Miscarriage and abortion

Chapter 11 Miscarriage and abortion



Abortion or miscarriage is defined as the expulsion of a fetus before it reaches viability. Because of different definitions of viability in different countries, the World Health Organization (WHO) has recommended that a fetus is considered potentially viable when the gestation period has reached 22 weeks or more, or when the fetus weighs 500 g or more. As the term abortion does not differentiate between spontaneous and induced abortion the term miscarriage is widely preferred, abortion being used when the pregnancy is deliberately terminated before fetal viability. Most miscarriages occur naturally between the sixth and 10th weeks of pregnancy.


Data from several countries estimate that between 10 and 20% of clinically diagnosed pregnancies end in miscarriage. Miscarriage is more frequent among women over the age of 30 and increases further among women over the age of 35; the risk being nine times greater than for women aged 20–29. Paternal age over 40 also increases the risk, albeit not as strongly as maternal age. The risk also increases in frequency with increasing gravidity: 6% of first or second pregnancies terminate as a miscarriage; with third and subsequent pregnancies the rate increases to 16%.



AETIOLOGY OF SPONTANEOUS MISCARRIAGE


The causes of miscarriage are:









MECHANISMS OF MISCARRIAGE


The immediate cause of miscarriage is the partial or complete detachment of the embryo by minute haemorrhages in the decidua. As placental function fails uterine contractions begin, and the process of miscarriage is initiated. If this occurs before the eighth week the defective embryo, covered with villi and some decidua, tends to be expelled en masse (the so-called blighted ovum), although some of the products of conception may be retained either in the cavity of the uterus or in the cervix. Uterine bleeding occurs during the expulsion process.


Between the eighth and 14th weeks the above mechanism may occur or the membranes may rupture, expelling the defective fetus but failing to expel the placenta, which may protrude through the external cervical os or remain attached to the uterine wall. This type of miscarriage may be attended by considerable haemorrhage.


Between the 14th and 22nd weeks the fetus is usually expelled followed, after an interval, by the placenta. Less commonly the placenta is retained. Usually bleeding is not severe, but pain may be considerable and resemble a miniature labour.


It is clear from this description that miscarriage is attended by uterine bleeding and pain, both of varying intensity. Although miscarriage is the cause of bleeding per vaginam in early pregnancy in over 95% of cases, less common causes, such as ectopic gestation, cervical bleeding from the everted cervical epithelium or from an endocervical polyp, hydatidiform mole, and, rarely, cervical carcinoma, must be excluded.



VARIETIES OF SPONTANEOUS MISCARRIAGE


For descriptive purposes the miscarriage is classified according to the findings when the woman is first examined, but one kind may change into another if the aborting process continues. If infection complicates the miscarriage, the term septic miscarriage is used. The various types of miscarriage are shown in Figure 11.1 and each will be considered separately later.





Inevitable, incomplete and complete miscarriage


Miscarriage becomes inevitable if uterine bleeding is associated with strong uterine contractions that cause dilatation of the cervix. The woman complains of severe colicky uterine pains, and a vaginal examination shows a dilated cervical os with part of the conception sac bulging through. Inevitable miscarriage may follow signs of threatened miscarriage or, more commonly, starts without warning.


Soon after the onset of symptoms of inevitable miscarriage, the miscarriage occurs either completely, when all the products of conception are expelled, or incompletely when either the pregnancy sac or the placenta remains, distending the cervical canal. In most cases the miscarriage is incomplete. Unless the doctor has been able to inspect all the material expelled from the uterus, or has had an ultrasound examination that shows an empty uterus (or one containing less than 10 mm of tissues or blood clots), the miscarriage should be considered incomplete. This is treated by curettage; an alternative is to give misoprostol 400 μg 4-hourly for three doses or 800 μg as a single dose which will achieve a 60–80% complete evacuation of the uterus.


Jun 15, 2016 | Posted by in OBSTETRICS | Comments Off on Miscarriage and abortion

Full access? Get Clinical Tree

Get Clinical Tree app for offline access