Why does ‘selfish behavior’ lead to miscarriage?

In 10 seconds? A new theory trying to explain why most human pregnancies are lost in the first weeks proposes that the reason could be ’selfish chromosomes’ fighting to increase their transmission to the next generation.

Hold on, I’m a bit confused here... Ok, let me explain the basics. While human males produce four equal sperm from one stem cell, females produce only one egg (the others degenerate). This process is called meiosis. During meiosis gametes (aka reproductive cells) acquire only one set of chromosomes (at this stage they are called haploid). And when fertilization happens, the number of chromosomes doubles (representing each parent), and the fertilized egg, the zygote becomes a 'diploid'. Animals have different numbers of chromosomes. For example, mice have 40, monkeys have 48, and humans normally have 46. But often it's not the case with one extra or one missing chromosome. Which results in miscarriage and distress for the parents.