The Prader Scale (also called Prader Staging) was developed by Dr. Andrea Prader as a basic method to rate the ‘degree of virilisation’ of human genitals. It is used primarily to determine the genitals in cases of congenital adrenal hyperplasia (CAH) and other Disorders (or Differences) in Sexual Development, with ratings set into five stages.
Recently this rating system has been used to acknowledge the sliding scale of differences in the genitals of babies, with fully female being zero and fully male being six (0-6), not just those afflicted with CAH.
Stages and ratings of the Prader Scale
- Stage 0 – Normal female genitalia.
- Stage 1 – Mildly enlarged clitoris, slightly reduced vaginal opening, usually within normal variations.
- Stage 2 – Abnormal genitalia able to be clearly seen with the naked eye, phallus being intermediate in size, small vaginal opening with separate urethral opening. Posterior labial fusion present.
- Stage 3 – Further enlarged phallus than Stage 2, with single urogenital sinus and nearly complete fusion of the labia.
- Stage 4 – Upon examination, looks more male than female, with an empty scrotum and a normal-sized penis-like phallus, however this structure is not quite as free from the perineum to be pulled onto the abdomen towards the umbilicus. A small urethral/vaginal opening at the base of the shaft/phallus (hypospadias in a male), with an x-ray showing the internal connection with the upper vagina and uterus.
- Stage 5 – This is complete male virilisation – a normally-formed penis is present, with the urethral opening at or near the tip, and the scrotum formed, but empty. The internal organs in the pelvis include, however, normal ovaries and uterus, with the vagina connecting internally with the urethra (as in Stage 4). Babies are not seen to be visibly ambiguous, and are assumed to be normal boys (with undescended testes), however the diagnosis of CAH is not apparent until signs of salt-wasting develop around a week later.
- Stage 6 – Normal male presentation of the penis with normal testes.
What’s normal and what’s not?
Over the course of the development of the Prader Scale, it becomes obvious that there is a range of genital presentation that are outside the scope of ‘normal’. The question was just how far does this extend, and could these ‘abnormalities’ in fact be classified as part of the normal variation in human genitals?
There is some controversy over the Prader Scale grading system, with atypical genitals not necessarily classified as abnormal. These variations are ‘not infrequent’ (according to the Swiss National Advisory Centre for Biomedical Ethics), and they do not require medical treatment nor are they considered pathological.
An Australian Senate Committee report on involuntary sterilisation found that research on ‘adequate’ or ‘normal’ genitals (particularly for women) ‘raised some disturbing questions’, which covered a particular doctor’s specialty and gender.