An ultrasound study of gestational and postural changes in the deep venous system of the leg in pregnancy.

OBJECTIVE: To investigate gestational and postural changes in diameter and blood flow in the proximal deep leg veins during pregnancy.

DESIGN: A longitudinal, prospective observational study.

SETTING: The ultrasound department of a teaching maternity hospital.

POPULATION: Twenty-four healthy women with uncomplicated singleton pregnancies.

METHODS: Real-time and duplex Doppler ultrasound assessments of the vessel diameter, flow velocity and respiratory flow fluctuation in the proximal deep leg veins of women serially measured from the first trimester of pregnancy to six weeks postnatally.

MAIN OUTCOME MEASURES: The effects of increasing gestation and the adoption of the left lateral position on the above parameters.

RESULTS: An increase in vessel diameter and a fall in flow velocity with increasing gestation was observed. However, no change in venous flow variation was observed. Delivery had reverse effects. Flow velocity was slower in the left than right legs, but on adoption of the left lateral position an increase in flow velocity and venous flow variation was observed in both legs during pregnancy.

CONCLUSIONS: These data are consistent with the observed increase in incidence and pattern of deep venous thrombosis in pregnancy and may aid interpretation of duplex Doppler ultrasound examinations for deep venous thrombosis in pregnancy. Postural changes should be part of this evaluation. The gravid uterus may not be the sole cause for postural changes in deep venous flow velocity.