I've never heard of the copper iud allowing fertilization.

post partum depression is caused by the loss of pregnancy hormones in the body. You never got any pregnancy hormones because you never had implantation. I doubt you ever even had fertilization, much less implantation.

It is possible for an egg to fertilize . But an iud will prevent impantation. This is what I was told by my doctor at the time of insertion.

But are you saying there are no pregnancy hormones untill after implantation? That would answer my question.

Yes, that's what I'm saying Initial pregnancy hormones are emitted by the fertilized egg as it implants and tells the mother's body "don't kill me, I'm not a foreign object!".

yeah eiri is right. You don't get pregnancy hormones BEFORE implantation. That is why implantation is the official and medically approved start of of pregnancy and NOT fertilization. Anyways, contrary to the popular myth, the copper DOES prevent fertilization by acting as a spermicide to kill the sperm before it even reaches the egg. Actually preventing fertilization is the main mechanism of the IUD. However, in rare cases, when the egg was fertilized, the IUD also acts by preventing implantation and thus, preventing pregnancy to occur.

Thank you both for your helpful responses