MadSci Network: Development

Re: How does the ovum split to form quadruplets?

Date: Tue May 29 13:46:48 2001
Posted By: Stephen A. Butler, Post-doc/Fellow, Obstetrics and Gynaecology, University of New Mexico
Area of science: Development
ID: 989966172.Dv

Hi Leonie

Quadruplets can arise in the same way that twins form, either from 
fertilization of four eggs or one embryo splitting twice. Obviously to 
have four ova present at one time is particularly rare and the most common 
cause of quads is a double split. Of course it is also possible for 3 ova 
to be fertilized and then one splits to give a total of 4, giving two 
identical and 2 non-identical babies; but again this would be quite rare. 
It is not fully understood why an embryo splits but it occurs when the 
casing of the embryo (the Zona Pellucida) splits with the first cellular 
(bastomere) split. Normally these blastomeres split repeatedly within the 
confines of the zona to form one individual. It is really an intact zona 
pellucida which denotes a singular embryo. Eventually the cells fill the 
zona so much that it hatches and releases the blastocyst. At this point 
the cells are so organized (differentiated) that only one fetus can arise 
from them.

Hope this answers your question and keep asking,


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