"Donor sibling" is a widely-used phrase to describe any child who shares a biological connection to another child through genetic material donation - such as sperm donation, egg donation, or embryo donation.
Any child that either T or myself give birth to will have donor siblings who are genetically half-siblings. We are planning on using the same donor that T is pregnant with for my own pregnancy in a few years, so our children will also be genetic half-siblings - but for all intensive purposes they're just going to be regular siblings in our book.
Using a sperm (or egg or embryo) donation means that you have a choice: whether you want to put yourself out there to meet these donor siblings, or not. The choice was easy for us to make, because of course we want to be in contact with our kids' donor siblings and their families. We have zero intention of raising our kids to think of their donor sibs as actual brothers or sisters, but we do want them to be aware of their existence. It's a great idea to keep in touch with these other families too, in case of medical conditions as well as just to compare traits and resemblances. We are very much looking forward to seeing other children conceived using the same donor as we used. Also, down the line, we're hoping that if our kids are struggling with having a donor instead of a father, they can talk about their frustrations with other donor siblings who share a link to them.
The other side to the coin is that once that information is out there, there isn't any taking it back. We can't control who else used this donor, and as we all know, sometimes people do crazy or weird or totally insane things. I'm sincerely hoping that there aren't any other families of this donor who qualify as any of the above... and if they are, I can choose not to respond to them or be involved in their lives in any way.
There is a website called the Donor Sibling Registry, and it's international. You have to pay a fee to peruse the boards and to create postings, but people who have used a donor from anywhere in the world all view this website and it can be a great resource to connect with donor sibs. I'm chomping at the bit to register with the DSR, but it's $175 for a lifetime membership and we are still in the first trimester so I'm forcing myself to wait awhile longer.
Our sperm bank has its own sibling registry, just for people who've conceived using sperm from that bank, which of course we're registered with already. It's free, and you can only view others who have reported pregnancies by the same donor as yourself. Up until today, we were the only couple registered with our donor ("Average Joe") - but this morning, someone else showed up on the registry! We knew that our donor had confirmed pregnancies, but several of them were in 2009 and we hadn't heard of any others until us. The person who showed up on the registry today had her baby in June '11. It's reassuring to see another name on the list, we're hoping to see a couple more. But not too many more! According to the bank, our donor still has a lot of vials, so either he was popular at one point and was selling a lot of vials but isn't anymore, or he's still actively donating.
Soon, we are planning on buying another group of vials to put in storage for our next baby in a few years.
Some days, I still am in disbelief that this has even happened.
We're going to have a baby!