The major cause of an early miscarriage is probably a genetic (inherited) factor. An estimated 50 to 60 percent of all first trimester miscarriages of a single fetus (not twins or more) show evidence of genetic defects. The most common genetic defect resulting in miscarriage is an abnormal number or structure of chromosomes. If it’s determined that a pregnancy loss is due to a chromosomally abnormal fetus, there’s a greater chance that a subsequent pregnancy will also be abnormal. However, if the chromosomal examination of the fetus is normal, there’s a reduced chance that a subsequent pregnancy will be chromosomally abnormal.
Genetic Tests
Karyotyping
To determine whether there’s a genetic cause for repeated pregnancy loss, physicians may order a karyotype on the fetal tissue (which is generally obtained during a D&C) and on blood from both parents. If the karyotype is abnormal, there’s usually no therapy available, but the information may help to explain recurrent pregnancy loss for these couples.
In about 5 percent of cases, a chromosomal abnormality is found in one of the parents. If both parents have a normal karyotype, it’s likely that the miscarriage was a chance event and the couple should feel comfortable continuing to try to have a baby. In cases of abnormal karyotypes, genetic counseling to discuss the degree of risk may be recommended.
Birth Defects
Chromosomal analysis may also be recommended to couples who have had a child with multiple congenital defects (birth defects), or who have a history of one or more pregnancies ending in fetal or newborn death. Chromosomal problems found in these couples often involve structural changes in the chromosomes.
In cases where genetic abnormalities will lead to continued pregnancy losses, the couple should discuss treatment options with their physician. Options may include continuing efforts to have a baby using their own eggs and sperm, using donor eggs or a surrogate mother (if the woman has the genetic problem), or using donor sperm (if the man has the genetic problem).