How do viruses get passed to unborn babies?

Inside the womb, the blood supply of a mother and her fetus is linked. This means that not only do nutrients and oxygen pass to the baby, but so do both viruses and the antibodies to fight them.

If you become infected with most viruses - such as flu and chickenpox - during pregnancy, then they can be passed to your baby. Depending on your own natural immunities, the stage of development of the fetus, and the type of virus, this can sometimes be nothing to worry about, or may potentially have more serious effects.

Certain treatments are available to help try to prevent viruses being passed to the baby. If a mother carrying the hepatitis B virus has her baby immunized in the first few hours after birth, it may not develop the infection. Caesarean section or treatment with an antiviral medicine (aciclovir) may prevent the herpes simplex virus from being passed on to the baby of a pregnant woman who has genital herpes lesions.