Abortion is the extraction or expulsion of the embryo or fetus weighing 500g or less from its mother before it can survive alone. This 500g is usually attained by the fetus around 22 weeks of gestation. The products of abortion is called abortus.
The incidence of abortion may be difficult to find out but according to current study is about 10-20% of all clinical pregnancies end in abortion and another 10% are induced illegally. 75% of all abortion occur before the 16 weeks of gestation .
Abortion has been classified into several subgroups. The main one is spontaneous abortion or miscarriage (occur naturally) and the other one induced abortion (initiated artificially). Spontaneous abortion is of clinical important and is the one will be explained here.
Spontaneous abortion has been subdivided into several groups which are threatened, inevitable, complete, incomplete, missed and septic abortion. Each type will be explained in details separately in the following post.
The etiology/causes of spontaneous abortion is complex and difficult to find out. The following factor are important and with the positive association:-
Genetics-About 50% of all early spontaneous abortion occur due to chromosomes abnormalities in the conceptus. This include autosomal trisomy is the commonest one for about 50% and the commonest triosomy is 16 (30%). polyploidy 22% (presences of three or more haploid number of chromosomes) has been reported and the commonest one is triploidy. Other are monosomy and structural chromosomes rearrangement has been reported to cause miscarriage.
Endocrine and metabolic factors- deficient in progesterone hormone or poor uterine response to the progesterone is the cause. conditions like hypothyroidism or hyperthyroidism has association with abortion. Poorly or uncontrolled diabetic mellitus has been linked to result in miscarriage.
Anatomical abnormalities- cervical and uterine factors like cervical incompetence, congenital malformation of the uterus has been associated with pregnancies lose especially during the second trimester. Condition like uterine fibroid and uterine adhesion has positive effect on pregnancy loss because of reduced uterine volume, interfere with implantation, placentation and fetus growth.
Infections- infections such as viral infections ( rubella, cytomegalo and even HIV infection), bacterial infections ( chlamydia, syphilis, and others ), parasitic infections ( malaria, and toxoplasma) are hardly result in abortion before 20 weeks of gestation because of effective thickness of placental barrier.
Immunologic disorders- autoimmune disorder like antinuclear antibodies can cause miscarriage usually in the second trimester. Alloimmune disease may result into fetal rejection by maternal antibodies and hence miscarriage occur.Antifetal antibodies in case Rhesus isoimmunization where by the mother is rhesus negative and the fetus is rhesus positive can usually cause spontaneous abortion.
Other factors- maternal medical illness like cyanotic heart disease and hemoglobinopathy has been associated with early pregnancy loss. Premature rupture of membrane, cigarette smoking and alcohol used during pregnancy has increase the incidence of miscarriage.
Unexplained etiology- around 40-60% of all miscarriage cases has no know etiology despite all of the above explained factors. However the risk of miscarriage increase with maternal age. More than 20% of all pregnancies diagnosed using urine pregnancy test, are lost before the clinical diagnosed.
DR MWANDA.
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