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Preterm birth (PTB), also known as premature birth, is the birth of a baby at fewer than 37 weeks' gestational age, as opposed to full-term delivery at approximately 40 weeks. PTB is defined as birth before 37 weeks' gestation, very early PTB is before 32 weeks, early PTB occurs around 32–36 weeks, late PTB is between 34–36 weeks' gestation and early-term birth is delivered at 37–38 weeks' gestation Late PTB accounts for 75% of all PTB.

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