Chapter 13 Antepartum haemorrhage
Antepartum haemorrhage is defined as significant bleeding from the birth canal occurring after the 20th week of pregnancy. The causes and proportions of cases of antepartum haemorrhage are shown in Table 13.1. In fewer than 0.05% of cases the bleeding is due to a cervical lesion, such as a cervical polyp, or rarely, a cervical carcinoma.
Table 13.1 The incidence of the causes of antepartum haemorrhage
| INCIDENCE (%) | |
|---|---|
| Placenta praevia | 0.5 |
| Placental abruption | |
| Mild or indeterminate | 3.0 |
| Moderate grade | 0.8 |
| Severe grade | 0.2 |
| Cervical bleeding | 0.05 |
PLACENTA PRAEVIA
In this condition the placenta is implanted, either partially or wholly, in the lower uterine segment and lies below (praevia) the fetal presenting part. The extent of implantation may be minor, in which case vaginal birth is possible, or major, when it is not (Fig. 13.1).
Placenta praevia occurs in 0.5–2.0 % of all pregnancies, and accounts for 20% of all cases of antepartum haemorrhage. The incidence has increased between two- and threefold over the past 20 years. It is three times as common in multiparous women as in primiparae. The incidence increases with each previous caesarean section. The incidence in women who have not had a previous caesarean is 0.3%, after one is 0.8%, after two is 2.0%, and after three or more is 4.2%. The risk is also increased when a submucous fibroid is present.
The bleeding occurs when the lower uterine segment is increasing in length, and shearing forces between the trophoblast and the maternal blood sinuses occur. The first episode of bleeding occurs after the 36th gestational week in 60% of cases, between the 32nd and 36th weeks in 30%, and before the 32nd week in 10%.
Symptoms, signs and diagnosis
The bleeding is painless, causeless and recurrent. The presenting part is usually high and often not central to the pelvic brim. The diagnosis is made should an ultrasound image show that the placenta is praevia (Figs 13.2, 13.3).
If a routine ultrasound examination is made at 18 weeks the report may show that there is a low-lying placenta, but in over 85% the placenta will be normally situated by the time of delivery, as the lower uterine segment does not develop fully until late in the third trimester. A further ultrasound examination should be made at about the 34th week, or earlier if vaginal bleeding occurs.
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