The causes of pregnancy loss are categorized as chromosomal, anatomic, immunologic, infectious, egg quality, and unknown. Unfortunately, up to half of all patients with recurrent pregnancy loss have an unknown cause for their recurrent miscarriages.
Chromosomal abnormalities can be carried by one or both of the parents and passed on to the developing fetus, which could cause a miscarriage. These abnormalities are only detectable in the parents by a blood test, and are not correctable. However, once the chromosome abnormalities are detected, one or both prospective parents can go through genetic counseling to correctly assess their chances of a successful pregnancy.
Additionally, it is possible to perform preimplantation genetic diagnosis (PGD) in most cases. While not always 100 percent successful, embryos can be tested for the known genetic abnormality after performing in vitro fertilization. Only embryos that are chromosomally normal are then transferred to the uterine cavity in order to attempt to achieve a pregnancy that is unaffected by the chromosomal abnormality.
Anatomic causes of pregnancy loss include uterine and cervical abnormalities. For instance, if the uterus contains a septum (wall) within its cavity, embryo implantation will be difficult and pregnancy loss will likely continue. Uterine fibroids and scarring from previous surgeries can also cause miscarriage. However, these conditions are treatable through surgery, which would greatly increase the likelihood of carrying a pregnancy full term.
Anatomic abnormalities are also seen in women who were exposed to diethylstilbestrol (DES) as developing fetuses. Unfortunately, these abnormalities cannot be corrected, but steps to increase chances of a full term pregnancy can be taken for women who were exposed to DES.
Surgical correction offers a vastly improved prognosis for women with anatomic causes of pregnancy loss. For example, if a patient has a uterine septum, her chances of having a miscarriage without therapy are 70 percent. Once corrected, however, her chance of miscarriage returns to that of the unaffected population.
Although somewhat controversial as a cause of miscarriage, immunologic problems involving the presence of antibodies like those seen in women with rheumatologic disease (such as lupus or rheumatoid arthritis) may be related to pregnancy loss. Evidence has shown that treatment with low-dose aspirin and heparin may improve pregnancy outcomes in women with these antibodies. This type of therapy for autoimmune factors has approximately a 60 percent likelihood of a successful pregnancy.
Cervical and uterine infections may also increase the chance of pregnancy loss. Fortunately, infections are easily diagnosed with a cervical culture and easily treated with oral antibiotics.
As women age, egg quality continually deteriorates. Additionally, some women seem to experience accelerated loss of good quality eggs. In both circumstances, poor egg quality may be associated with an increased rate of miscarriage. For this reason, fertility providers will frequently recommend that women undergo testing for ovarian reserve on the second or third day of their menstrual cycle. Ovarian reserve testing consists of blood testing on the third day of the cycle and an ultrasound to count the number of antral (resting) follicles. These tests can help predict whether a woman has had significant loss of good quality eggs.
Approximately 50 percent of couples who have had two or more pregnancy losses will have no identifiable cause. In these cases they should not pursue treatment.
Research shows that couples who have experienced previous miscarriages have approximately a 60 percent to 70 percent likelihood of success with the next pregnancy. This means that failure to identify the problem does not imply a hopeless situation. On the contrary, without a known cause of their pregnancy loss, couples actually have an excellent chance of a successful pregnancy in the future.