ballottement

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A palpatory technique for detecting or examining a floating object in the body, as.
• noun The use of a finger to push sharply against the uterus and detect the presence or position of a fetus by its return impact.
• noun Palpation of the abdominal wall while a kidney is being pushed sharply from the backside, used as a test for determining the presence of a floating kidney.

from The Century Dictionary.

• noun It consists of palpation, to determine the presence of a movable body in the abdomen, such as a child in the womb, a floating kidney, etc., by a sudden tap with the finger from below; this forces the body upward, and it can be felt again as it settles down upon the tip of the finger. Also called repercussion.
• noun In obstetrics, a method of testing pregnancy.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun medicine A method of diagnosing pregnancy, in which the uterus is pushed with a finger to feel whether a foetus moves away and returns again.
• noun medicine An increased amount of fluid in the suprapatellar pouch of the knee.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a palpatory technique for feeling a floating object in the body (especially for determining the position of a fetus by feeling the rebound of the fetus after a quick digital tap on the wall of the uterus)