10 Things that Increase the Risk of Miscarriage

Miscarriages are common, with 1 in 5 of all known pregnancies ending in miscarriage. Most of the time, miscarriage is due to chromosomal abnormalities in the embryo, and there is very little that can be done. That said, while any woman can miscarry, there are some who are more likely to miscarry than others.

Here are 10 of the most common risk factors:

#1 – Age

All women are born with a finite number of eggs – between 1 million and 2 million. While this may seem like a large number, the vast majority of eggs within the ovaries steadily die. By the time a woman reaches puberty, only 300,000 or so eggs remain, and of these, only 500 will be ovulated during a woman’s reproductive lifetime. Menopause occurs when a woman runs out of eggs.

What this means is that as a woman gets older, not only does she have fewer eggs, the eggs she has are less robust in terms of their genetic material. Women who are 40 years old are twice as likely to release eggs with chromosomal abnormalities and miscarry, than women who are 20 years old.

#2 – Uterine or Cervical Problems

Uterine abnormalities that can increase the risk of miscarriage include:

  • Congenital uterine abnormalities, such as a bicornuate uterus
  • A weak or unusually short cervix
  • Severe uterine scarring, which can be caused by problems during earlier labours

#3 – Chronic Diseases

There are a number of chronic diseases that can increase the risk of miscarriage. The most common are poorly controlled diabetes, and Polycystic Ovarian Syndrome (PCOS). Insulin-resistant PCOS can inhibit the production of progesterone, which is required throughout pregnancy but particularly in the early stages to build up the lining of the uterus and support any implanted eggs. If not enough progesterone is produced, the lining of the uterus can break down causing a miscarriage.

Less common chronic disorders that increase the risk of miscarriage include autoimmune disorders such as Antiphospholipid Syndrome (APS) and lupus, and certain inherited blood clotting disorders.

#4 – Infections

There are a number of common infections that have been shown to slightly increase the risk of miscarriage. These include mumps, rubella, measles, cytomegalovirus, parvovirus, gonorrhoea, and HIV.

A more serious infection is Listeriosis, involving the bacteria Listeria. Listeria is an illness caused by eating foods contaminated by the bacteria Listeria Monocytogenes. Listeria is most commonly found in unpasteurised soft cheeses, reheated food and seafood. Listeria infection, also known as listeriosis, is not dangerous for most adults, but for babies in the womb it can prove fatal. Even mild listeriosis can cause miscarriage, still birth, premature birth, or a baby who is very ill when born.

#5 – Substance Abuse

Smoking, drinking alcohol and using drugs such as cocaine and ecstasy have all been shown to increase the risk of miscarriage. Smoking alone increases the risk of miscarriage by 1% for each cigarette smoked daily. So if you smoked 40 cigarettes per day, your risk of miscarriage would increase by 40%. A recent study found that second hand exposure to cigarette smoke also increased the risk of miscarriage by 11%.

Due to conflicting conclusions from numerous studies regarding the impact of caffeine on pregnancy – one study showed women who consume more than 200mg of caffeine per day were twice as likely to miscarry as those who did not consume any caffeine; a second study showed that women who consumed between 200mg and 350mg of caffeine per day had no increased risk of miscarriage – women are advised to consume no more than 200mg of caffeine per day, equivalent to one 12oz cup of coffee.

#6 – Medications

Several medications, including over-the-counter drugs and prescriptions, have been linked to an increased risk of miscarriage, including non-steroidal anti-inflammatories such as aspirin and ibuprofen. Others include:

#7 – Environmental Toxins

Exposure to radiation or anaesthetics, along with substances like lead, arsenic, and a selection of common chemicals (formaldehyde, benzene and ethylene oxide) can all increase the risk of miscarriage. Recent studies have shown that the presence of plastics, pesticides and air pollutants, along with endocrine-disrupting chemicals, are causing a steady rise in the number of miscarriages and stillbirths globally.

#8 – Obesity

Obesity is associated with an increased risk of first trimester and recurrent miscarriage. Having an obese BMI (over 30) also increases the risk of gestational diabetes, heart problems, and difficulties delivering the baby naturally.

#9 – Paternal Factors

Although little is known about the impact of a father’s physical condition on the likelihood of miscarriage, it has been found that there is a greater risk of miscarriage if the father is exposed to mercury, lead, some industrial chemicals and pesticides.

A molar pregnancy is what happens when both sets of chromosomes are provided by the father, instead of one being provided by the father and one by the mother. When this happens, the foetus usually does not develop at all. A partial molar pregnancy is when the mother provides one set of chromosomes and the father provides two. Again, it is impossible for a healthy baby to develop in these circumstances.

Luckily, molar pregnancies are rare, affecting one in every 1,000 pregnancies.

#10 – A History of Miscarriages, Birth Defects or Genetic Problems

Women who have miscarried two or more times in a row are more likely to miscarry than women who have not miscarried at all, or only miscarried once. Three or more miscarriages in a row are known as recurrent miscarriage. Genetic abnormalities – whether identified in a couple, in the wider family, in a previous pregnancy or in the birth defects of an older child – have all been shown to increase the risk of miscarriage.

Finally, it’s worth noting that invasive pregnancy tests such as chorionic villus sampling and amniocentesis do also increase the risk of miscarriage. Fortunately, the widespread availability of non-invasive pregnancy tests (NIPTs) means that this is a risk that no longer needs to be taken.


  • https://www.babycenter.com/0_miscarriage-signs-causes-and-treatment_252.bc
  • https://www.webmd.com/menopause/qa/how-many-eggs-does-a-woman-have
  • Maternal caffeine consumption during pregnancy and the risk of miscarriage: A prospective cohort study. American Journal of Obstetrics and Gynecology, 198, e1-8.. Weng, X., Odouli, R. & Li, D.K. (2008)
  • https://www.betterhealth.vic.gov.au/health/healthyliving/food-poisoning-listeria
  • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3969532/
  • https://www.health24.com/Parenting/Fertility/About-fertility/How-toxic-chemicals-are-causing-miscarriages-stillbirths-and-other-health-problems-20151006-2
  • https://www.ncbi.nlm.nih.gov/pubmed/15142995
  • https://www.mayoclinic.org/diseases-conditions/pregnancy-loss-miscarriage/symptoms-causes/syc-20354298
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