USC Fertility

Causes of Pregnancy Loss

The causes of recurrent pregnancy loss can be difficult to determine

Recurrent pregnancy loss (RPL) is devastating for couples. Unfortunately, the causes of recurrent pregnancy loss is only determined in about 50% of couples.

Here are the different known causes of RPL. 


Genetic: Chromosomal abnormalities (aneuploidy) are the most common cause of spontaneous miscarriages. Aneuploidy, or having extra or too little chromosome copy numbers result in pregnancies that are abnormal and have no probability of survival. Most of the time the embryos won’t implant, but if they do they most commonly result in miscarriage. Aneuploidy risk increases with maternal age.

Women that have had 2-3 miscarriages in a row may just be having bad luck in that chromosomally abnormal embryos have resulted in miscarriage several times consecutively. The good news is that often times in the next pregnancy, the embryo will be chromosomally normal and a live birth will ensue.

Adults that are themselves healthy can be carriers of chromosome disorders and rearrangements that can be transmitted to their offspring. When this happens this can lead to loss of the pregnancy. Examples of these disorders are translocations, inversions and deletions involving any of the chromosomes.

Endocrine: Uncontrolled diabetes, thyroid disease, and high prolactin levels can increase a woman’s chance of miscarriage. When diagnosed with these disorders, women who receive treatment may improve their chance of successful pregnancy.

Women with polycystic ovary syndrome (PCOS) have a two-fold risk of miscarriage compared to women without PCOS.

Autoimmune: The autoimmune disorder, anti-phosphospholipid antibody syndrome, is another cause for pregnancy loss. Having miscarriages or more advanced pregnancy losses is part of the diagnostic criteria for this disorder. Thrombophilias (blood clotting disorders) are not well-established potential causes of RPL.

Anatomic: Uterine issues may contribute to RPL. Fibroids that protrude into the uterine cavity or distort the cavity shape can potentially increase the chance of miscarriage. Adhesions inside the uterus from previous surgery/procedures can cause an increased risk of miscarriage. Uterine polyps may also contribute to miscarriage. Congenital anomalies, such as a uterine septum, can lead to almost a 60% chance of miscarriage. All of these factors may impair the ability of the embryo to implant due to factors such as poor blood supply or limited space.

Other: Other factors that might contribute to RPL are cigarette use, alcohol (more than 3-5 drinks per week), excessive caffeine consumption (>3 cups per day), and obesity (BMI more than 30). Celiac disease and infections may also contribute to pregnancy loss, though the relationship is not clear.