It cannot be presumed that the six month baby was more cherished than the six week one, and therefore deserves more tears or grieving time. The death of a baby at any age is worth tears and grief. The intensity of the love or the degree of the loss cannot be measured in weeks, months, or even years. Some parents feel the need to place blame on their doctor, on their life style, on each other, or even on themselves. Placing blame is a way of funneling anger.
Anger is a normal emotion.
However, it needs to be dealt with or it can become a source of potential harm to existing relationships or to selfesteem. Yes, sometimes identifying blame is in order and having this information might possibly prevent a future loss. It may be better to simply accept that fact rather than continue to search for something that may never be found. Even if you know who or what is to blame, knowing will not back your baby, nor will it remove the pain. That is the difficult challenge that parents may face.