Blood flow to the scarred gravid uterus at 22-24 weeks of gestation

To compare uterine artery volume blood flow (Q(uta)), vascular resistance (R(uta)), pulsatility index (Uta PI), and the fraction of maternal cardiac output (CO) distributed to the uteroplacental circulation in pregnant women with and without a previous caesarean section.

Cross-sectional observational study.

University hospital in Norway.

Thirty-two pregnant women with previous caesarean section and 32 matched controls.

Ultrasonography was used to measure uterine artery diameter and blood flow velocity between 22(+0) and 23(+6) weeks of gestation. Impedance cardiography was used to assess maternal haemodynamics.

Q(uta), R(uta), Uta PI, and the fraction of maternal CO distributed to the uteroplacental circulation.

The mean Q(uta) was 356.26 ± 213.72 ml/minute in cases and 456.41 ± 209.70 ml/minute in controls (P = 0.038). R(uta) was significantly (P = 0.026) higher among cases compared with controls (0.32 ± 0.20 versus 0.22 ± 0.14 mmHg/ml/minute), but the Uta PI did not differ between the groups (0.93 ± 0.23 versus 0.92 ± 0.47; P = 0.929). The fraction of maternal CO distributed to the uteroplacental circulation was 5.75 ± 3.68% in cases and 8.45 ± 5.02% in controls (P = 0.014).

Uterine artery volume blood flow and the fraction of maternal cardiac output distributed to the uteroplacental circulation are lower, and uterine vascular resistance (but not Uta PI) is higher, in women with previous caesarean section compared with the control group.