I have multiple blood test results for single pregnancies and wish to select the blood test result that was taken closest to the date at which a condition was diagnosed for each pregnancy (and drop the other results)
Thus I have four variables: Pregnancy ID, date of result, result, date condition diagnosed, e.g.:

Pregnancy ID Date condition diagnosed Result Date of result
1001 01/02/2009 59 30/07/2009
1001 01/02/2009 72 02/02/2009
1001 01/02/2009 94 01/07/2007
1001 01/02/2009 10 01/01/2002

So in the example of PregnancyID 1001 above, I want to keep the result that is 72 and drop the other three.

How would I do this? When writing my syntax I also want to add the caveat that I only want to do this for pregnancies in which there are multiple results. I have already created variable dup so would want to add the condition 'if dup >=1' to the end of my syntax.

Thank you.