Causes of Miscarriage
A miscarriage is the spontaneous loss of a pregnancy during the first 23 weeks. The physical signs of a miscarriage are usually cramping and bleeding. Whilst it might provide little comfort to those experiencing a pregnancy loss, the reality is that miscarriages often happen for no obvious reason and can rarely be prevented.
How common are miscarriages?
The topic of miscarriages remains fairly taboo, with many women reluctant or unable to talk about their experience. However, they are common, affecting approximately one in eight known pregnancies, with many more likely to have occurred before a woman knows that she is pregnant. Approximately 1% of women will experience recurrent miscarriages, meaning they have three or more in a row.
The risk of miscarriage reduces as a pregnancy progresses. About 80% of miscarriages happen during the first trimester, with fewer than 1% occurring after week 20 of pregnancy. This is why many women wait until they have reached 12 weeks before telling others they are pregnant.
What causes miscarriage?
Approximately 50% of miscarriages that happen during the first trimester are due to a chromosomal problem with the developing foetus. Usually there will be the wrong number of chromosomes – too many, or too few – which means the foetus is unable to survive. The risk of chromosomal abnormalities is higher in older women, which is one of the reasons why older mothers are more likely to experience miscarriages than younger women. In women over 45, more than 50% of pregnancies end in miscarriage.
Lifestyle factors can also increase the risk of miscarriage, for example:
- Obesity (Body Mass Index > 25kg/m²).
- Drug taking
- Excessive caffeine consumption (try to limit consumption to below 200mg per day).
- Environmental toxins/workplace hazards, e.g. working with radiation.
You should check with your healthcare provider before taking any medication during pregnancy as not all medicines are appropriate to take at this time. Specific examples of drugs that are best avoided include, retinoids (anti-acne), methotrexate (relief of rheumatoid arthritis) and non-steroidal anti-inflammatories (pain relief).
Some women have long-term (chronic) health conditions, which increase their risk of miscarriage, particularly if the condition is not well managed. Examples include:
- Auto-immune diseases (lupus)
- Kidney disease
- Thyroid issues
- Polycystic Ovary Syndrome (PCOS).
The connection between infertility and PCOS is well established. However, emerging evidence suggests that even if conception is successful, women with the condition are 2.5 times more likely to miscarry than their healthy counterparts. It is not yet clear whether ovulation induction therapy, using clomiphene citrate for example, increases a female’s risk of miscarrying; the available data to date is low quality and conflicting. However, women in this category usually have an underlying medical condition that has prompted their use of ovulation induction and may, therefore, already be at higher risk of miscarriage.
Infections and severe food poisoning can both increase the risk of miscarriage. This is one reason why women are advised to consider their diet during pregnancy and avoid those food types that are associated with a higher risk of food poisoning, for example unpasteurised dairy, undercooked meats, raw eggs and raw shellfish. Pregnant women should also limit the amount of tuna and oily fish that they eat.
Causes of late miscarriage
Experiencing a miscarriage during the second trimester can be particularly difficult to cope with. By now, you will have made it through the period that is typically considered to be most high-risk (the first 12 weeks) and are likely to have started telling more people and forming plans.
Some of the risks for late miscarriages are the same and women are encouraged to continue to consume a healthy diet and avoid smoking, drinking alcohol and taking recreational drugs. It is also important to ensure that chronic health conditions are under control and any medication is approved as safe for use during pregnancy by your doctor.
Unfortunately, as with early miscarriages, a lot of late miscarriages are unavoidable. Sometimes the uterus is an abnormal shape, or has unusual growths, such as fibroids that increase the risk of miscarriage.
In some cases, a female will have a weakened/incompetent cervix, which widens and opens during pregnancy. The cervix should remain closed until just before delivery. This muscular weakness can be due to previous injury, or surgery to the cervix. One treatment option for this is to undergo a cervical cerclage.
What does not increase the risk of miscarriage?
Despite concerns to the contrary, the following are not likely to cause a miscarriage:
- The mother’s emotional state (although remaining happy and calm throughout your pregnancy is definitely recommended and you should seek professional help if you do start to feel overwhelmed, anxious or depressed).
- Experiencing a shock or fright.
- Sexual intercourse. For most couples, continuing to have an intimate relationship during pregnancy is perfectly safe, provided of course, both parties want to. If your pregnancy is high risk, or you have had significant bleeding, your doctor might advise you to abstain.
- Exercise. Although you should always check with a professional before commencing any physical activity.
- Spicy food.
Experiencing a miscarriage can put both a physical and emotional strain on the body. Whilst some women may take comfort in knowing there was nothing they could have done to avoid it; for others, the lack of control over the situation can be difficult. Not knowing whether your pregnancy loss was an unfortunate one-off, or something you will experience again with subsequent pregnancies makes the healing process challenging. Take time to recover and talk through your emotions with friends and family.
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- “Early Pregnancy Loss.” ACOG, www.acog.org/clinical/clinical-guidance/practice-bulletin/articles/2018/11/early-pregnancy-loss.
- Legro, Richard S., et al. “Clomiphene, Metformin, or Both for Infertility in the Polycystic Ovary Syndrome.” New England Journal of Medicine, vol. 356, no. 6, 8 Feb. 2007, pp. 551–566., doi:10.1056/nejmoa063971.
- “Miscarriage – Causes.” NHS Choices, NHS, www.nhs.uk/conditions/miscarriage/causes/.
- “Miscarriage: Risks, Symptoms, Causes & Treatments.” Cleveland Clinic, my.clevelandclinic.org/health/diseases/9688-miscarriage.
- “What Are the Causes of and Risks for Pregnancy Loss (Before 20 Weeks of Pregnancy)?” Eunice Kennedy Shriver National Institute of Child Health and Human Development, U.S. Department of Health and Human Services, www.nichd.nih.gov/health/topics/pregnancyloss/conditioninfo/causes.
- Yu, Hai-Feng, et al. “Association between Polycystic Ovary Syndrome and the Risk of Pregnancy Complications.” Medicine, vol. 95, no. 51, 23 Dec. 2016, doi:10.1097/md.0000000000004863.