What does it mean when you recieve a letter from the IRS saying they are conducting a thorough review of my return and what can I do to speed up the process

It simply means they are processing your return.

Unless the IRS requests specific information from you, there is nothing to do on your part.

So  if there  was a problem with my return  they would of informed me via  wmr site when i go into it to check  status  of  my return

Turbo tax users are automatically being flagged.

I have to agree with lee853 that "Turbo tax users are automatically being flagged"

Why are they flagging turbo tax

I have a similar problem. My letter dated March 20 told me to wait 90 days and contact them if I still do not have the refund at that time.

Does anyone have the answer? 

It means that the IRS is looking over your tax return to ensure everything is correct. Once they have completed their review, they will notify you via mail. There is no way to speed this process up. 

You would need to contact the IRS for further assistance regarding this matter as they are the only ones that can look into your account. Their phone number is 800-829-1040. When calling, be sure to have the following:

• Your Social Security Number or Individual Taxpayer Identification Number
• Your filing status (Single, Head of Household, Married Filing Joint, or Married Filing Separate)
• Your prior-year tax return (they may ask you questions from it to verify your identity)
• A copy of the tax return you’re calling about
• Any letters they may have sent you
• Paper and pen to take notes—make sure to write down the day you called and the name and ID number of the agent you spoke to, as well as any instructions or deadlines you were given.

Please note: You may experience a delay, long hold times, or a busy signal when trying to contact them as the IRS lines are extremely busy at this time of year.

@Jlb03