Causes of Abortion | Reasons for Abortion

Causes of Abortion:

1. ovular or fetal

2. maternal environment

3. paternal factor

4. unknown

ovo-fetal factors (60%)

(a) the ovo-fetal factors usually operate in early fetal wastage. Meticulous histological and cytogenetic study of the abortus reveals gross defects in the ovum or the fetus. The defects include

  • malformation
  • blighted ovum (ovum without embryo)
  • death or disease of the fetus often precedes the expulsive action of the uterus.

(b)Interference with the circulation in the umbilical cord by knots, twists or entanglements may cause death of the fetus and its expulsion.

(c)Low attachment of the placenta or faulty placental formation (circumvallate) may interfere with placental circulation.

(d)Twins or hydramnios (acute)  by rapidly stretching the myometrium may cause abortion.

 Maternal factors (15%)

maternal factors usually operate in late abortion.

(a) Maternal illness:

  • Infection: viral infection especially of rubella and cytomegalic inclusion disease produces congenital malformations and abortion. The viruses of hepatitis, parvovirus, influenza, have got lethal action on the fetus causing its death and expulsion. Parasitic (malaria) and protozoal infection (toxoplasmosis) may produce abortion if contracted in early pregnancy. Hyperpyrexia may precipitate abortion by increasing uterine irritability.
  • Maternal hypoxia and shock: acute or chronic disease, heart failure, severe anaemia or anaesthetic complications may produce anoxic state which may precipitate abortion. Severe gastroenteritis or cholera which is prevalent in the tropics is often an important cause.
  • Chronic illness: hypertension, chronic nephritis and chronic wasting disease are responsible for late abortion by producing placental infarction resulting in fetal anoxia.
  • Endocrine factor: an increased association of abortion is found in conditions of hypothyroidism, hyperthyroidism and diabetes mellitus. Inadequate corpus luteal state is consider to be related with unsatisfactory ovular growth and development and hence its expulsion.

(b) Trauma:

  • Direct trauma: on the abdominal wall by blow or fall may be related to abortion. But fortunately except in abortion prone women, pregnancy remains undisturbed.
  • Psychic: emotional upset or change in environment may lead to abortion by affecting the uterine activity.
  • In susceptible individual, even a minor trauma in the form of a journey along rough road, internal examination in early months or eliciting Hegar’s sign or sexual intercourse in early months is rough to excite abortion.
  • Amniocentesis, chorion villus sampling or abdominal surgery in early months may cause abortion.

(c) Toxic agents: environmental toxins like lead, arsenic, anaesthetic gases, tobacco, caffine, alcohol, radiation in excess amount increase the risk of abortion. Drugs used for epilepsy or antimalarial preparations (quinine) are not so much harmful when used in therapeutic doses so as to cause abortion.

(d) cervico-uterine factors: these are related to the second trimester abortions.

  • Cervical incompetence: either congenital or acquired is one of the commonest causes of midtrimester and recurrent abortions.
  • Congenital malformation of the uterus: in the form of bicornuate or septate uterus may be responsible for midtrimester or recurrent abortion.
  • Uterine tumour: (fibroid) especially of the sub mucous variety might be responsible not only for infertility but also for abortion due to distortion of the uterine cavity and increased uterine irritability.
  • Retroverted uterus: is not responsible for abortion but its association might be due to its failure to rectify between 12-14weeks due to adhesions or due to trauma during sexual intercourse or it could be due to disturbance in uterine vascularity.

(e)Immunological: presence of autoimmune factor like lupus anticoagulants and antiphospholipid antibodies increase the risk of abortion.

(f)  Blood group incompatibility: incompatible ABO group mating may be responsible for early pregnancy wastage and often recurrent but Rh incompatibility is a rare cause of death of the fetus before 28 weeks. Couple with group ‘A’ husband and group ‘o’ wife have got higher incidence of abortion.

(g)Premature rupture of membranes: inevitably leads to abortion.

(h)Dietetic factors: deficiency of folic acid or vitamin E is often held responsible.

Paternal factors

Defective sperm, contributing half of the number of the chromosomes to the ovum, may result in abortion, but it is difficult to prove. However, some women who abort habitually may have normal pregnancies following marriage with a different man.

Unknown (25%)

Inspite of the numerous factors mentioned, it is indeed difficult, in a majority, to pinpoint the cause of abortion in clinical practice. Too often, more than one factor is present.