[Spoilers PUBLISHED] If Tyrion and Sanda had consummated their marriage.

The sequence of events that placed Sansa in Petyr's grooming hands seems to be as follow:

1- Sansa tells Dontos that the Tyrells are going to marry her to Wyllas.

2- Donto tells Littlefinger who can't allow this. It will be much more difficult for him to get in grubbing hands on Sansa if she's at Highgarden.

3-Littlefinger tells Tywin who marries her to Tyrion. Afterwards the plan continues as before.

4-Olenna poisons Joffrey while Littlefinger makes everything possible to ensure fingers will point to Tyrion (hiring Penny and her brother to perform at the wedding).

He is counting on Tyrion being executed which will make Sansa a widow and free to marry Harry the Heir.

However, marrying her to Tyrion created an extremely possible setback for Petyr's ambitions that only did not come to pass because Tyrion is a better man than many. What if Tyrion and Sansa had consummated their marriage and he had gotten her pregnant?

Suddenly, the heir to Winterfell and the North has a Lannister babe in her belly. What now? Littlefinger can't rush Sansa's marriage to Harry because it is reliant on Sweetrobin dying and even Lysa would have to suspect if her son died as soon as she married Petyr.

So, instead, will he feed Sansa tansy to get rid of it? That seems risky as hell. He has the best example of how it can destroy the reproductive system right there in Lysa.

Third option is wait for the baby to be born and then find some way to get rid of it.