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Onset of labour

Definitions of the onset of labour include:

Many women are known to experience what has been termed the "nesting instinct". Women report a spurt of energy shortly before going into labour. Common signs that labour is about to begin may include what is known as lightening, which is the process of the baby moving down from the rib cage with the head of the baby engaging deep in the pelvis. The pregnant woman may then find breathing easier, since her lungs have more room for expansion, but pressure on her bladder may cause more frequent need to void (urinate). Lightening may occur a few weeks or a few hours before labour begins, or even not until labour has begun. Some women also experience an increase in vaginal discharge several days before labour begins when the "mucus plug", a thick plug of mucus that blocks the opening to the uterus, is pushed out into the vagina. The mucus plug may become dislodged days before labour begins or not until the start of labour.

While inside the uterus the baby is enclosed in a fluid-filled membrane called the amniotic sac. Shortly before, at the beginning of, or during labour the sac ruptures. Once the sac ruptures, termed "the water breaks", the baby is at risk for infection and the mother's medical team will assess the need to induce labour if it has not started within the time they believe to be safe for the infant.