Human reproduction is extraordinarily inefficient. Pregnancy loss rates are remarkably high at all ages, with 10% to 15% of all clinically recognized pregnancies undergoing spontaneous abortion even in women during their peak fertility years (between 20 and 30 years old). The rate of miscarriage is age related, rising to over 50% in women older than age 40.
Many pregnancies are lost so early in development that no gestational sac is ever visualized on sonogram. This type of pregnancy loss is called a biochemical pregnancy. In most cases, once fetal cardiac activity is visualized on ultrasound, the miscarriage rate drops to less than 5%. In women older than age 40, however, the pregnancy loss rate remains 25% or greater even after visualization of cardiac activity. A pregnancy that stops developing in the absence of any bleeding is called a missed abortion. Remember that the medical term “abortion” refers to any pregnancy loss, either spontaneous or induced. Miscarriage is a lay term that is used to refer to a spontaneous abortion. Although most pregnancy losses occur during the first trimester, adverse outcomes can occur at any gestational age.
There are many ways to manage a non-viable pregnancy. A surgical procedure called a dilation and curettage (D&C) can quickly resolve an abnormal pregnancy. In addition, the tissue from a D&C can be sent for genetic analysis to determine if the loss was genetically abnormal. Some Ob/Gyns will administer medication to induce a miscarriage using oral/vaginal drugs to initiate the miscarriage process. Finally, some physicians prefer to let nature take its course and await a spontaneous loss.