How does a miscarriage occur?

A miscarriage is usually caused by a combination of medical factors. Genetic abnormalities in the embryo may play a role. According to the Dutch Society of Obstetrics and Gynecology, this is often due to an error in the distribution of chromosomes during fertilization. This typically occurs by chance and is, in most cases, not hereditary.

In addition, the quality of the menstrual cycle plays an important role in both the occurrence and maintenance of a pregnancy. A disrupted cycle may indicate underlying hormonal problems that increase the risk of miscarriage. For example, poor egg quality may lead to chromosomal abnormalities during conception and problems with implantation. Inadequate ovulation may result in lower progesterone production, a hormone essential for supporting the uterine lining. A shortened luteal phase (the period after ovulation) may also prevent proper implantation or development of a pregnancy.

By closely monitoring the cycle and measuring hormone levels at specific times, these abnormalities can be identified and treated in a targeted way.

In addition to hormonal and cycle-related factors, structural abnormalities of the uterus may also play a role. These include congenital malformations, fibroids (myomas), or adhesions that can interfere with implantation or the growth of a pregnancy.

Furthermore, immunological and clotting disorders, such as antiphospholipid syndrome, are known causes. These can disrupt blood flow to the placenta. In cases of recurrent miscarriage, immunological factors are also considered, where the immune system may play a role.

Other underlying conditions such as thyroid disorders, diabetes, or polycystic ovary syndrome (PCOS) can also increase the risk of miscarriage. For this reason, we do not look at individual symptoms in isolation, but consider the overall picture of immunological factors, hormonal regulation, and cycle quality.

In modern reproductive medicine, increasing attention is also being given to the microbiome of the reproductive system. This refers to the bacterial composition of the vagina and the uterine lining. International research, including the ReceptIVFity cohort studies at Erasmus MC in Rotterdam, suggests a possible link between a healthy environment and improved implantation.

Lifestyle also plays a crucial role. Factors such as smoking, alcohol consumption, overweight, sleep deprivation, and chronic stress can negatively affect both fertility and pregnancy outcomes. A healthy lifestyle — including sufficient rest, balanced nutrition, and stress reduction — helps restore hormonal balance and creates an optimal environment for a developing pregnancy.