How do PRP treatments keep hair on your head when the follicles that are missing are genetically predisposed to miniaturization?

Platelet rich plasma (PRP) injections are one method used to stop further hair loss.  In some cases they can actually promote the growth of new hairs.  With androgenetic alopecia the hairs in each follicle begin to miniaturize.  That is the hair that grows is thinner and shorter than in a non-involved follicle.  In addition, normal follicles can have from one to four hairs growing from them.  As hair loss progresses, the follicles begin to only grow one small hair.  The effect of these changes result in the hair thinning and more of the scalp being visible (scalp show).  
Platelets are one of the cells that are found in blood.  The two other cells, red blood cells and white blood cell, act to carry oxygen and fight infections respectively.  Platelets are used to help blood clot but they also have granules within them that contain many different growth factors.  A good analogy to explain what these factors do is to compare them to fertilizing your lawn.  As fertilizer provides nutrients to help grass grow thicker and greener, growth factors help each cell in the body grow and mature to carry out its primary function.  And in the case of certain cells in the hair follicle, to create and grow hairs.
In a PRP procedure a small amount of blood is taken from the patient.  It is then placed into a centrifuge which "spins" the blood and separates it into its different parts.  After that the part that contains most of the platelets is collected and injected into the scalp in the areas of need.  This "bathes" the hair follicle with these growth factors and stimulates cell division and growth.

The growth factors in prp help reduce miniaturization. Prp is effective, but I have a very specific protocol, every 3-4 weeks for 6 months with prp therapy. I also add in progesterone to speed the healing process.  After that the injections are tailored down. You should also be on viviscal and other growth promoting ingredients. Cost will vary. See an expert for a formal evaluation. Best, Dr. Emer

PRP contains growth factors and cytokines. These have the ability to reverse signs of miniaturization. This includes enlarging the blood vessel Supply, decreasing inflammation around the follicle, stimulating stem cells at the hair bulb and bulge, getting hair to transfer from the resting phase to the growing phase and prolonging the growing phase. However, all this presumes that the follicles are still present. In my experience, if the hair has been lost for less than 5 years, the follicles should remain. Find a PRP expert. Ask to see photos.

When prepared correctly, a high density PRP contains a concentration of growth factors and other beneficial factors such as cytokines that override most hair loss issues when hair loss is less than 2 years old. From 3 - 5 years, the abilities of PRP begins to drop off significantly. 
From a look at the photos and your explanation, I'm thinking you have more going on than androgenetic alopecia alone. 
I recommend locating an Integrative of Functional Medicine "MD" that also practices Bio-Identical Hormonal Replacement Therapy. Once they have treated you for a few months, then try the PRP hair regeneration.  I believe your results will be superior if you proceed in this manner.
Wishing you a great outcome.
Warmly,
Arbella Sarkis, MD 

Your photos are not entirely consistent with androgenetic alopecia. It may of course be one of the diagnoses but another diagnosis may be present. I urge you to please see an expert for review before beginning another treatment. Autoimmune hair loss needs to be ruled out here. 

1.PRP prolongs the growth cycle of hair (the anagen phase).  The growth factors injected will nourish the follicles and maximally stimulate them2. If you have had your menstrual period for a month you could have iron deficiency, which also causes hair loss.   See a dermatologist to get this checked. 

Thank you for your question. You are asking how can PRP keep hair in areas where they are genetically predisposed to miniaturization. Through biopsy, you are confirmed to have androgenetic alopecia. You also indicate you have been on spironolactone.
I can certainly give you some guidance about this. I’m a Board Certified Cosmetic Surgeon and Fellowship-trained Oculoplastic Surgeon. I’ve been in practice in Manhattan and Long Island for over 20 years. I’ve been performing hair transplants since I started my practice. I’m also the founder of TrichoStem Hair Regeneration Centers, based on a system we developed that uses extracellular matrix and PRP for non-surgical treatment of pattern hair loss for men and women since 2011. We have patients from around the world who come to see us for this treatment.
You do seem well-versed in pattern loss, and approach it very logically. In my experience, PRP alone does not thicken thinning hair, but it is proven to stimulate short-term hair growth. You are correct in that PRP does need to be continually done. However, experience with patients who had PRP alone done elsewhere has shown that results of PRP are difficult to sustain, even with multiple and ongoing treatments. Patients also don’t have the patience, time, and pain threshold to regularly have scalp injections.
We do things differently in our practice using a PRP combination with extracellular matrix by ACell. Extracellular matrix is the main ingredient of our treatment, and PRP is the activator. Our treatment called Hair Regeneration has shown since 2011 as I was a pioneer of this injection treatment to thicken thinning hair, and stimulate growth from dormant hair follicles that are still viable, but not have been growing hair for a period of less than 5 years. While the cause of female pattern hair loss is not yet determined, and the mechanism of our treatment is not yet quite clear, it does appear to renew a healthy hair growth cycle using a wound healing mechanism. Both PRP and extracellular matrix are wound healing materials. The body naturally has a wound healing response, such as collagen production in healing cuts and burns. With a wound healing response, we have been able to achieve a renewed hair growth cycle, so thinning hair grows back in thicker, and stimulate growth from hair follicles that have not been growing. It sounds theoretical, but for going on 8 years, we have seen thicker scalp coverage and growth in over 99% of our pattern hair loss patients, both men and women. We have achieved this in one treatment session, with sometimes a booster in the second year, to sustain thicker hair growth for 3-5 years, sometimes even longer.
You are also correct that hair is genetically predisposed to thinning in people with pattern hair loss. The Hair Regeneration treatment is not a cure for hair loss, because there is no cure. Pattern hair loss is hardwired into the DNA, so it can’t be cured. However, we can manage hair loss so we can make hair as thick as possible, for as long as possible, so you can sustain thicker hair growth than you would without treatment. Our female Hair Regeneration do not need to use spironolactone or minoxidil, but you may need to repeat the treatment about every 5-6 years or so to keep thicker hair coverage for as long as possible.
You can meet with doctors who perform treatments beyond just PRP. It is important to note that not all PRP+ACell treatments are the same, even though they sound like the same treatment. We customize each treatment based on an algorithm I established that factors gender, current age, age of onset of hair loss, degree of hair loss, and other medical treatments used, like spironolactone in your case. I have found that most practices using PRP+ACell treatments are using the same formulation applied to all degrees of hair loss, in all ages, and perhaps with the same formulation for men and women. I hope you found this information helpful. Thank you for your question.