How is HIV transmitted to a baby?

Transmission is the word for when HIV passes from one person to another.

Mother to baby transmission is also known as vertical transmission.

Most vertical transmissions happen near the time of or during labour and delivery (when the baby is being born). Vertical transmission also includes transmission through breastfeeding.

The biggest risk factor for vertical transmission is the mother’s viral load. This is a measure of how much HIV is in your blood.

The main aim of ART is to get viral load to undetectable. This is the same for everyone with HIV. Viral load tests results are in copies per millilitre (copies/ mL). Undetectable viral load is when this gets to less than 50 copies/mL.

When we talk about an undetectable viral load in this guide we mean less than 50. If a mother’s viral load is undetectable when her baby is born – particularly if this has been the case throughout pregnancy – the risk of vertical transmission is almost zero.

Undetectable viral load is particularly important at the time of delivery. Most risk factors for transmission are removed by reducing the amount of HIV in the blood to undetectable.

Practically all risk factors point to one thing: looking after mother’s health.

Some key points to remember:

  • A mother’s health directly relates to the HIV status of the baby.
  • Having an HIV positive father will not affect whether the baby is born HIV positive.
  • The HIV status of your new baby does not relate to the status of your other children.

Last updated: 1 April 2019.