Pathology Of Pregnancy
- There is a high rate of fetal loss in early pregnancy, and many early miscarriages are subclinical.
- Clinical miscarriage is usually the result of chromosomal abnormalities .
- The chorionic villi of the immature placenta may be oedematous (hydropic change), or the stroma may be fibrotic, which is an involutional change following fetal death.
- Characterised by swollen chorionic villi and trophoblastic hyperplasia
- Associated with high hCG levels
- Partial mole: triploid karyotype; fetus may be present
- Complete mole: 46XX karyotype; no fetus
- May be complicated by choriocarcinoma
- Hydatidiform mole is a disorder of pregnancy affecting approximately 1 in 1000 pregnancies in the Western world and is much commoner in the Far East.
- It is characterised by swollen, oedematous chorionic villi, trophoblastic hyperplasia and the irregular distribution of villous trophoblast.
- Macroscopically, the placenta appears to be composed of multiple cystic, 'grape-like' structures.
- A hydatidiform mole usually grows faster than a normal pregnancy, and the patient may present either with a 'large for dates' pregnant uterus, or with bleeding in early pregnancy.
- The partial mole is triploid, and may not be diagnosed clinically but only identified histologically in miscarriage material.
- Most contain one maternal and two paternal haploid sets of chromosomes, with all three sex chromosome patterns possible (XXY, XXX and XYY).
- It must be remembered, however, that not all triploids are partial moles.
- A fetus may be present and only a proportion of the villi abnormal; the rest may be fibrotic or may simply be hydropic without trophoblastic hyperplasia.
- Stromal vessels are present.
- The chromosomal constitution of the complete mole is androgenetic (i.e. of paternal origin), characteristically 46XX, and is probably due to the fertilisation of an 'empty' ovum by a spermatozoon carrying an X chromosome which is then reduplicated.
- Grossly, the placenta is obviously abnormal with swollen villi.
- Histologically, the oedema is confirmed; there is an absence of stromal vessels and circumferential trophoblastic hyperplasia affecting all villi.
- The constituent trophoblast may show varying degrees of cytological atypia.
The importance of correctly diagnosing hydatidiform mole is that, in a small number of cases, the disorder may be complicated by persistent trophoblastic disease.
This term encompasses two main pathological entities with similar clinical manifestations, diagnosed by persistently elevated or rising urinary hCG levels following evacuation of molar tissue.
- Invasive mole; chorionic villi are present within the myometrium and myometrial vessels. The main complication is uterine perforation.
- Choriocarcinoma; this is a rare, malignant neoplasm of trophoblast with a propensity to systemic metastasis.
- Although there is usually a preceding history of hydatidiform mole, choriocarcinoma may follow a miscarriage or very rarely an apparently normal pregnancy. It is more common in the Far East and, without treatment, has a high mortality. A biphasic pattern of invading cyto- and syncytiotrophoblast is the characteristic appearance of this tumour.
- Cases of hydatidiform mole are monitored by estimation of the serum and urinary hCG. If the level rises, or does not fall, then the patient will receive chemotherapy irrespective of the precise pathological diagnosis.
There are three main causes of post-partum haemorrhage:
- Retained chorionic villi
- Inadequate involution of placental bed vessels.
- Retained chorionic villi are unusual after normal pregnancy, but are more common following miscarriage or termination of pregnancy.
- Normally, after parturition, the myometrial segments of the uteroplacental spiral arteries are left behind, and rapidly undergo thrombosis to prevent torrential haemorrhage.
- Other involutionary changes then take place, and over the course of a few weeks the vessels resume their non-pregnant appearance.
- However, in a substantial number of cases of post-partum haemorrhage, the vessels are seen to be still distended and only partially thrombosed, so-c alled inadequate involution
- Pregnancy outside uterine cavity
- Fallopian tube is commonest site
- Leads to pain and haemorrhage when it ruptures
- Pregnancy-associated changes in endometrium
- An ectopic pregnancy is the occurrence of pregnancy outside the uterine cavity; its incidence is increasing.
- Occasionally, there is evidence of a fallopian tube abnormality such as chronic inflammation. The apparently increasing incidence of ectopic pregnancy may be related to increasing tubal infection.
- In most cases, however, there is no obvious cause, and a functional defect in tubal transport is assumed.
- The presenting symptoms are due to the physical expansion of the developing pregnancy within the limited space of the tube.
- Thus pain, with or without rupture, and haemoperitoneum are the commonest presenting features.
- In most cases, the pregnancy and fetus per se are not abnormal, and the same physiological changes associated with implantation can be seen in the fallopian tube as are seen in the uterus.
- The finding of pregnancy-associated changes in the endometrium in the absence of trophoblast or a fetus should always alert the possibility of an ectopic pregnancy (Arias-Stella phenomenon).