How and why does transmission happen?
Despite remarkable achievements in reducing mother-to-child transmission (MTCT), we do not fully understand how it happens. What we do understand, though, is that there are many factors that affect transmission.
Of these, the level of the mother’s viral load is the most important.
MTCT of HIV can happen before, during or after birth. Scientists have found several possible reasons for infection. Besides the mother’s viral load, her low CD4 count and whether she has AIDS illnesses make it more likely.
The exposure of the baby to a mother’s infected blood or other body fluids during pregnancy and delivery, as well as breastfeeding are thought to be how transmission happens. But most transmissions happen during delivery when the baby is being born. More rarely, some transmissions happen during pregnancy before delivery. This is called in utero transmission.
Some terms used in this section
in utero is within the uterus or womb before the onset of labour.
intrapartum means occurring during delivery (labour or child birth).
placenta is a temporary organ that develops in pregnancy and joins the mother and foetus. The placenta acts as a filter. It transfers oxygen and nutrients from the mother to the foetus, and takes away carbon dioxide and waste products. The placenta is full of blood vessels. The placenta is expelled from the mother’s body after the baby is born and it is no longer needed. It is sometimes called the afterbirth.
foetoplacental circulation is the blood supply in the foetus and placenta.
foetal membranes are the membranes surrounding the foetus.
maternal-foetal microtransfusions are when small amounts of infected blood from the mother leak from the placenta to the baby during labour (or other disruption of the placenta).
chorioamnionitis is inflammation of the chorion and the amnion, the membranes that surround the foetus. Chorioamnionitis is usually caused by a bacterial infection.
mucosal lining is the moist, inner lining of some organs and body cavities (such as the nose, mouth, vagina, lungs, and stomach). Glands in the mucosa make mucous, a thick, slippery fluid. A mucosal lining is also called a mucous membrane.
gastrointestinal tract is the tube that runs from the mouth to the anus and where we digest our food. The gastrointestinal tract begins with the mouth and then becomes the oesophagus (food pipe), stomach, duodenum, small intestine, large intestine (colon), rectum and, finally, the anus. It is sometimes called the GI tract.