What does pregnant mean to you?

Medically, we measure how far along we are in a pregnancy by reporting the number of weeks since your last period (has nothing to do with when conception or implantation happen, interestingly). Based on this confusing logic, we are all almost 4 weeks pregnant at the end of each cycle, even if we have engaged in no sexual activity at all.

With that confusing bit of data out there, we start producing HCG, the pregnancy hormone, after implantation, but fertization happens days before implantation (but is not currently measurable with urine or blood tests). Then, there is the possibility for a chemical pregnancy or an early miscarriage. My question is, at what point do you consider yourself truly pregnant and not just able to get a positive test? When do you feel you are far enough along to allow yourself to fully prepare for motherhood and not just hope and possibility? When do you let your guard down and fully accept that you will have a child?

As a devout atheist, I would prefer if you leave God out of the conversation. I am not asking about opinions on the existence of a soul or when personhood begins. While I respect religious beliefs other than my own, that is not the nature of my question. I guess I am more asking when you feel you are far enough along to safely assume the pregnancy is likely to lead to a birth and it is okay to start planning for this outcome as a likely situation, rather than a possible situation.