Abortion: Types and Incidence

Abortion

• Abortion is the expulsion of a fetus from the uterus before it reaches viability (around 20th week of gestation).

Spontaneous Abortion

• Spontaneous abortion is a termination of pregnancy without any action taken by the woman or another person.
• Incidence of spontaneous abortion is approximately 18% to 31% of all pregnancies.
• Most pregnancies (50% to 70%) are lost during the first trimester, many of which may occur before implantation or during the first month after the last menstrual period.

Causes of Spontaneous Abortion

• Chromosomal abnormalities (50%-60%) resulting in anembyonic pregnancies.
• Maternal infections such as Syphilis, Listeriosis, Toxoplasmosis, Brucellosis, Rubella, and Cytomegalic Virus.
• Maternal endocrine disorders such as Hypothyroidism, Diabetes, and decreased Progesterone.
• Anatomic defects of the uterus, uterine septum, or cervical incompetence.
• Heavy alcohol consumption and heavy smoking may contribute to spontaneous abortion.
• Teratogen drugs and radiation (cancer chemotherapy) can also cause spontaneous abortion.

Pathophysiology of Spontaneous Abortion

• Embryonic death occurs, leading to a decrease in human chorionic gonadotropin (hCG) and progesterone and estrogen levels.
• The uterine decidua is sloughed off, resulting in vaginal bleeding, and the embryo/fetus is expelled.

Classification of Spontaneous Abortion

• Threatened Abortion: unexplained bleeding, cramping, or backache indicating that the fetus may be in jeopardy, with bleeding persisting for days and the cervix remaining closed.
• Inevitable Abortion: abortion is usually inevitable when membranes rupture and the cervix dilates, resulting in excessive bleeding or infection.
• Incomplete Abortion: some but not all of the products of conception are expelled from the uterus, with active uterine bleeding and severe abdominal cramping.
• Complete Abortion: all products of conception are expelled from the uterus, with uterine contractions and bleeding subsiding, and the cervix closing.
• Missed Abortion: the fetus dies in utero but is not expelled, resulting in uterine growth ceasing, breast changes regressing, and a negative pregnancy test.
• Recurrent or Habitual Abortion: abortion occurs consecutively in three or more pregnancies, with causes including genetic or chromosomal abnormalities, reproductive tract anomalies, and inadequate luteal phase.