Is it ok to be late with my 4th PRP treatment?

Hello,
Yes, there won't be a problem. You can get it done every 2 months as well, it will still show its benefits

I personally like monthly for the persistent stimulation, but if you're late in getting the 4th treatment, you should be fine. I usually advise a series of 3 treatments and then one treatment annually. If you are seeing results, keep it up!Best, Dr. Anil Shah

You're very likely in very good shape. There is no single protocol recognized by the medical community as being the best intervals for treatments. 
Experienced medical professionals in PRP hair regeneration largely go with what has worked for them in a given patient. Nonetheless, being a week or two late with your 4th treatment will most likely have a negligible adverse effect if any at all.    
Wishing you a successful outcome!
Warmly,
Arbella Sarkis, MD

There is no international consensus as to the proper timing of PRP treatments for the hair. Some argue that one treatment is enough. Many recommend 3 treatments spaced between one and two months apart and then maintenance treatments after that. It sounds like you've already done 3 treatments one month apart and therefore I don't believe being late for your fourth treatment will make a big difference. 

Thank you for your question! I have treated thousands of people with PRP and have found that many factors affect the timing of treatment. The first is the preparation used.  I recommend 5-6x platelet concentration.  Most clinics are using much less which is why I think they recommend so many treatments. I find that with 5-6x platelet concentration that PRP effects peak between 12 and 18 months and can last up to five years.  I have treated patients who are five years out and have never had to have another treatment.  I also have patients that prefer to have treatment once a year just to be sure they are always on top of it. Follow up is the most important factor to determine future treatments. Best of luck!

It is not set in stone as to the time between treatments. However you don’t want too much time to go by to make sure the PRP is not less effective. I would just recommend getting in as soon as possible.