I hope this helps, I looked on IVillage . . .
"I am now 37 weeks pregnant with my fifth baby. Yesterday, my midwife said the baby's head is four fifths engaged. With the second, third and fourth babies, the head was free almost until the last day. Does this mean I may produce early?
To find out if your baby's head is engaging into the pelvis, the midwife feels how much of your baby's head is lying above your pubic bone. The way in which a midwife records engagement can be a bit confusing if you're not a midwife. If she can feel four fifths of the baby's head, she writes down 'four fifths', but this actually means that your baby is only one fifth engaged.
If she can feel two fifths of the head above the pubic bone, the baby is three fifths engaged. If she can feel one fifth of the baby's head, she writes down 'one fifth' and the baby is four fifths engaged. If she can't feel the baby's head at all, the baby would be fully engaged.
As it happens, when you are pregnant with a second or subsequent baby, it is quite common not to engage until the last minute. I can't say for sure, but I think it's most likely that you will go into labour at around the same time, perhaps a day or two earlier, as you did with your previous pregnancies"