HCG Doubling Slowed after 1200?

Joy
Question for all previously pregnant ladies out there re HCG levels, a bit worried. Anyone else experience slowed doubling of HCG after 1200? My levels are as follows: 8/5 10 am: 1328/8 10 am: 503 (38.8 hr double)8/10 10 am: 1135 (40.88 hr double)8/12 10 am: 1922 (63.6 hr double) Is there truth in the fact that after 1200 levels should double every 72-96 hours?So appreciate the advise.