* create pregnancy interval variable
by caseid: gen     pregint = cmc_preg - cmc_preg[_n+1] 
by caseid: replace pregint = cmc_preg - cmc_preg[_n+2] if cmc_preg == cmc_preg[_n+1] // if a twin
by caseid: replace pregint = cmc_preg - cmc_preg[_n+3] if cmc_preg == cmc_preg[_n+2] // if the third of triplets
by caseid: replace pregint = cmc_preg - cmc_preg[_n+4] if cmc_preg == cmc_preg[_n+3] // if the fourth of quadruplets

* create pregnancy order variable
by caseid: gen     pregord = tot_pregs-pidx97+1
by caseid: replace pregord = pregord[_n+1] if cmc_preg == cmc_preg[_n+1] // if a twin
by caseid: replace pregord = pregord[_n+2] if cmc_preg == cmc_preg[_n+2] // if the third of triplets
by caseid: replace pregord = pregord[_n+3] if cmc_preg == cmc_preg[_n+3] // if the fourth of quadruplets

* create birth order variable
by caseid: gen     birthord = v201-bidx97+1 if bidx97 > 0 // a live birth
by caseid: replace birthord = birthord[_n+1] if bidx97 > 0 & bidx97[_n+1] > 0 & cmc_preg == cmc_preg[_n+1] // if a twin
by caseid: replace birthord = birthord[_n+2] if bidx97 > 0 & bidx97[_n+2] > 0 & cmc_preg == cmc_preg[_n+2] // if the third of triplets
by caseid: replace birthord = birthord[_n+3] if bidx97 > 0 & bidx97[_n+3] > 0 & cmc_preg == cmc_preg[_n+3] // if the fourth of quadruplets