Every expectant parent hopes that pregnancy goes smoothly and that their baby will arrive healthy and on or around their anticipated due date. Sometimes, things don’t go according to plan, and a baby is born prematurely, requiring extra care and support to survive. Prematurity is the birth of a baby before 37 weeks. A full-term pregnancy, for comparison, lasts around 40. A preterm birth puts a baby at a higher risk of various health problems.

Their bodies may not yet be mature enough to cope well outside the womb. They may have difficulty breathing, feeding, or fending off infections.

Premature babies require special care to different degrees, depending on how early they arrive. The category of premature they are is also determined by their birthday. The three categories of premature babies are:

Extremely preterm: babies born before 28 weeks of gestation.
Very premature: babies born between 28 and 32 weeks of gestation.
Moderate to late preterm: babies born between 32 and 37 weeks of gestation.

Why might my baby be born prematurely?

More often than not, a premature birth happens spontaneously, and your doctor will not know why. A premature birth can also be planned when it's safer for mom and/or the baby for things to happen sooner. This could be because mom or baby has a health condition, such as severe pre-eclampsia, and it’s no longer safe to continue the pregnancy.

There are some things that increase the risk of going into labour early, so some moms may be told that they have a higher risk of giving birth early. They include your pregnancy history (including previous preterm births and a short interval since your last pregnancy), the health of a current pregnancy, whether it's a multiple birth (multiples carry a higher risk), your medical history, and who you are (e.g., your age, lifestyle habits, BMI, and ethnicity).

Other maternal factors that increase your risk of going into labour early include health conditions like high blood pressure, preeclampsia, diabetes, infections in the womb, and kidney disease. Infections in the reproductive tract, such as bacterial vaginosis, urinary tract infections, and sexually transmitted infections, can also lead to preterm birth.

Other risk factors

Low levels of PAPP-A (a hormone that is made by the placenta in pregnancy) may mean that the placenta (the organ that helps the baby grow and develop) may not work as well. There may be an increased chance of premature birth or pre-eclampsia.

Placenta praevia

This happens when the placenta attaches low down in the uterus and may cover part of or all of the cervix. In most cases, the placenta moves upwards and out of the way as pregnancy continues, but sometimes it doesn’t. This condition is known as low-lying placenta if the placenta is less than 20 mm from the cervix or as placenta praevia if the placenta covers the cervix. If you have placenta previa, you are at a higher risk of giving birth early.

Too much amniotic fluid (polyhydramnios)

Polyhydramnios is where there is too much amniotic fluid around your baby in the womb. This slightly increases the risk of pregnancy complications, including premature birth.

Preterm premature rupture of the membranes (PPROM, or waters breaking early)

If your waters broke early in a previous pregnancy, then there is a small chance that this will happen again. PPROM can cause a late miscarriage or premature birth.

Uterine abnormalities (unusually shaped womb)

A uterine abnormality is a womb that formed in an unusual way before a mother was born. Depending on the shape of her womb, there may be a higher risk of premature birth. Most women are unaware that they may have an abnormally shaped womb when they get pregnant. It is usually discovered during investigations into infertility or miscarriage.

Bleeding after 24 weeks

Bleeding after the first trimester can be a sign that there is a problem with the placenta, such as a low-lying placenta or placental abruption, which can both cause premature birth.

Any bleeding in pregnancy should be investigated, even if you are not experiencing any other symptoms. If you are more than 12 weeks pregnant and have bleeding, go to your local A&E or contact the hospital maternity unit immediately so you can be checked, just in case.

A weak cervix

Sometimes the neck of the womb (cervix) shortens during pregnancy, which may indicate that you are at risk of preterm birth. Doctors do not always know why this happens, but it can happen if the cervix has been damaged. For example, from a tear in childbirth or treatment for an abnormal cervical screening, such as largo loop excision of the transformation zone (LLETZ) or a cone biopsy.

When this happens, the cervix is called weak or incompetent, which means it could open or shorten early. This could lead to premature labour. If scans show that there is a problem with your cervix, you may be offered a cervical stitch (also known as a cerclage or cervical suture) or hormone treatment (such as progesterone) to stop your baby from being born too soon.

Understanding the causes and risk factors associated with prematurity is crucial for prevention, early detection, and appropriate management. Your doctor and midwife will take various steps to reduce the risk of preterm birth, including regular antenatal care, education about healthy lifestyle choices, screening and treatment for infections, and closer monitoring if your pregnancy is deemed high-risk.

Preterm birth not only poses immediate health challenges for the baby but may also have long-term effects on their development that are discussed later in this university journey.

Understanding Prematurity: Definition, Causes & Risk Factors

Unii’s Premature Baby Journey explores the causes and risks for preterm birth.