Fertility clinic's hCG range

Hi, everyone! I just found this group. I'm 5w2d pregnant after IVF with ICSI. I'm concerned because today was my third round of bloodwork. Based on my previous numbers, I was expecting around 7200 today, but it came back 4518. Now, What to Expect When You're Expecting and Americanpregnancy.org both say this is still a normal good number. My clinic's ranges, however, are much higher! Between weeks 5&6 they want to see 10,000 to 100,000! My RE is concerned, and my first sonogram is scheduled for next Monday.