• Question: Does more than one sperm ever implant into the woman's egg?

    Asked by julia123yermak to Enda, Jean, Kate, Kev, Tim on 9 Nov 2012.
    • Photo: Jean Bourke

      Jean Bourke answered on 9 Nov 2012:

      This is very very rare and there are safeguards in place to try and prevent it happening. Mostly, if it does happen, the embryo that results isn’t viable (i.e. it can’t survive and dies).

      A few years ago such an embryo appears to have survived and resulted in twins that were brought to the attention of the scientific community. This is incredibly unusual, though I’m sure it has happened before in the history of humans but we didn’t realise. There’s an article in time magazine about it:
      http://www.time.com/time/health/article/0,8599,1603799,00.html
      but I’ll try to summarise.

      The twins that resulted are semi-identical, they have the same DNA from their mother but only share half their father’s DNA. The researchers investigating this are unsure exactly what happened but they are sure that 2 sperm and 1 egg resulted in these 2 children, whether the egg divided in 2 before or after the sperm fertilised it is not certain thought the latter option is more likely. The embryo at some point managed to correct it’s number of chromosomes but the children that resulted are what is termed chimeric. This means that all the cells in their bodies do not have the same DNA (as is normally the case).

    • Photo: Enda O'Connell

      Enda O'Connell answered on 12 Nov 2012:

      Hi @julia123yermak

      That’s a great question, to which I did not know the answer until I read Jean’s excellent answer!

      If this does happen, and it is rare, it is called “polyspermy” and usually does not result in a baby being born.

      One thing I learned recently, reading the book “Pregnancy for Men – the whole 9 months”, is that it is not necessarily the fastest sperm that gets the prize but that it takes dozens of them to break down the protective barrier around the egg before one of them can make it through.

      So like everything in life, it’s all about timing 🙂

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