The term “abortus” refers to the termination of a pregnancy within biological and medical contexts. This event can occur through natural processes, known as spontaneous pregnancy loss or miscarriage, or as a result of medical intervention. Understanding the biological underpinnings of “abortus” provides insight into human reproduction and the factors that can disrupt them.
What “Abortus” Means in Biology
The Latin term “abortus” denotes the expulsion of an embryo or fetus from the uterus before viability, typically before 20 weeks of gestation or when the fetus weighs less than 500 grams. This term is often used interchangeably with “miscarriage” in clinical practice when referring to a spontaneous event. It signifies a pregnancy ending unintentionally, differentiating it from an induced termination, which involves deliberate actions.
Biological Reasons for Spontaneous Pregnancy Loss
Spontaneous pregnancy loss, or miscarriage, arises from various biological factors that disrupt fetal development and maternal support. Chromosomal abnormalities are the most frequent cause, accounting for 50-65% of all miscarriages, especially those occurring in the first trimester. These abnormalities, such as an abnormal number of chromosomes (aneuploidy), often lead to irregular development or halt embryo growth. For example, trisomies, where an embryo has an extra copy of a chromosome, represent about half of all chromosomal anomalies associated with miscarriage.
Hormonal imbalances can also contribute to pregnancy loss. For instance, insufficient progesterone levels, necessary to maintain the uterine lining and support early pregnancy, may be a factor. Certain maternal health conditions, such as uncontrolled diabetes, thyroid disorders, or autoimmune conditions like antiphospholipid syndrome, can increase the risk of spontaneous pregnancy loss.
Structural issues within the uterus, such as congenital uterine defects, fibroids, or intrauterine adhesions, can impede proper implantation and growth of the embryo. Additionally, infections caused by certain viruses, including cytomegalovirus, herpesvirus, parvovirus B19, rubella virus, or Zika virus, have been associated with an increased risk of pregnancy loss. Approximately one-fourth of cases have an undetermined cause.
Different Forms of Spontaneous Pregnancy Loss
Spontaneous pregnancy loss manifests in several distinct forms. A threatened miscarriage involves vaginal bleeding and sometimes cramping before 20 weeks of gestation, but the cervix remains closed and the pregnancy may continue.
An inevitable miscarriage indicates that the process of pregnancy loss is actively occurring and cannot be stopped. This is characterized by vaginal bleeding, often accompanied by cramping, and dilation of the cervix. The membranes may also be ruptured, and the expulsion of the products of conception is expected.
An incomplete miscarriage occurs when some, but not all, of the pregnancy tissue has been expelled from the uterus. The cervix remains dilated, and bleeding and cramping typically persist as the body attempts to clear the remaining contents. In contrast, a complete miscarriage involves the full expulsion of all pregnancy tissue, after which the cervix usually closes, and bleeding and cramping subside.
A missed miscarriage refers to a nonviable intrauterine pregnancy where the embryo or fetus has died, but no symptoms of expulsion, such as bleeding or cervical dilation, have occurred. The pregnancy tissue remains within the uterus, and the diagnosis is often made when a fetal heartbeat is not detected during an ultrasound. Another classification is an anembryonic pregnancy, also known as a blighted ovum, where a gestational sac develops but no embryo is visualized within it.
The Body’s Response to Spontaneous Pregnancy Loss
Following a spontaneous pregnancy loss, the body undergoes biological and physiological adjustments to return to a non-pregnant state. The uterus begins to contract to expel the remaining pregnancy tissue, which leads to cramping and vaginal bleeding. The intensity and duration of bleeding can vary, often being heavier than a typical menstrual period, and may include the passage of blood clots and tissue. This process of uterine contraction and expulsion can last from one to four weeks.
Hormonal shifts are a significant part of the body’s response. Levels of pregnancy hormones, such as human chorionic gonadotropin (hCG), estrogen, and progesterone, which were elevated to support the pregnancy, begin to decline rapidly. This sudden drop in hormone levels contributes to the resolution of early pregnancy symptoms like nausea or breast tenderness. As these hormone levels decrease, the body prepares to resume its regular menstrual cycle, which typically returns within a few weeks to a couple of months.
The physical recovery period involves the uterus gradually returning to its pre-pregnancy size, a process that can take several weeks. The body’s immune system also plays a role in clearing any remaining cellular debris. While the physical symptoms usually resolve within about six weeks, continued monitoring by a healthcare provider is important to ensure that all tissue has been expelled and to address any prolonged bleeding or signs of infection.