Risk factors

There are some additional risk factors that are associated with recurrent miscarriage and second trimester miscarriage. These are described in the relevant sections.

Chromosomal abnormalities account for half of all pregnancy losses. In most cases, this is a chance event during the very first stages of cell division following conception. Having too many, or too few chromosomes, impacts normal foetal development and can sadly result in the loss of pregnancy.¹ This is beyond anyone’s control, so there is no way to predict if this will happen.

If you experience recurrent miscarriages, you and your partner may be offered genetic testing to determine if there are any genetic abnormalities that could be inherited. You will usually be offered genetic counselling with a specialist if any risks are identified.²

Increasing maternal age is a risk factor for miscarriage and recurrent miscarriage. In women and birthing people aged 25–29 the risk is approximately 10%, but this increases to 53% if you are 45 years or older.³

These statistics only relate to risk; they do not mean that you cannot have a positive pregnancy outcome if you choose to have children later in life. In fact, over recent years, the number of live births are attributed to women and birthing people aged 30–39 years are increasing globally.^4,5

There is evidence to show that having a Body Mass Index (BMI) of ≥25.0 (categorised as overweight and obese) or <18.5 (underweight) can significantly increase the risk of having a miscarriage and recurrent miscarriage, versus a BMI of 18.5-24.9 (normal weight).^6,7

It is not fully understood why this is, but it is likely to be due to several different physiological reasons that may impact hormone function, inflammation, and implantation.^6,7

If you are worried about your weight, speak with your healthcare provider. They will be able to support you and provide you with further information on how to stay healthy during pregnancy.

Studies show that smokers more likely to experience pregnancy losses than non-smokers.⁸ The nicotine found in cigarettes can pass into the placenta and reduce the amount of oxygen your baby needs to develop healthily. There are no safe levels of nicotine in pregnancy, so it is advised to avoid any nicotine-containing products, including e-cigarettes.⁹

If you are in the process of quitting smoking and trying for a baby, don’t worry. Studies have indicated that women and birthing people who quit smoking were not at any increased risk of miscarriage to those who had never smoked.⁸

Smoking can be a difficult habit to break. Support is available so always speak with your healthcare provider if you are concerned or need further advice.

Alcohol is associated with a higher risk of miscarriage. Some studies show there is a heightened risk for miscarriage even at low levels.¹⁰ Therefore, there is no safe amount or type of alcohol in pregnancy.

Fortunately, the non-alcoholic beverage industry has boomed in recent years,¹¹ so there are many alcohol-free alternatives that you can choose instead.

It is hard to fathom how to get through a day without your cup of coffee or tea, especially if you are experiencing pregnancy related tiredness!

One study suggested that an additional cup of coffee consumed per day during pregnancy was associated with 3% increased risk for miscarriage.¹² To remove any risk, it would be best to avoid caffeine completely. However, this is not always possible. Pregnant women and birthing people should limit their caffeine intake to no more than 200 mg per day.¹³

Infections may be associated with up to 15% of miscarriages within the first trimester, and in up to 66% of second trimester losses.¹⁴

In pregnancy, your body alters the way your immune system works to support the growth of your baby. Unfortunately, this can make you more vulnerable to infection and more severe infection. Not all viral or bacterial infections will affect your baby, but there are some that are associated with a risk for miscarriage.¹⁴

Mainly, these include:¹⁴

• Rubella
• Herpes simplex virus
• Toxoplasmosis
• Chickenpox
• HIV
• Syphilis
• Parvovirus B19
• Cytomegalovirus

These can all be managed and treated, but you can mitigate the risk of exposure by avoiding raw, undercooked meat and eggs and unpasteurized cheeses, keeping up to date with any vaccinations offered to you during your pregnancy, avoid handling cat litter, and maintaining good hygiene.

Speak with your healthcare provider if you are concerned or need additional advice and information.

There are some medications that may increase your risk for miscarriage.

These include:

• Misoprostol which is used for stomach ulcers¹⁵
• Oral retinoids, such as isotretinoin, which are used to treat skin conditions such as eczema and acne^16,17
• Methotrexate which is prescribed for conditions such as rheumatoid arthritis¹⁸
• Non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, which are used to relieve pain and inflammation¹⁹

If you are on any of these medications and are pregnant, or are planning to start a family, speak with your healthcare provider to discuss alternatives. Always speak with your healthcare provider to confirm if a medicine is considered safe to take in pregnancy before taking it.

Polyendocrine metabolic ovarian syndrome (PMOD) (previously polycystic ovary syndrome; PCOS)

Polyendocrine metabolic ovarian syndrome (PMOD) (previously polycystic ovary syndrome; PCOS) is the most common endocrine disorder in biological women of reproductive age.²⁰ In PCOS, hormonal changes disrupt normal ovarian function, often leading to enlarged ovaries and preventing regular ovulation.²¹

Women with PCOS are three times more likely to experience a pregnancy loss. It is unclear why this is, but it is likely due to number of different factors.²²

Although having PCOS can increase the risk, it does not mean that you will have a miscarriage. It is important to speak with your healthcare provider for further advice and information.