Select the Meaning of the Underlined Word in the Sentence

Select the meaning of the underlined word in the sentence.
Julie started feeling contractions this morning and two hours after she was already meeting her baby.

A) a period of economic decline or negative growth
B) a reversible reduction in size
C) a word with omitted letter replaced by an apostrophe
D) a strong shortening of the uterine muscles prior to or during childbirth