I am being treated for a stage 1C mucinous ovarian adenocarcinoma (C by default as removed by keyhole surgery when believed to be benign, so already damaged when sent to lab, they tell me it was likely a 1A before surgery).

Removed last June as a seemingly innocent cyst, diagnosed on post surgery pathology.

Full robotic hysterectomy followed and pathology clear from that. 

2 clear CT (one prior to surgery that included virtual colonoscopy) and 1 after hysterectomy as staging / baseline. 

Currently receiving adjuvant chemotherapy (Carboplatin) about to have cycle 4 on Friday.

Until today, all has been positive, results wise. However, I've seen my consultant today and on my bloods from my last cycle, my CA-19 level has changed from 37 (where it has been consistently since the first time it was tested on the day I was diagnosed last July - which was 7 weeks after the ovary was removed) to 39. Obviously my "usual" 37 is the upper limit on what is classed as "normal"  but it has been consistent for me post surgery (pre surgery levels not known). I am now terrified. My consultant says she is not concerned and for me not to panic as it's a small increase and all my scans have been clear and that's more important. But my last scan was the end of November so that could have changed I'm guessing!! She has told me that they do see fluctuations in blood result levels. 
As far as I know, all other markers are normal.

Does/can the CA-19 level fluctuate innocently in a person who is currently believed cancer free? I know it goes up and down according to how well a treatment is working in someone with a known existing tumour, but does it change in a "healthy" individual? I suppose I'm hoping that just because my level has sat at 37 all along, does it necessarily mean something bad because it's raised 2 increments? 
 

I'm hoping it's back at 37 next time and not increased again, but I'm so scared it will have done.