baby. The lactose sugar in milk is converted to glucose in the body. In addition to using sugar from milk for activity and growth, your baby will again store sugar to avoid low blood glucose between feeds.

Another name for low blood glucose is ‘hypoglycemia’. In healthy babies, blood glucose levels are lowest at 1 hour to 2 hours of age, while the baby gets used to being outside the womb; in most cases, blood glucose levels will rise after this, using healthy sugar and fat stores.

Small and preterm babies may not have enough stores to keep the blood glucose level up without extra feedings.

In babies whose mothers have diabetes, the hormone imbalance makes them unable to use their glucose stores when they need them and blood sugar may not rise after 1 hour to 2 hours of life. Babies who are large for their gestational age (or ‘large-for-dates’) may have similar difficulties.

The low blood glucose level (or ‘hypoglycemia’) commonly found in newborn babies usually lasts for a few hours or days; once the glucose levels are restored, your baby should not have hypoglycemia at an older age. Very rarely, low blood sugar can be severe or last a long time, in which case, special tests are done to look for unusual causes.

Healthy babies born at full term do not need blood glucose checks. They have enough stored energy to last them until breastfeeding is well-established – usually by the third day of life.

Babies who are not well need blood glucose checks in addition to the tests that are required for their illness.

Some babies are more likely to have low blood glucose in the first few hours or days of life. The following babies need routine glucose checks starting at about 2 hours of age:

• preterm babies born more than three weeks before they are due, including babies who are born at 36 weeks’ gestation or less;

• babies who are small for their gestational age (or ‘small-for-dates’), particularly, if their growth was poor in the last few weeks of pregnancy;

• babies whose mothers had diabetes during or before pregnancy;

• babies who are large for their gestational age (‘large-for-dates’); and

• babies with rare medical conditions that cause low blood glucose.

Blood glucose can be checked with just a few drops of blood, usually taken from your baby’s heel.

If your baby is in one of the above at-risk groups and is well, blood glucose will be checked at 2 hours of age and then again before your baby feeds, about three to five times during the first and second days of life.

Blood glucose is measured in ‘millimoles’ per litre (mmol/L).

Blood glucose levels change with age and are usually lower in newborn babies than in older children and adults.

When babies are just 1 hour to 2 hours old, the normal level is just under 2 mmol/L, but it will rise to adult levels (over 3 mmol/L) within two to three days. In babies who need treatment for low blood glucose or are at risk for low blood glucose, a level over 2.5 mmol/L is preferred.

If a baby is already sick with low blood glucose, especially if low blood glucose lasts for several hours, there may be a risk of long-term problems with development or learning.

The most natural and important way to feed your baby and maintain a normal blood glucose level is early and regular breastfeeding. Talk to your health care provider before you start using breastmilk substitutes (formula or glucose water).

It is important to know if your baby has one of the risk factors for low blood glucose listed above. If you have diabetes, good control throughout your pregnancy and during labour is also important. It is very important not to smoke during pregnancy because babies do not grow well when exposed to tobacco and its byproducts.

Your baby should be examined to check that there is no sign of illness and that the cause of the low glucose level is not serious.

Your baby will need extra feeding if the blood glucose doesn’t rise on its own. The extra feeds may be given as

• extra feeds from the breast;

• extra feeds of expressed breastmilk or formula; or

• extra feeds of glucose water (or ‘dextrose water’).

If extra feeds do not raise the blood glucose level, intravenous treatment (through a needle or ‘canula’) will be needed.

Blood glucose levels in babies usually become normal within 12 hours to 72 hours of birth, especially once a regular feeding pattern is established. The risk of low blood glucose is greatest in the first 12 hours of life in large-for-dates and full-term babies, and up to 36 hours of life in small-for-dates and preterm babies.

It is rare for babies to continue to have difficulty maintaining their blood glucose levels. If this happens beyond 24 hours, speak with your baby’s doctor.