• Question: why is the skull of a baby soo weak ///

    Asked by zmzmzm to Allan, Diva, Harriet, Nathan on 4 Jul 2012.
    • Photo: Nathan Langford

      Nathan Langford answered on 4 Jul 2012:


      Hi zmzmzm,

      One of the reasons why the skull of a baby is so week is that babies grow so quickly, so the head has to be able to expand. Also, most of human’s head growth happens very early. For example, in 9 months in the womb, a baby grows from being just a single cell to being around 45-50 cm long and with a head that’s, say, around 10-12 cm in diameter. But an adults head is only maybe around 20-25 cm in diameter. That means that our heads only grow by about a factor of 2 between when we’re born and when we’re adults (and it only gets slower as time goes on), but it will have grown by 5 or 8 times during the last 6 months of pregnancy. There’s no way it could do that if it were really hard.

      Another interesting fact is that a baby is generally around 4 “heads” long, but an adult is about 8 “heads” long, which shows you how much faster the rest of us grows.

      But there is another, slightly more icky reason why babies skulls are soft – and that’s to protect the mother. As the baby is born, it has to get pushed out through a really small space, and the fact that the baby’s head is soft really helps with this. If you’ve ever seen a really brand newborn baby, you might notice that their heads are a little squashed out of shape from the birth. Because the baby’s head is soft, this generally fixes itself up after a few days.

      All of this is also helped by the fact that a baby’s skull has a few separate pieces, which will gradually fuse together at around (I think) 18 months old.

      Cheers,
      Nathan.

    • Photo: Diva Amon

      Diva Amon answered on 5 Jul 2012:


      Hey zmzmzm,

      Babies need to have soft skulls so that it can bend and change shape to get through the very small space of the mother’s hip bones during birth.

      It is so soft because the skull of a baby is actually in pieces with gaps between. These gaps are called fontanelles and exist between five skull bones. As the child grows, the bones will become stronger (more calcified) and the bones will fuse together to form one skull like what you and I have. It’s thought that this process takes about 18-24 months to occur.

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