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testicle (testis) — the male sex gland. There are a pair of testes behind the penis in a pouch of skin called the scrotum. The testes make and store sperm, and make the male hormone testosterone.

thalassemia — a group of blood diseases, that are inherited, which affect a person's hemoglobin and cause anemia. Hemoglobin is a protein in red blood cells that carries oxygen and nutrients to cells in the body.

thrush — a yeast infection, caused by the fungus Candida albicans, of the mouth and throat. It's hallmark is white patches in the mouth. It can also occur in the gastrointestinal tract and vagina, and causes some types of diaper rash in infants.

thyroid — The thyroid is a small gland in the neck that makes and stores hormones that help regulate heart rate, blood pressure, body temperature, and the rate at which food is converted into energy.

tonsillitis — inflammation of the tonsils, which are lymph nodes in the back of the mouth at the top of the throat. Tonsils help to filter out bacteria and other microorganisms to prevent infection in the body. When they become overwhelmed by bacterial or viral infection they can become swollen and inflamed.

toxemia — see preeclampsia.

toxoplasmosis — an infection caused by the parasite named Toxoplasma gondii that can invade tissues and damage the brain, especially in a fetus and in a newborn baby. Symptoms include fever, fatigue, headache, swollen lymph glands, and muscle aches and pains. Can be contracted by touching the hands to the mouth after gardening, cleaning a cat's litter box, or anything that came into contact with cat feces; or by eating raw or partly cooked meat, or touching the hands to the mouth after touching raw or undercooked meat.

transient ischemic attack (TIA) — a "mini-stroke" where there is a short-term reduction in blood flow to the brain usually resulting in temporary stoke symptoms. Does not cause damage to the brain, but puts a person at higher risk of having a full stroke.

trichomoniasis — a very common STD in both women and men that is caused by a parasite that is passed from one person to another during sexual contact. It also can be passed through contact with damp, moist objects such as towels or wet clothing. Symptoms include yellow, green, or gray vaginal discharge (often foamy) with a strong odor; discomfort during sex and when urinating; irritation and itching of the genital area; or lower abdominal pain (rare).

trimester — A typical pregnancy is 9 months long. Pregnancy is divided into three time periods, or trimesters, that are each about three months in duration - the first, second, and third trimesters.

triple screen — blood test that indicates if there’s an increased risk of a birth defect, or a condition like Down Syndrome, in the fetus. This test can also show twins.