365 Days of Twinipedia - Day 108 | Does 1 placenta mean Identical Twins?

Day One-Hundred and eight of Twinipedia 

Fact #108

Some people have asked us if identical twins share the same placenta and that is how you Know they are identical?  We have written a little about this before but wanted to touch upon it again since we are curious too.

In the past, this is what doctors and scientists believed to be true; one placenta at birth meant meant 1 egg had split which meant the babies were identical twins.  This is not the belief anymore though.

Some identical twins do end up with one placenta shared, while others do not.  It is now understood that this process depends on when the egg splits to form the identical twins.  It is believed that if the egg splits within the first few days of conception, they will have two separate placentas. If the egg splits after the first week, then the identical twins may share one placenta.

So it is all in the timing of the split, not how many eggs it all started with.