Investigations

1st investigations to order

uterine ultrasound with colour flow Doppler analysis

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Result
Test

Ultrasound may be done transabdominally, transvaginally, translabially, or transperineally.[37] The American College of Radiology and the American College of Obstetricians and Gynecologists recommend transabdominal ultrasound as the preferred initial procedure for diagnosis of PP, advising that a transvaginal approach may be used if transabdominal examination is inconclusive or inadequate.[37][38] The Society of Obstetricians and Gynaecologists of Canada, the Royal College of Obstetricians and Gynaecologists, and the Society for Maternal-Fetal Medicine meanwhile recommend transvaginal ultrasound as the initial procedure, stating that it is more accurate for the diagnosis of PP, with a sensitivity of 88% and a specificity of 99%.[1][2][5]

There are no defined indications for the use of translabial or transperineal ultrasound, although transperineal examination may be useful in the presence of bulging or ruptured membranes.[37]

If PP is suspected, referral should be made for colour flow Doppler ultrasound to screen for placenta accreta spectrum.[4][36][41][48][49][50][51][52][53]

Alpha-fetoprotein (AFP) is usually offered routinely as part of triple or quadruple testing to screen for neural tube defects and other congenital abnormalities. If a second- or third-trimester PP is diagnosed in a woman with an abnormal AFP level, the index of suspicion for invasive placentation should be high and an ultrasound scan considered.[47]

If placenta accreta spectrum cannot be reliably excluded on ultrasound, MRI of the placenta should be obtained.[2][4][41]

Result

position of placenta; variable

FBC

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Result
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Haemoglobin usually decreases in pregnancy, and normal values vary with gestational age (may be as low as 100 g/L [10 mg/dL] in mid-pregnancy). Iron deficiency (and, in certain genetic groups, thalassaemia) commonly co-exists with pregnancy and may result in an even lower haemoglobin.

Women with significant haemorrhage may present with haemoglobin <100 g/L (<10 mg/dL).

Follow with serial FBCs (frequency depends on degree of bleeding).

Result

in acute bleeding, haemoglobin low for normal pregnancy values

type and cross-match

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Result
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Type and screen and cross-match for at least 4 units of packed red blood cells (and inform transfusion service of possibility of need for massive transfusion).

Result

preparation for transfusion/surgery

Investigations to consider

MRI placenta

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Result
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Should be ordered if placenta accreta spectrum or abruption cannot be reliably excluded on ultrasound.[2][41][54]

MRI is also useful in the assessment of a posterior placenta.[40][41][42]

Result

position of placenta and degree of invasion of the uterus; variable

INR/PTT, fibrinogen, and fibrinogen degradation products

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Result
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Requested if evidence of disseminated intravascular coagulation (DIC) is present (such as petechiae, ecchymosis, gangrene, mental disorientation, hypoxia, hypotension, or gastrointestinal bleeding).

Result

abnormal if DIC is present: elevated INR/PTT and fibrinogen degradation products; decreased fibrinogen

Kleihauer-Betke test

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Result
Test

Should be ordered if mother is Rh negative.[5]

The level of fetal red blood cells aids in determining the need for and amount of Rh immunoglobulin that is required for prophylaxis for Rh disease in subsequent pregnancies.[46]

Result

fetal red blood cells in the maternal circulation; variable

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