The nine months of pregnancy is traditionally divided into three trimesters: distinct periods of roughly three months in which different phases of fetal development take place. The first trimester is a time of basic cell differentiation. It is said to truly end at the mother’s first perception of fetal movement (quickening) which usually occurs around the end of the third month. The second trimester is a period of rapid growth and maturation of body systems. A second-trimester fetus born prematurely may be viable, given the best hospital care possible. The third trimester marks the final stage of fetal growth, in which systems are completed, fat accumulates under the soon- to-be-born baby’s skin, and the fetus at last moves into position for birth. This trimester ends, of course, with the birth itself. The word "trimester" came into English in 1821 from the French "trimestre." It, in turn, evolved from the Latin "trimestris" — from "tri-," three + "mensis," month. Trimester is thus related in origin to menses and menstruation. (In the UK, trimester is always a period in pregnancy. In the US, trimester also refers to a three-month period into which the school year may be divided.)
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A period of 3 months; one-third of the length of a pregnancy. [L. trimestris, of three-month duration]

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tri·mes·ter (')trī-'mes-tər, 'trī-. n a period of three or about three months esp any of three periods of approximately three months each into which a human pregnancy is divided

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(in obstetrics) any one of the three successive three-month periods (the first, second, and third trimesters) into which a pregnancy may be divided.

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tri·mes·ter (tri-mesґtər) a period of three months.

Medical dictionary. 2011.

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Look at other dictionaries:

  • Trimester — (lat.: tri ‚drei‘ und mensis ‚Monat‘ bzw. trimestris ‚dreimonatig‘) steht für: einen Zeitabschnitt von drei Monaten, siehe Quartal die Aufteilung des Studienjahres in vier Abschnitte zu je drei Monaten, siehe Trimester (Studium) ein… …   Deutsch Wikipedia

  • Trimester — Tri*mes ter, n. [L. trimestris of three months; tri (see {Tri }) + mensis month: cf. F. trimestre.] A term or period of three months. [1913 Webster] …   The Collaborative International Dictionary of English

  • trimester — trimester. См. триместр. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • Trimester — (v. gr.), eine Zeit von drei Monaten …   Pierer's Universal-Lexikon

  • Triméster — (lat.), Zeit von drei Monaten …   Meyers Großes Konversations-Lexikon

  • Triméster — (lat.), Zeit von 3 Monaten …   Kleines Konversations-Lexikon

  • trimester — 1821, period of three months, from Fr. trimestre (early 17c.), from L. trimestris of three months, from tri three + mensis month (see MOON (Cf. moon) (n.)). Specific obstetrics sense is attested from 1916 …   Etymology dictionary

  • Trimester — [Aufbauwortschatz (Rating 1500 3200)] Auch: • Semester Bsp.: • Das Herbstsemester hat begonnen …   Deutsch Wörterbuch

  • trimester — ► NOUN 1) a period of three months, especially as a division of the duration of pregnancy. 2) N. Amer. each of the three terms in an academic year. DERIVATIVES trimestral adjective trimestrial adjective. ORIGIN Latin trimestris, from tri three +… …   English terms dictionary

  • trimester — [trī mes′tər, trī′mes΄tər] n. [Fr trimestre < L trimestris, of three months < tri , three + mensis, month: see MOON] 1. a period or term of three months; specif., any of the three three month periods of a human pregnancy 2. in some colleges …   English World dictionary

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