Behavioural state dependency of renal artery and descending aorta velocimetry and micturition in the normal term fetus.

OBJECTIVE

To examine the behavioural state dependency of renal artery and descending aorta pulsatility index and hourly fetal urinary production rate (HFUPR) in the normal term fetus.

DESIGN

An observational study.

SUBJECTS

Twenty-three healthy women with a normal singleton pregnancy between 36 and 40 weeks gestation.

MAIN OUTCOME MEASURES

Renal artery and descending aorta pulsatility indices were established using pulsed Doppler ultrasound. HFUPR (ml) was estimated using real-time ultrasound. Fetal behavioural states 1F (quiet sleep) and 2F (active sleep) were determined from combined recordings of fetal heart rate, eye movements and body movements.

RESULTS

An inverse correlation between pulsatility index and fetal heart pattern was established for both the renal artery (r = 0.60; SD = 0.22; P = 0.0001) and the descending aorta (r = 0.73; SD = 0.16; P = 0.0001). The difference in mean pulsatility index between states 1F and 2F adjusted for fetal heart pattern was 0.09 (SD 0.23) for the renal artery (P = 0.02) and 0.26 (SD 0.19) for the descending aorta (P = 0.0001). Mean HFUPR was significantly higher (44.8%, P = 0.01) in state 1F (96 ml) compared with state 2F (54 ml). During the urinary filling phase, a poor correlation existed between renal artery pulsatility index and HFUPR (r = 0.04) and between descending aorta pulsatility index and HFUPR (r = 0.01).

CONCLUSIONS

In the normal term fetus renal artery and descending aorta pulsatility indices are reduced during fetal behavioural state 2F, suggesting reduced downstream impedance at the fetal trunk and in particular at renal level. This behavioural state is, however, also associated with reduced micturition. No correlation exists between renal artery and descending aorta pulsatility indices and fetal urinary output.