A 38-year-old woman presents at 39 + 4 weeks gestation with severe abdominal pain and dark red blood loss of an estimated 100 ml vaginally. This is her first pregnancy and apart from gestational diabetes with polyhydramnios, there have been no other concerns regarding the pregnancy. On examination, she has a heart rate of 126 bpm. Her other vital signs are unremarkable. Her abdomen is tense and she appears in significant pain.

What is the most likely diagnosis?

Options:
explanation: Vasa praevia is a condition where foetal blood vessels lie against the internal cervical os and are unsupported by the placenta, making them particularly vulnerable to rupture during labour. The typical triad for vasa praevia is membrane rupture, painless vaginal bleeding and foetal bradycardia/death. Vasa praevia is more common in multiple gestations and in vitro fertilisation. The history given here is more in keeping with placental abruption due to painful bleeding with a tense uterus.
name: Vasa Praevia
label: d
answer: no
explanation: Uterine rupture is a reasonable diagnosis given the pain and shock. However, a more typical history would include a description or tearing pain, with midline abdominal tenderness and minimal blood loss vaginally. During a uterine rupture there can be amniotic fluid leakage into the abdominal cavity and there may be rapid foetal deterioration. Risk factors for uterine rupture include previous uterine surgery, such as C-section, which this patient has not had.
name: Uterine rupture
label: b
answer: no
explanation: This typically presents with an acute history of shortness of breath and cardiovascular collapse during or shortly after delivery. Disseminated intravascular coagulation may be present. There are risk factors for this, including advancing maternal age, cardiac disease and multiparity but its occurrence is unpredictable and not completely understood. Amniotic fluid and foetal components enter the maternal circulation, triggering a cascade of pulmonary vasoconstriction and disseminated intravascular coagulation. This patient is in shock but there is no evidence of coagulopathy, making placental abruption more likely.
name: Amniotic fluid embolism
label: e
answer: no
explanation: Placenta praevia refers to when the placenta lies low in the uterus, covering the cervix, and thus the path the foetus will have to take during labour in part or full. The bleeding in placenta praevia is typically painless and bright red, with a soft abdomen. The placenta may be palpable in the lower segment on examination. In this case, the patient has marked pain, a woody tense uterus and dark coloured blood, making a diagnosis of abruption more likely.
name: Placenta praevia
label: c
answer: no
explanation: The key features indicating placental abruption are the presence of a tense 'woody' uterus, dark red blood passed vaginally, pain and evidence of shock. In placental abruption, the external blood losses may be disproportionate to the degree of shock, as indicated in this case with only 100 ml of blood apparently lost but the presence of a significant tachycardia. This is because the blood mostly remains between the placenta and the uterine wall and so external losses can be minimal. Risk factors for placental abruption include maternal hypertension, trauma, polyhydramnios and cocaine use.
name: Placental abruption
label: a
answer: yes

Correct answer: a


Learning point: Placental abruption is a serious pregnancy complication where the placenta separates prematurely from the uterine wall, leading to bleeding, abdominal pain, and potential risk to both the mother and foetus.