Tilted uterus - A uterus that's tipped backward instead of normally forward on the cervix.

Tocolytic agents - Drugs used during premature labor to relax the uterus and halt contractions. Long term use of these drugs is not recommended.

Transverse lie - A position in which the fetus is turned sideways in the uterus

Trimester - Any of the three 3-month periods into which pregnancy is divided.

Triple screen - A prenatal blood test performed between 16 and 18 weeks to check levels of three substances that help determine whether a fetus is at increased risk for chromosomal abnormalities or neural tube defects.

Tubal ligation - A method of sterilization, rarely reversible, in which the fallopian tubes are either cut and tied off or clamped.

Transition labor - The tough-going, final part of the first stage of labor, when the cervix dilates eight to ten centimeters and a woman may begin to feel the urge to push. At this point in labor, contractions come in quick succession.

Tay-Sachs disease - An inherited disease characterized by mental retardation, blindness, convulsions, decreased muscle tone, and, eventually, death; found most often in Ashkenazi Jews and French Canadians.

Telemetry - An external fetal monitor, which utilizes two belts around the woman's abdomen, but allows her to walk around while carrying a small transmitter in her pocket, which radios information to a central monitor at the nurses' station.

TENS - (transcutaneous electrical nerve stimulation) A device for relief of labor pain. Sticky pads are attached to a woman's back and electrical impulses are sent through her skin to stimulate nerve pathways to the uterus and cervix. This simulation jams other sensory inputs along those pathways, such as pain.

Teratogen - An agent, including certain medications, chemicals, and infections, that can cross the placenta when a woman is exposed to it during pregnancy, causing miscarriage or birth defects.

Terbutaline - A drug used to stop preterm labor.

Thalassemia - A group of inherited disorders of hemoglobin metabolism causing mild to severe anemia; usually found in people of Mediterranean, black, Chinese, or Asian descent.

Toxoplasmosis - An infection that can cause blindness, retardation, and neural tube defects in the fetus. Because cats, birds, and fish can carry the parasite which causes toxoplasmosis, pregnant women should avoid changing litterboxes and cleaning bird cages or fish tanks or gardening. It can also be found in raw and rare meat and garden soil.