In a small number of cases, signs of TS do not become apparent until a girl reaches her teens or even early adulthood.  A female that is consistently well below average height or seems to never experience a "growth spurt" may benefit from testing for TS. Generally speaking, if a teen girl is 8 inches (20 cm) or more below average height, testing for TS may be warranted. Most females with TS have ovarian failure that causes infertility and prevents the onset of puberty.  This failure can occur early in life or progressively over time, making it possible that it will not become apparent until the teen years. If there is little indication of the start of puberty — body hair growth, breast development, menstruation, sexual maturation, etc. — in a girl who is well into her teens, TS should be considered a strong possibility. TS can also impact the mental and emotional development of some females, and these effects may not be as noticeable during early childhood.  If, however, as a teen or young adult, a girl has social difficulties due to an inability to "read" others' emotions and responses, TS should be considered. Additionally, teen girls with TS may have a particular learning disability in regards to spatial concepts.  This, for instance, may become more apparent as mathematics classes become increasingly advanced.  This doesn't mean that any girl having trouble in math class has TS, of course, but it may be worth consideration when other factors are present. Just because a girl is especially short, has kidney problems, has a low hairline on the neck, or has not started puberty by the typical age range does not mean she has TS.  Visual cues and common symptoms can only indicate TS; a medical diagnosis via genetic testing is the only way to confirm the condition.  Karyotype genetic testing to accurately diagnose TS requires only a blood draw and a wait of a week or two for the lab results.  It is simple and highly accurate. Most cases of TS are detected and diagnosed before or shortly after birth, but if you suspect an undiagnosed case, seek a medical opinion promptly.  The sooner the condition is confirmed (if present), the sooner important treatments can begin.  A timely use of growth hormones, for instance, can make a significant difference in the final height of a female with TS.

Summary:
Watch for a growth rate that is well below average. Take notice if signs of puberty's onset are missing. Look for specific learning and social difficulties. See a doctor to confirm your suspicions.