topic Re: calculate weeks between a date and numeric variable in SAS Programming

calculate weeks between a date and numeric variable

jdr1 — Fri, 13 Nov 2020 18:53:07 GMT

I'm working on a birth cohort analysis of a 20 year administrative dataset with moms and babies. I'm attempting to do something easy, but cannot figure out how to define weeks of pregnancy to identify trimester 1, trimester 2, and trimester 3 critical windows of susceptibility. I do not have estimated last menstrual period, but only admission_date (date of hospital delivery) and numeric variable for gestation_weeks (20 weeks to 44weeks). How do I work backwards to subtract admission_date from gestation_weeks to then use to define trimester divisions: 1-13 weeks (trimester 1); 14-26 weeks (trimester 2); and >= 27 weeks (trimester 3)?

Re: calculate weeks between a date and numeric variable

SASKiwi — Fri, 13 Nov 2020 22:32:51 GMT

Here's something to get started with:

data _null_;
  admission_date = '14Nov2020'd;
  gestation_weeks = 44;
  conception_date = intnx('WEEK', admission_date, -gestation_weeks, 'B');
  format admission_date conception_date date9.;
  put _all_;
run;

I've defined a conception date, then you can use INTNX again to get trimesters.

Re: calculate weeks between a date and numeric variable

PaigeMiller — Sat, 14 Nov 2020 11:58:13 GMT

In addition using INTNX as above, you could also compute dates like this:

end_of_trimester1 = conception_date + 7*13;

Re: calculate weeks between a date and numeric variable

jdr1 — Sat, 14 Nov 2020 14:48:59 GMT

This worked!!! So, so grateful to SASKiwi for helping me think through this. I was close, just couldn't get there on my own.

Re: calculate weeks between a date and numeric variable

jdr1 — Sat, 14 Nov 2020 14:50:12 GMT

This is very helpful! And helps me get all the way through the calculation. With sincere gratitude!