The appearance may be quite ambiguous, describable as female genitals with a very large clitoris and partially fused labia, or as male genitals with a very small penis, completely open along the midline ("hypospadic"), and empty scrotum. Fertility is variable. Measurement systems for ambiguous genitalia
The orchidometer is a medical instrument to measure the volume of the testicles. It was developed by Swiss pediatric endocrinologist Andrea Prader. The Prader scale and Quigley scale are visual rating systems that measure genital appearance. These measurement systems were satirized in the Phall-O-Meter, created by the (now defunct) Intersex Society of North America. Other signs
In order to help in classification, methods other than a genitalia inspection can be performed. For instance, a karyotype display of a tissue sample may determine which of the causes of intersex is prevalent in the case. Additionally, electrolyte tests, endoscopic exam, ultrasound and hormone stimulation tests can be done. Causes
Intersex can be divided into four categories which are: 46, XX intersex; 46, XY intersex; true gonadal intersex; and complex or undetermined intersex. 46, XX intersex
This condition used to be called "female pseudohermaphroditism". Persons with this condition have female internal genitalia and karyotype (XX) and various degree of external genitalia virilization. External genitalia is masculinized congenitally when female fetus is exposed to excess androgenic environment. Hence, the chromosome of the person is of a woman, the ovaries of a woman, but external genitals that appear like a male. The labia fuse, and the clitoris enlarges to appear like a penis.
Monozygotic twins split into two zygotes at some time very early in the pregnancy. The timing of this separation determines the chorionicity (the number of placentae) and amniocity (the number of sacs) of the pregnancy. Dichorionic twins either never divided (i.e. : were dizygotic) or they divided within the first 4 days. Monoamnionic twins divide after the first week. In very rare cases, twins become conjoined twins. Non-conjoined monozygotic twins form up to day 14 of embryonic development, but when twinning occurs after 14 days, the twins will likely be conjoined. Furthermore, there can be various degrees of shared environment of twins in the womb, potentially leading to pregnancy complications. It is a common misconception that two placentas automatically implies dizygotic twins, but if monozygotic twins separate early enough, the arrangement of sacs and placentas in utero is in fact indistinguishable from that of dizygotic twins. Demographics
A 2006 study has found that insulin-like growth factor present in dairy products may increase the chance of dizygotic twinning. Specifically, the study found that vegan mothers (who exclude dairy from their diets) are one-fifth as likely to have twins as vegetarian or omnivore mothers, and concluded that "Genotypes favoring elevated IGF and diets including dairy products, especially in areas where growth hormone is given to cattle, appear to enhance the chances of multiple pregnancies due to ovarian stimulation. "From 1980 to 1997, the number of twin births in the United States rose 52%.