My boyfriends ex is pregnant and I was supportive of it until he said he wants to be in the delivery room... I feel its too much temptation to get emotionally involved with her and the intimacy, as that is about her, not nessisarily the baby in the delivery room

What the hell? He wants to be in the room, to see his baby born. This is not about the mother, it is about seeing the birth of your child.

If you keep this attitude up, there will be lots of problems down the road, as he wants to be involved in the child's life. Because the "babies mamma" is always going to be around.

My boyfriends ex is pregnant and I was supportive of it until he said he wants to be in the delivery room...

I'm a little unclear here. Is the child his? If it is his, then you have no choice here as he is entitled to be a part of his child's birth. And any attempts on your part to interfere with his relationship with his child will not go well. I would rather have a boyfriend who wants to be involved in his child.

On the other hand, if the child is not his, then yes, I think his being supportive of his ex's pregnancy to this level goes over the top.

And what if there is 'temptation to be emotionally involved with her' by being present at the birth? (Not that I think there would be) Do you feel that you have a right to prevent him from being there, to order him around like a child? He is an adult. If his actions don't please you, you say how you feel and why, calmly, and only once. If he proceeds with what he wants to do, you make the choice of accepting it or leaving him.

I personally consider his desire to be present an admirable trait, the trait of a loving parent. I would love him more, not get all worried and jealous.
People come as a package. His child's mother will be intertwined in his life in ways that will test you for years to come. Will you staying out of all of it keep him with you? No guarantees - people break up for all sorts of reasons, and break up more often than they stay together.

But you will surely lose him if you try to protect your relationship with things like this from day one.

How far along is the pregnancy?

I can understand your concern. However, if this is his child or he thinks this is his child, then he should be a part of the child's life from the very beginning.

If you trust him, it is all about the child. There may be some shared moments of look at what we created and memories of happier times, but those will be there whether he is in the delivery room or not.

If this is his child, then they haven't been exes for very long and you haven't been a couple for very long. If you care about him and want your relationship to continue, support him through this.

I know you said that you were supportive up to the point of being in the delivery room. But I wonder if you have really thought about after the child is born. Have you fully thought through and understand that he and she will need to work together to raise a healthy, happy, well-adjusted child? Can you step back and be supportive?