I lost a baby at 21 weeks because of no fluid around the baby what are the chances of this happening again?

Depends on situation: The primary cause of absent fluid is absent or abnormal kidney formation or severe blockage of the outflow tract.Absent kidneys is sporadic & unlikely to recurr, while something like recessive polycystic kidney disease could recurr at a 25%/conception rate. It would be important to find out what condition occurred with that 1st pregnancy & discuss the results with a geneticist.