Risk factors associated with preterm birth according to gestational age at birth†

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To identify and quantify risk factors associated with preterm birth, stratified by gestational age at birth.


Three case-control analyses were done. Controls were pregnancies of ≥37 weeks of gestational age at birth. Cases were defined as: <28, 28–32, 33–<37 weeks of gestational age at birth respectively in the three case-control analyses. Women were categorized according to whether they carried single or multiple infants.


Obstetrical conditions (placenta previa, placental abruption), and maternal hypertension were significantly associated with preterm delivery in all case-control analyses (adjusted OR between 1.34–19.56, p < 0.05). Leading risk factors for preterm delivery in singleton pregnancies were placental abruption and placenta previa (adjusted ORs 4.85 and 4.13, p < 0.05). For multiple pregnancies they were polyhydramnios and maternal hypertension (adjusted ORs 4.39 and 2.45, p < 0.05).


Obstetrical conditions during the pregnancy and maternal hypertension are important risk factors for preterm birth. Copyright © 2008 John Wiley & Sons, Ltd.

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