SPONTANEOUS ABORTION(mircarriage)=  A) incidence= 10-20%. 75% abortions occur b4 16th wk n of these, abt 75% occur b4 8th wk of pregnancy.
B)ETIOLOGY= 1-GENETIC FACTORS= a) chromosomal abnormality like autosomal trisomy commonest.  b)most common trisomy is trisomy 16.  Polyploidy observed in 22% of abotuses.   c)monosomy- 20% d)structural chromosomal rearrangements-2-4%..e)other- mosaib, double trisomy- 4%.  2-ENDOCRINE N METABOLIC FACTORS=..a)luteal phase defect..b)deficient progesterone secretion..c)thyroid abnormalities-hypo n hyperthyroidism.. d)diabetes mellitus... 3-ANATOMICAL ABNORMALITIES= a)cervico uterine factors- these r related to 2nd trimester abortions., such as  cervical incompetence,.,congenital malformation of uterus,  4-INFECTIONS= a)transplacental fetal infections occur.. They could b..*)viral-rubella, cytomegalo, hiv..*) parasitic- toxoplasma, malaria..*)bacterial-chlamydia, brucella.. 5- IMMUNOLOGICAL DISORDERS= a)autoimmune disease- cause miscarriage in 2nd trimester. *)antibodies resoponsible r- anti-nuclear antibodies, anti phospholipid antibodies.. b)alloimmune disease... c) maternal medical illness.-cyanotic heart disease, haemoglobinopathies... 6- BLOOD GROUP INCOMPATIBILITY=  incompatible ABO group matings  r responsible.. Rh incompatibility is rare cause.. 7= PEMATURE RUPTURE OF MEMBRANE= a)paternal factors- sperm chromosomal anomaly.. b) inherited thrombophilia- protein 'C' resistance is commonest cause for it.   8-ENVIRONMENTAL FACTORS= a)cigarette smoking- increases risk due to formation of carboxy Hb n decreased oxygen transfer to fetus. b) alcohol..c) x-irradiation n antineoplastic drugs...d) contraceptive agents-IUD.  e)drugs, chemicals, noxious agents.. 9-UNEXPLAINED= such as increased maternal age, no. of previous abortions.
 C)MECHANISM OF ABOSTION= 1-  in early wks, death of ovum occurs first followed by expulsion.   2- in later wks, maternal environmental factors r involved leading to expulsion of fetus.  *) b4 8 weeks= ovum is expelled out intact. Sometimes., d external os fails to dilate so tht entire mass is accommodated in dilated cervical canak n is called cervical abortion. *) 8-14 weeks= expulsion of fetus commonly occurs leaving behind placenta n membranes.   Part of it may a partially separated wid brisk haemorrhage or remains totally attached to d uterine wall.          *) Beyond 14th week- process of expulsion is similar to tht of 'mini labour'.   Fetus is expelled out first followed by expulsion of d placenta after varying interval.. 

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