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A large proportion of stillbirths happen in otherwise healthy babies, and the reason often can't be explained. But there are some causes we do know about.

Many stillbirths are linked to complications with the placenta. The placenta is the organ that links the baby's blood supply to the mother's and nourishes the baby in the womb.

If there have been problems with the placenta, stillborn babies are usually born perfectly formed, although often small.

With more research, it's hoped that placental causes may be better understood, leading to improved detection and better care for these babies.

Other conditions that can cause or may be associated with stillbirth include:

• bleeding (haemorrhage) before or during labour
• placental abruption – where the placenta separates from the womb before the baby is born (there may be bleeding or abdominal pain)
• pre-eclampsia – a condition that causes high blood pressure in the mother
• a problem with the umbilical cord, which attaches the placenta to the baby's tummy button – the cord can slip down through the entrance of the womb before the baby is born (cord prolapse) or can be wrapped around the baby and become knotted 
• intrahepatic cholestasis of pregnancy (ICP) or obstetric cholestasis – a liver disorder associated with severe itching during pregnancy
• a genetic physical defect in the baby
• pre-existing diabetes
• an infection in the mother that also affects the baby

Usually this will be a bacterial infection that travels from the vagina into the womb (uterus). These bacteria include group B streptococcus, E. coli, klebsiella, enterococcus, Haemophilus influenza, chlamydia, and mycoplasma or ureaplasma.

Some bacterial infections, such as chlamydia and mycoplasma or ureaplasma, which are sexually transmitted infections, can be prevented by using condoms during sex.

Other infections that can cause stillbirths include:  

• rubella – commonly known as German measles
• flu – it's recommended that all pregnant women have the seasonal flu vaccine, regardless of stage of pregnancy
• parvovirus B19 – this causes slapped cheek syndrome, a common childhood infection that's dangerous for pregnant women
• coxsackie virus – this can cause hand, foot and mouth disease in humans
• cytomegalovirus – a common virus spread through bodily fluids, such as saliva or urine, which often causes few symptoms in the mother
• herpes simplex – the virus that causes genital herpes and cold sores
• listeriosis – an infection that usually develops after eating food contaminated by listeria bacteria (see foods to avoid in pregnancy)
• leptospirosis – a bacterial infection spread by animals such as mice and rats
• Lyme disease – a bacterial infection spread by infected ticks
• Q fever – a bacterial infection caught from animals such as sheep, goats and cows
• toxoplasmosis – an infection caused by a parasite found in soil and cat faeces
• malaria – a serious tropical disease spread by mosquitoes

There are also a number of things that may increase your risk of having a stillborn baby, including:

• having twins or a multiple pregnancy
• having a baby who doesn't grow as they should in the womb
• being over 35 years of age
• smoking, drinking alcohol or misusing drugs while pregnant
• being obese – having a body mass index above 30
• having a pre-existing physical health condition, such as epilepsy

Your midwife will check the growth and wellbeing of your baby at each antenatal appointment and plot the baby's growth on a chart.

Every baby is different and should grow to the size that's normal for them. Some babies are naturally small, but all babies should continue to grow steadily throughout pregnancy.

If a baby is smaller than expected or their growth pattern tails off as the pregnancy continues, it may be because the placenta isn't working properly. This increases the risk of stillbirth.

Problems with a baby's growth should be picked up during antenatal appointments.

It's important to be aware of your baby's movements and know what's normal for your baby.

Tell your midwife immediately if you notice the baby's movements slowing down or stopping. Don't wait until the next day.

See preventing stillbirth for more information.