What Causes Stillbirth?

Stillbirth refers to the death of a baby before or during delivery and after 24 weeks of pregnancy. If a baby dies before 24 weeks of completed pregnancy, the term “miscarriage” or fetal loss applies instead.

In the UK, more than 3,600 babies are stillborn every year and stillbirth is fifteen times more common than cot death. Most stillbirths occur prior to labor, while a very small number happen during labor and delivery.

A large number of stillbirths seem to occur in babies that seem otherwise healthy and the cause is often unknown. Many people assume that stillbirth occurs as the result of a genetic defect, but in fact, this is only the cause in around 10% of cases. Sometimes, the mother has a condition that interferes with the pregnancy and in other cases there are placental problems or difficulties with the umbilical cord. Some of the causes of stillbirth that have been established are described in more detail below.

Problems with the Placenta

In around 50% of cases, stillbirth is linked to problems with the placenta, the organ that connects the baby’s blood supply to the mother’s blood supply so that the baby is nourished throughout the pregnancy. Experts believe that some “unexplained” stillbirths are caused by a poorly functioning placenta. The baby’s growth may be held back due to the oxygen and blood supply being compromised, but this deterioration may happen gradually and not necessarily be detected during routine antenatal checks.

In around one third of cases, babies that are stillborn have not reached their growth potential. Restricted growth or growth that begins normally, but then reduces during pregnancy is a signal that the baby may be at risk of being stillborn. In this case, a mother may begin to notice that the baby moves less frequently. A research study called AFFIRM is currently being conducted to investigate whether encouraging women to be aware of their baby’s movements and report any changes could help to lower the number of stillbirths.

Birth Defects

In around one in ten cases of stillbirth, the baby has a birth defect that contributed to the death. In some cases, a baby has structural abnormalities that are not a result of chromosomal defects, but occur due to environmental or unknown factors.

Infection

Around 10% of stillbirths are caused by infection, usually by bacteria that has infected the womb. These infections may not be noticed by the mother or diagnosed until serious problems have developed. Examples of bacteria that can cause such infection include E.coli, group B streptococcus, klebsiella, Chlamydia, haemophilus influenza, enterococcus, and mycoplasma or ureaplasma. Some of these infections such a Chlamydia are sexually transmitted and can be prevented by using barrier contraception such as condoms.

Other Conditions

A small proportion of stillbirths are caused by problems with the mother’s health such as pre-eclampsia or gestational diabetes. Other problems that may be associated with stillbirth include the following:

• Hemorrhage before or during labor
• Pre-eclampisa, a condition that causes high blood pressure in the mother
• Placental abruption, where the placenta becomes separated from the womb prior to birth
• An umbilical cord problem – the cord may slip through the cervix and into the womb or become caught around the baby’s neck
• Gestational diabetes, a form of diabetes that develops during pregnancy
• Intrahepatic cholestasis of pregnancy, a liver disorder that occurs during pregnancy

Unfortunately, in around one third of cases, the cause of stillbirth cannot be determined, despite best efforts to establish one.

Risk Factors

There are a number of factors that can increase a woman’s risk of having a stillbirth and these include the following:

• Multiple pregnancies
• A previous pregnancy loss
• Baby failing to reach growth potential in the womb
• Being aged 35 years or older
• Smoking cigarettes, drinking alcohol or misusing drugs during pregnancy
• Being obese (BMI over 30)
• A pre-existing health condition such as high blood pressure, epilepsy or diabetes
• Malnutrition
• Inadequate prenatal care