This is a condition when a woman has 2 or more clinical pregnancy losses (miscarriages) before the pregnancies reach 20 weeks. Losses are classified by when they occur. Loss of a “clinical pregnancy” is diagnosed by a health-care provider using ultrasound. In most cases, a pregnancy can be seen with ultrasound as early as 5-6 weeks’ gestational age (or 1-2 weeks after a missed period). A “biochemical pregnancy” loss is one that has been detected only by urine or blood hormone testing before disappearing. Biochemical losses are not usually included in making an RPL diagnosis.
Causes: There are a variety of reasons why women may have more than one miscarriage:
- Genetic : Many early miscarriages (the ones that happen in the first 3 months of pregnancy) are due to genetic abnormalities in the embryo or fetus. Normally, there are 46 chromosomes that contain the genes for normal development. Many early miscarriages happen because the fetus has an extra chromosome or one is missing. For example, babies with Down syndrome have 47 chromosomes. Chromosome abnormalities occur for no known reason in up to 60% of first-trimester miscarriages. Genetic abnormalities typically do not allow development into a healthy baby. As women age, the miscarriage risk due to these genetic abnormalities increases — from 10%-15% in women younger than 35 years old to more than 50% in women over 40 years old.
- Anatomic : A problem with the shape of a woman’s uterus might be a cause for pregnancy loss. Causes for abnormal shape of the uterus can be genetic or exposure before birth to medications such as diethylstilbestrol (DES).
Other anatomic causes include having a band of tissue inside the uterus, called a septum. This can make the inside of the uterus too small. Women born with a septum may have more frequent miscarriages. Fibroids, benign muscle tumors of the uterus, are also common. These can lead to miscarriages if they grow into or near the uterine cavity.
- Lifestyle/Environmental : Smoking increases the risk for RPL. Using certain recreational drugs, such as cocaine, can also lead to miscarriage. Being overweight has been linked with RPL as well as other pregnancy complications. Excessive alcohol or caffeine intake might be linked with RPL.
- Medical : Untreated medical conditions, such as thyroid disease or diabetes, can increase the risk for miscarriage. Abnormalities of the immune system or blood-clotting system (thrombophilia) can also cause RPL.
In over half of RPL cases, doctors cannot find the cause for losses. However, many of these may be due to genetic abnormalities.