Abdominal pregnancy: a perfusion confusion?

BACKGROUND

The uteroplacental blood supply is usually portrayed as a 'series' circuit. Differences seen in the uterine artery (UA) waveform in pregnancies destined to develop pre-eclampsia are often attributed to back pressure effects from the downstream flow through the spiral arteries of the placental bed.

CASE: A third trimester abdominal pregnancy was successfully delivered by laparotomy at 30 weeks gestation. The UA waveforms of were recorded at 27 weeks. Both were 'normal' for the gestation, despite limited blood supply from the right uterine and the left not supplying the placenta at all.

CONCLUSION

In the absence of pre-eclampsia, UAs can convert to a 'low resistance' waveform even when not directly connected to the placental bed. This case report adds to the evidence against the 'cause and effect' mechanism often used to explain the correlation between trophoblastic invasion and the UA waveform. Both may independently develop in response to a common underlying mechanism.