In 2009, for reasons not fully understood, pregnant women became very unwell with the H1N1 outbreak, particularly those in the 3rd trimester. I was pregnant at the time and did considerable research before getting the fluvax.
There were many different opinions amonst doctors but the advice from the Centre for Disease control in Australia and worldwide strongly recommended getting it. I contracted swine flu early in my pregnancy, in the height of the outbreak and it was awful, and scary, there were many pregnant women on ventilators in ICU who had respiratory failure after getting the flu. By the time I was in the third trimester the second peak was occurring and I got the vaccine to protect me the following season as well.
I did not take the decision lightly but it has become more generally accepted in the medical fraternity that pregnant women are at particular risk from flu and should be vaccinated. Perhaps your obstetrician will have some literature supporting his recommendation.
It also depends on your risk. if you were working in a high risk area like education, health care or childcare I think your chances of being exposed are greater and therefore it warrants some consideration.

Good luck with your decision and here's to a happy healthy pregnancy