Anatomical abnormalities of the uterus: This includes conditions such as a septate uterus, bicornuate uterus, or uterine fibroids, which can interfere with implantation or growth of the embryo, leading to recurrent miscarriages. Uterine anomalies are a common cause of recurrent pregnancy loss.

Hormonal imbalances: Conditions like polycystic ovary syndrome (PCOS), thyroid disorders, or luteal phase defect can affect ovulation, fertilization, or implantation, leading to recurrent pregnancy loss.
Immunological disorders: Antiphospholipid syndrome (APS) is an autoimmune disorder that can cause blood clots in the placenta, leading to miscarriage. Other immunological factors, such as an overactive immune response, can also contribute to recurrent pregnancy loss.
Genetic factors: Chromosomal abnormalities in either partner, such as balanced translocations, can increase the risk of recurrent miscarriage.
Infections: Certain infections, like listeriosis or toxoplasmosis, can cause miscarriage, although they are less common causes of recurrent pregnancy loss.

Antiphospholipid syndrome (APS): Although mentioned under other likely diagnoses, APS is critical to identify due to its potential for severe complications, including thrombosis and fetal loss. Missing this diagnosis could lead to significant morbidity and mortality.
Thyroid dysfunction: Untreated thyroid disease can have serious consequences for both mother and fetus, including miscarriage, preterm birth, and fetal growth restriction.

Molecular and genetic abnormalities: Rare genetic conditions, such as embryonic mosaicism or mutations affecting implantation, can cause recurrent pregnancy loss.
Uterine leiomyosarcoma: A rare type of cancer that can cause recurrent miscarriages, although it is extremely uncommon.
Inherited thrombophilias: Conditions like factor V Leiden or prothrombin gene mutation can increase the risk of blood clots and, consequently, recurrent pregnancy loss, but are less frequently encountered as a primary cause.