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Checking blood glucose in newborn babies

Highlights
  • Healthy full-term babies do not need blood glucose checks. 
  • Blood glucose is checked with just a few drops of blood, usually taken from your baby’s heel.
  • The most natural way to feed your baby and keep a normal blood glucose level is early and frequent breastfeeding. 

What is blood glucose?

Blood glucose is a sugar that moves through the bloodstream and provides energy to all the cells in the body. It is one of your baby’s most important sources of energy.

Babies with normal blood glucose levels have all the energy they need for healthy growth and development. However, in rare cases, blood glucose levels can fall too low and cause a baby to become sick.

Where do babies get glucose?

Babies get glucose through the placenta and umbilical cord while in their mother’s uterus (womb). Some of that glucose is used right away as energy and some is stored for after birth. This stored glucose helps keep your baby’s levels normal for the first few days of life until she is feeding well.

Once mom’s breast milk is established (usually by a baby’s third day of life), it becomes the main source of sugar for your baby. The sugar in milk changes to glucose in the body. When this happens, your baby will also start to store glucose for use between feeds.

Why do some babies have low blood glucose?

  • In healthy full-term babies (babies born after 37 weeks), blood glucose levels are at their lowest 1 to 2 hours after birth. After this, the levels usually start to rise as your baby’s body starts to use healthy sugar and fat stores.
  • Small and preterm (early) babies may not have enough stores to keep the level up without extra feedings. These babies are most at risk for low blood glucose in the first 36 hours of life.
  • Babies whose mothers have diabetes (especially mothers who need insulin or have diabetes that is not well controlled) may have trouble using their glucose stores. The normal rise in blood sugar that takes place after birth may not happen right away.
  • Babies who are large for their gestational age (also called “large-for-dates”) may have the same kind of problem during the first 12 hours of life.

Usually, low blood glucose levels will only last for a few hours, but can last up to 24-72 hours. Once your baby’s levels become normal, he shouldn’t have further problems with hypoglycemia (another name for low blood glucose).

In very rare cases, low blood sugar can be severe or last a long time. If this happens, your doctor will do special tests to look for other causes.

Do all newborn babies need blood glucose checks?

Healthy full-term babies do not need blood glucose checks. They have enough stored energy to last them until breastfeeding is going well. Babies who are not well will need blood glucose checks and other tests.

Some babies are more at risk for low blood glucose. Babies who need routine glucose checks include:

  • Preterm babies born more than 3 weeks before they are due (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.
  • Babies with rare medical conditions that cause low blood glucose.

How is blood glucose checked?

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

If your baby is at-risk (see above) but doing well, blood glucose will be checked around 2 hours of age and then again before your baby feeds. In total, it will be checked about 3 to 5 times during the first and second days of life.

Why is low blood glucose dangerous to babies?

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

What is the normal level of blood glucose in a baby?

Blood glucose is measured in millimoles per litre (mmol/L). Newborn babies should be treated when a single blood glucose test is less than 1.8 mmol/L, or when more than one test shows levels of less than 2.6 mmol/L.

What do I do if my baby has low blood glucose levels?

Your baby will be checked for signs of illness. He will need extra feedings if his levels don’t rise on their own. The extra feeds can be given:

  • from the breast,
  • as expressed breast milk, or
  • as formula.

If the extra feedings don’t raise the blood glucose level or if your baby is not able to feed well, your baby will need intravenous treatment (through a needle or tube inserted into the body). Preterm babies or babies with low birth weight often have an intravenous started when they are born.

How long will blood glucose checks or additional treatments be needed?

Blood glucose levels usually get back to normal within 12 hours to 72 hours (3 days) of birth, especially once your baby is feeding regularly.

It’s rare for full-term babies to continue having trouble with their blood glucose levels. If this happens beyond 24 hours, your baby’s doctor may want to do more tests.

How can I prevent low blood glucose in my baby?

The most natural way to feed your baby and to keep a normal blood glucose level is early and frequent breastfeeding. Talk to your health care provider before you start using breast milk substitutes (formula).

It’s also important to know if your baby is at risk for low blood glucose (see above).

Do not smoke during pregnancy. Babies who are exposed to tobacco don’t grow well.



Reviewed by the following CPS committees:
Fetus and Newborn Committee

Last Updated: December 2013

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