Miscarriage, defined as the spontaneous loss of a pregnancy before 20 weeks of gestation, is a common experience, affecting an estimated 10% to 25% of known pregnancies. Many miscarriages occur very early, sometimes before a person even realizes they are pregnant. The emotional impact of pregnancy loss can be substantial, often leading to feelings of grief, sadness, and even deep guilt. Individuals often seek to understand why a miscarriage occurred, prompting questions about potential underlying causes, including whether genetic factors play a role.
Common Causes of Miscarriage
The majority of miscarriages result from factors that are not inherited. Over half of early pregnancy losses, particularly those in the first trimester, are due to spontaneous chromosomal abnormalities in the developing embryo. These errors, such as an extra or missing chromosome (aneuploidy), typically arise randomly during egg or sperm formation, or early embryonic cell division. Trisomy, an extra copy of a chromosome, is the most frequently observed abnormality, with trisomy 16 being a common example.
Beyond chromosomal issues, other non-hereditary factors can contribute to miscarriage. These include structural problems with the uterus, such as a septate uterus, or hormonal imbalances. Lifestyle factors like smoking and alcohol consumption, or chronic medical conditions such as uncontrolled diabetes or thyroid dysfunction, can also increase the risk.
The Hereditary Connection
While most miscarriages are not inherited, a genetic link can exist in specific situations. One notable hereditary cause involves inherited chromosomal rearrangements in a parent, such as a balanced translocation. In a balanced translocation, genetic material is rearranged but not gained or lost, so the carrier parent is typically healthy. However, if passed to an embryo, it can result in an unbalanced translocation, leading to missing or extra chromosomal material that often causes miscarriage.
These inherited translocations are found in approximately 3-5% of couples experiencing recurrent miscarriages. Beyond chromosomal rearrangements, certain single-gene disorders, like inherited blood clotting disorders (thrombophilias) or rare genetic syndromes, can also increase miscarriage risk. Though less common than sporadic chromosomal abnormalities, these inherited factors are important to identify, especially with recurrent miscarriages.
When Miscarriages Recur
Recurrent pregnancy loss (RPL) is defined as two or more consecutive miscarriages. This pattern prompts a comprehensive investigation into potential underlying causes, suggesting a persistent factor. While many recurrent miscarriages have no identifiable cause, repeated losses increase the likelihood of discovering an inherited genetic issue or other ongoing factors.
A parental balanced chromosomal translocation is identified in about 5% of recurrent miscarriages. Other factors investigated in RPL cases include uterine abnormalities, autoimmune conditions like antiphospholipid syndrome, and hormonal or metabolic disorders. Identifying these causes is crucial, as some recurrent losses may have targeted interventions to improve chances of a successful future pregnancy.
Genetic Counseling and Testing
For individuals or couples concerned about a hereditary component to miscarriage, genetic counseling is an important first step. Genetic counselors assess family history, discuss risks, and explain testing options. They can determine if a parent is a carrier of a balanced chromosomal rearrangement through karyotyping, a blood test analyzing chromosome structure and number.
Genetic testing can also be performed on miscarriage tissue, known as products of conception. This testing, often using chromosomal microarray analysis, identifies chromosomal abnormalities in the embryo, explaining the loss. Understanding the genetic landscape, whether in parents or miscarriage tissue, informs future family planning and guides discussions about reproductive options like in vitro fertilization with preimplantation genetic testing.