In the movie Match Point by Woody Allen, the character played by Scarlett Johansson, Nola reveals to Chris Wilton (Jonathan Rhys Meyers) she is pregnant and she is not willing to abort the baby. But why didn't the detectives mention anything about this during the investigation of her murder? It was a murder and obviously an autopsy would be conducted. This could be a strong lead to the case. Was she lying to Chris to make him divorce his wife?
I think there are two possible answers to this.
Throughout the story, luck comes into play. Chris got rid of all the jewellery into a river. Just by chance, a one in a million chance, one of the rings doesn't go into the river but instead lands on the pavement. This ring is then pocketed by a drug dealer who is later killed. Since the prime suspect of the police was a drug dealer of some sort, this fit their "picture" of the crime perfectly and they stop investigating, leaving him in the clear.
So that's the sceond way of looking at things. Nola was pregnant, but by pure luck the police never found out, never noticed the bit in the diary with it (assuming it was there), Chris got lucky in that the ring he dropped ended up brilliantly pinning the blame on someone else and he ended up luckily carrying on his normal life, with his little boy.
I don't think there is a right answer, so much as two open possibilities. It really just depends which you prefer.