Causes of preterm birth

Causes of preterm birth

A baby may be born prematurely as a result of preterm labour or because an earlier birth is recommended, due to complications that may have arisen during the pregnancy (affecting the mother or the baby). In many cases, it is not clear why labour starts early, however factors known to increase the risk of preterm labour include the following;
  • premature rupture of the membranes (your waters breaking early)
  • some infections, such as chorioamnionitis, which effects the membranes and amniotic fluid protecting the baby
  • multiple pregnancy (the average twin pregnancy is 37 weeks in length, and the average triplet pregnancy is 33 weeks in length)
  • previous preterm delivery
  • having a placenta that is ‘low-lying’ (meaning it either partially or completely covers the cervix) or having a placental abruption (meaning the placenta starts to separate from the wall of the womb)
  • maternal medical conditions, including diabetes or conditions linked to inflammation (eg. Crohn’s disease)
  • being a smoker, drinking alcohol or using illegal substances
  • low Body Mass Index (having a weight that is considered to be low for your height)
  • biopsies or LLETZ treatments to remove abnormal cervical cells
  • having a weak cervix that might open during pregnancy
  • polyhydramnios (excessive amniotic fluid)
  • intrahepatic cholestasis of pregnancy (a pregnancy condition affecting your liver)
  • abnormalities of the shape of the womb
Sometimes, you may develop a complication during your pregnancy and your healthcare professional may recommend preterm delivery. Examples of conditions that may require preterm delivery include:
  • moderate to severe pre-eclampsia (a pregnancy condition causing high blood pressure which can also affect some of your internal organs)
  • poorly controlled diabetes
  • intrauterine growth restriction (when your baby’s growth slows down or stops)
  • if your waters break early and you are developing an infection
  • other medical complications of pregnancy.
Women who are considered to be at risk of starting labour prematurely may be offered treatment to maintain the pregnancy for as long as is safely possible.

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