39weekks

The average baby is about 20.5 inches / 51 centimetres long from head to toe and weighs approximately 7.5 pounds / 3.4 kilograms at birth, but anywhere between 5 pounds 11.5 ounces and 8 pounds 5.75 ounces / 2.5 and 3.8 kilograms is a healthy range for newborns.

In TV programmes, labour always begins with the waters breaking - in the middle of a crowded room, of course - just before contractions start. If you've been worrying that this scenario will happen to you, you can stop. Membranes rupture in less than 15 per cent of pregnancies and when it does happen, the baby's head tends to act like a cork at the opening of the uterus. (If you lie down, however, you may notice fluid leaking.) You should stay calm - it may be hours before you feel your first contraction - and call your doctor right away. Your body will produce more amniotic fluid until the baby is born, so your carers may suggest you wait at home until contractions are under way or may suggest an induction.

And if the week passes and there's still no baby? Don't panic - only 5 per cent of babies are born on their scheduled due date. Most doctors wait another two weeks before considering a pregnancy overdue. Check out how to cope with being overdue.

• Note: Experts say every baby develops differently - even in utero. These fetal development pages are designed to give a general idea of how a fetus grows in the womb.