There are many causes and risk factors for a miscarriage. In most cases, however, a pregnancy loss cannot be avoided.
Key Facts:
- Most miscarriages occur within the first 12 weeks
- The most common cause of a miscarriage in the first trimester is a chromosomal disorder
- Between 12 and 20 weeks, miscarriages become less common and are often due to cervical weakness
- Two or more miscarriages are referred to as recurrent miscarriages
- Most women can have healthy pregnancies following a miscarriage
Introduction
In many instances, the specific cause of a miscarriage remains unknown. However, in most cases, it stems from genetic abnormalities in the embryo that stop further development. The reasons for a miscarriage can vary based on the stage of pregnancy.
This article explores the most common causes and risk factors associated with miscarriage.
What is a miscarriage?
A miscarriage, or spontaneous abortion, is defined as the loss of a pregnancy before the 20th week (counted from the first day of the last menstruation). An early miscarriage occurs in the first trimester and is the most common type.
A late miscarriage happens between the 14th and 20th week of pregnancy and is less common. If the foetus dies in the womb after the 20th week of pregnancy and/or has a birth weight of 500 grams, it is referred to as a stillbirth.
What are the possible causes of a miscarriage?
- Genetic abnormality of the foetus or embryo: The most common cause of miscarriage is a chromosomal abnormality of the foetus or embryo that prevents normal development. This accounts for 40-50% of miscarriages in the first trimester. As the cause is genetic, it is not preventable. In most cases, it is a spontaneous disorder during foetal development for which neither parent is responsible.
- Certain health problems of the expectant mother: These can include hormonal disorders, blood clotting disorders, fibroids, polyps, a malformation of the uterus, or cervical insufficiency (cervical insufficiency). Other possible causes are diabetes mellitus, thyroid disease, certain immune diseases such as lupus or coeliac disease.
- Infections: Infections like toxoplasmosis, rubella, listeriosis, salmonella, or cytomegalovirus can also trigger a miscarriage.
- Detachment of the placenta: Placental abruption can be caused by a severe fall, a car accident, or violence. If the placenta detaches prematurely, the unborn child can no longer be cared for.
- Age of the mother: The risk of miscarriage increases with the mother's age. More than half (53%) of all pregnancies at the age of 45 end in miscarriage, compared to only 10% of 20-year-old pregnant women.
- High blood pressure: While not a direct cause, high blood pressure can constrict the blood vessels and impair blood flow to the placenta. This might lead to a miscarriage due to the unborn child not receiving enough oxygen and nutrients.
- Smoking: Smoking during pregnancy increases the risk of miscarriage by 24-32%. Passive smoking also increases the risk by 11%.
- Alcohol: According to a large-scale Danish study, women who consumed five or more alcoholic drinks per week in the first trimester have a 5-fold increased risk of spontaneous abortion in the first trimester.
- Amniocentesis: Approximately 1% of amniocenteses can lead to a miscarriage.
Can stress cause a miscarriage?
The scientific community has not definitively proven whether stress can cause a miscarriage. However, a meta-analysis found that women who were stressed before or during the early stages of pregnancy had a 42% increased risk of miscarriage.
To learn more about the impact of stress, consider reading our article "How Does Stress Affect Fertility?".
What are the risk factors for miscarriage?
Chronic illnesses and abnormalities of the uterus can increase the risk of miscarriage. Other risk factors include:
Parental age:
- Maternal age: The risk of miscarriage increases with the mother's age. It's around 10% for women under 30, and can rise to over 50% for women over 45.
- Paternal age: The father's age also plays a role. Men over 40 are more likely to have sperm with chromosomal abnormalities, potentially increasing the risk of miscarriage.
Repeated miscarriages:
- One miscarriage: A single miscarriage usually doesn't affect the success of future pregnancies.
- Two or more miscarriages: Two consecutive miscarriages with the same partner increase the risk of another miscarriage. Three or more miscarriages are considered recurrent miscarriages (recurrent pregnancy loss), warranting a thorough investigation into the causes.
When do miscarriages most frequently occur?
Most miscarriages occur in the first 12 weeks of pregnancy, making up 80% of cases. However, studies indicate that the risk of miscarriage drops to approximately 3% in the 8th week if an embryo heartbeat is detected.
Between the 12th and 20th weeks, it's relatively rare to lose a pregnancy. This usually arises from an issue with the cervix.
When can I get pregnant again after a miscarriage?
Women can often conceive again quickly after an early and uncomplicated miscarriage. However, it's recommended to wait until the first normal menstrual cycle to allow the hormone balance to stabilise. This process varies among women.
Even if a curettage was performed, there is usually no specific waiting period for a new pregnancy. If you plan to become pregnant again soon, continue taking folic acid. However, if your pregnancy was further along, it may be advisable to wait a few months for your body to recover.
What are the signs of a miscarriage?
Miscarriage signs include:
- Vaginal bleeding
- Abdominal pain
- Sudden disappearance of some pregnancy symptoms, e.g., no more breast pain or nausea and vomiting
- Contractions or labour pains similar to childbirth
A gynaecologist can also check the pregnancy hormone hCG (human chorionic gonadotropin) levels through a blood sample. This hormone should double every 2 to 3 days in the early stages.
What happens during a miscarriage?
Every miscarriage is unique and unfolds differently. If you experience light or heavy bleeding and pain during pregnancy, contact your gynaecologist immediately.
Most women who've had a miscarriage can have healthy pregnancies later. There are different types of miscarriages, each differing in symptoms and outcomes:
- Missed Abortion: The embryo dies, but the body does not expel it. There's no bleeding or pain, but pregnancy symptoms may decrease. A missed abortion is usually detected during an ultrasound scan.
- Threatened miscarriage: Characterised by slight bleeding and/or abdominal pain. The cervix is closed and it may still be possible to sustain the pregnancy.
- Incomplete abortion: The embryo or tissue remnants such as the endometrial lining are partially expelled, causing heavy bleeding and cramps. Curettage may be necessary to remove any remaining tissue.
- Complete abortion: The embryo and pregnancy tissue are completely expelled. Curettage is generally not required.
- Septic abortion: An infection of the uterus causes fever and pain. Immediate treatment with antibiotics and, if necessary, curettage is required.
How do I deal with a miscarriage?
A miscarriage can be a devastating event. It's crucial that women or couples give themselves ample time to recover before trying again. Seeking professional help from a psychotherapist can also aid in processing the experience.
Conclusion
Miscarriages often happen unexpectedly and can be caused by various factors. The likelihood of a miscarriage is highest in the first trimester, usually due to chromosomal abnormalities in the embryo. Later on, a weak cervix can result in premature birth or miscarriage.
In most instances, a miscarriage cannot be prevented. However, certain factors such as the parents' age can increase the risk. For instance, more than half of pregnancies in women over 45 result in miscarriage.
If you've experienced one or more miscarriages, a detailed fertility check can help determine possible causes. Additional tests such as coagulation diagnostics or immunological tests may also be conducted.
Interested in learning more? Book your appointment for a free initial consultation.
