What is a miscarriage?

A miscarriage is the unintentional loss of a growing baby before it can survive on its own. Miscarriages are more common than one would expect. More than a third of all pregnancies end in a miscarriage – often at a very early stage and unnoticed. A somewhat delayed, unusually severe menstrual period could be an indication of an early miscarriage.

An early miscarriage is one that occurs at any time up to the 13th week of pregnancy. After that point, the miscarriage would be considered a late miscarriage. More than 90 percent of all miscarriages are early miscarriages. The development of the embryo often stops before a heartbeat can be detected by an ultrasound. If your doctor detects the pregnancy hormone in your blood without an embryo being visible in the uterus, it is called a biochemical pregnancy.

The more advanced the pregnancy, the lower the risk of miscarriage. Studies show that once an ultrasound can detect a fetal heartbeat, the risk of miscarriage drops to less than 15 percent. Another important hurdle is the 13th week of pregnancy. From the 15th week of pregnancy onwards, the risk of miscarriage is lower than 3 percent depending on your age.

Causes of miscarriage and how to prevent it

If you have suffered a miscarriage, you’ll naturally ask yourself many questions. One of them is “Why?” Unfortunately, medicine is somewhat in the dark about the reasons that lead to a miscarriage, which is because it is rarely possible to examine the deceased embryo, especially in very early miscarriages.

Some studies on the subject have found that damage to or malformation of the baby’s DNA (i.e., chromosome abnormalities) is the most common cause for miscarriages. Other studies suggest that the female immune system is responsible for about half of all miscarriages because it accidentally identifies the embryo as “foreign” and rejects it. These results should be interpreted according to the age of the woman because genetic abnormalities are less likely to play a role in pregnancy loss in women under 32 than in older women.

Chromosome abnormalities

The most common chromosome abnormalities are trisomy 21 (Down syndrome) and sex chromosome abnormalities. In trisomy 21, the 21st chromosome is present three times instead of twice. In many cases, the abnormality leads to miscarriage. However, children born with trisomy 21 are usually viable.

Down Syndrome Trisomy 21 miscarriage

Fig.: Down syndrome.

The second most frequently diagnosed chromosomal peculiarities include deviations of the X and Y chromosomes (sex chromosomes) – in particular, Turner syndrome and Klinefelter syndrome. On the one hand, most of the pregnancies with a sex chromosome abnormality end in a miscarriage ; on the other hand, almost all children born with a sex chromosome anomaly are comparatively unaffected.

Girls or women with Turner syndrome have only one X chromosome (XO) instead of two  (XX). While this situation does not result in intellectual impairment, women with Turner syndrome have malformations of the genital organs and are, therefore, infertile.

Turner Syndrome Chromosomes miscarriage Fehlgeburt

Fig.: Turner syndrome.

Boys and men with Klinefelter syndrome have two X chromosomes (XXY instead of XY) in addition to the Y chromosome. Here, too, the chromosomal anomaly is characterized by infertility (e.g., immobility of sperm).

Klinefelter Syndrome Chromosomes

Fig.: Klinefelter syndrome.

The risk of chromosomal abnormalities increases with your age, with a significant increase in risk at the age of 31 and then again at the age of 37. In women over 40, more than half of all eggs have genetic defects. One prevention method is, therefore, to have children before your mid-30s. Of course, it is often easier said than done and not feasible or desired by many women.

Another prevention method is to increase folic acid intake several months before the planned pregnancy. Folic acid promotes the correct cell division and development of primary and secondary follicles, counteracting DNA damage.

Folic acid promotes the correct cell division and development of primary and secondary follicles counteracting DNA damage.

Women who have had multiple miscarriages can have their embryos genetically examined as part of in vitro fertilization (IVF). Only those embryos (where possible) that do not have a chromosomal defect are then transferred back into the uterus.

Immune system

Numerous overreactions in the immune system can lead to miscarriage. Ultimately, due to the paternal DNA, the embryo is half foreign to the female organism, which poses a particular challenge to the immune system.

There doesn’t have to be an actual autoimmune disease present for the female immune system to cause a miscarriage. Even moderately elevated levels of certain antibodies – for example, the antibodies against nuclear antigens (ANA) or against cytoplasmic antigens (ANCA) – are sufficient cause for the body to turn against a fertilized egg.

Among the many possible immunological causes of miscarriage are:

  • Hyperthyroidism
  • Hypothyroidism
  • Hashimoto’s thyroiditis
  • Increased thyroid antibodies
  • Female antibodies against the sperm of the male partner
  • Dysbalance of the T-helper cells (Th1/Th2 imbalance)
  • Natural killer cells in the uterus
  • Antiphospholipid antibodies (lupus antibodies)
  • Autoimmune diseases such as multiple sclerosis or rheumatoid arthritis

In a broader sense, blood clotting disorders are also an overreaction of the immune system. However, they get a separate chapter here because of their diversity.

A good way to prevent the immune system from becoming overly effective is to balance the intestinal mucosal immune system. Hundreds of bacterial strains regulate the intestinal immune response, and by adding certain probiotics and prebiotics to your diet, you can positively influence your immune system’s balance.

If you have already suffered more than one miscarriage, I recommend a comprehensive immunological assessment. The result of your blood work will be many pages long because there are many different antibodies and immunoglobulins in your blood. Treatment of an overactive immune system includes cortisone, aspirin, heparins, immunoglobulins, thyroid hormones, and many other options.

Treating of an overactive immune system is a lot cheaper than IVF. At the same time, IVF doesn’t solve the problem of an overactive immune system. 

If you have suffered a miscarriage and suspect your immune system may be involved, just reach out to me at silvia@fertinesse.com. I am happy to help! 

Blood clotting disorders

Abnormal clotting of your blood poses a threat to the the development of your embryo. The vessels that supply the embryo with blood during the first few weeks of pregnancy are extremely thin. Thick blood can keep the embryo from implanting properly or can lead to a limited blood supply, causing the embryo to die. At a later stage of pregnancy, increased blood clotting may prevent the placenta from functioning normally, resulting in a late miscarriage.

One of the most commonly associated blood clotting disorders associated with miscarriage is an autoimmune disease called anti-phospholipid syndrome. About 15 percent of women who suffer repeated miscarriages carry antiphospholipid antibodies.

Other blood clotting disorders that may cause miscarriage include:

  • Factor V mutation (APC resistance)
  • Protein C deficiency
  • Protein S deficiency
  • Antithrombin deficiency
  • Increased factor VIII levels
  • Prothrombin mutation
  • Hyperhomocysteinemia

Important: Regardless of the increased risk of miscarriage, women with a blood clotting disorder have an increased risk of deep vein thrombosis, a possibly life-threatening condition, especially during pregnancy. Any blood clotting disorder should, therefore, be treated.

Smoking and severe obesity also lead to an increase in blood clotting. Smokers and women with severely elevated BMIs are more than twice as likely to suffer a miscarriage.


Fig.: Blood clotting disorders can cause miscarriage and deep vein thrombosis


Late miscarriages are usually due to infections. Unfortunately, they are possible until the date of birth, although it is very rare. Infections are typically caused by bacteria (chlamydia, B-streptococcus, listeria), viruses (rubella, measles, herpes), and parasites (toxoplasmosis).

To prevent infections, you can do quite a bit:

  • Keep your vaginal pH at 3.8 to 4.5 by avoiding soap and douching.
  • Have a vaginal smear done before getting pregnant.
  • Make sure your vaccinations are up to date.
  • Avoid food that may contain toxoplasma (if you have tested toxoplasmosis-negative) or listeria, such as raw beef, sushi, and fresh cheese.
  • Pay attention to special hygiene during sexual intercourse.

As part of my fertility coaching, I am happy to show you how to measure your pH and advise you on which food to avoid. Just contact me at silvia@fertinesse.com!

Uterus Malformations

One of the most common malformations of the uterus is a central membrane (septum). The septum can vary in length and thickness. If the septum divides the uterus into two halves, it is called “uterus bicornis”. In contrast to the rest of the uterine lining, the septum is poorly supplied with blood. 

If a fertilized egg implants at the lining of the septum, the embryo will not be adequately supplied with blood and will eventually die. The poor blood supply is also the reason why this malformation is difficult to detect by ultrasound. Whether surgical treatment is necessary to remove the septum will be decided by your gynecologist. Usually, the septum can be removed through the vagina without problems. In most cases, women who lose a baby due to a septum are more fortunate in the following pregnancy, and the embryo chooses a better place for implantation.

Unfortunately, you can’t do too much to prevent it. My tip: after a miscarriage, insist on a detailed examination with a high-resolution ultrasound device.

uterus malformations miscarriage

Fig.: From left to right: normal uterus, uterus with flat fundus, uterus with septum, heart-shaped uterus (uterus bicornis).

Hormonal disorders

Imbalances in thyroid hormones, low progesterone levels, and polycystic ovary syndrome (PCOS) are among the most common hormonal disorders causing miscarriage. A comprehensive hormone status check that also takes into account all thyroid hormones and antibodies quickly shows which of your hormones are in the normal range.

When does the underlying risk of miscarriage increase?

The likelihood of a miscarriage increases with the age of the pregnant woman because the risk of chromosomal disorders also increases with age. At the age of 32, the risk of miscarriage is approximately 13 percent. Afterward, it increases significantly from year to year. Women at the age of 40 have a 40 percent risk of having a miscarriage.

pregnancy chances miscarriage

Fig.: Pregnancy chances per age and cycle (turquoise) versus miscarriage risk per age and pregnancy (pink).

The risk of miscarriage also increases with the number of previous miscarriages. After three miscarriages – called recurrent pregnancy loss by doctors – the risk of another miscarriage is more than 50 percent. However, I wouldn’t wait that long to see a doctor. If you’ve miscarried twice, it makes sense for you to get a comprehensive check-up. Please reach out to me if you’re uncertain about what to do first. You can reach me at silvia@fertinesse.com.


The ESHRE Guideline Group on RPL: ESHRE guideline: recurrent pregnancy loss. Human Reproduction Open, Volume 2018, Issue 2, 2018.

Empson MB et al: Prevention of recurrent miscarriage for women with antiphospholipid antibody or lupus anticoagulant. Cochrane Database of Systematic Reviews 2005, Issue 2.

Nybo Andersen AM et al: Maternal age and fetal loss: population based register linkage study. BMJ 2000;320:1708-12.

Tempfer CB et al: A combination treatment of prednisone, aspirin, folate, and progesterone in women with idiopathic recurrent miscarriage: a matched-pair study. Fertil Sterile. 2006 Jul;86(1):145-8. Epub 2006 May 23.