1. Serial pulmonary haemodynamic investigations were performed in 13 women before conception, at monthly intervals throughout pregnancy, and then at 6 months after delivery.

2. Mean pulmonary artery pressure was calculated from pulsed Doppler pulmonary velocities. Pulmonary flow was measured by Doppler and cross-sectional echocardiography. These two measurements were used to calculate pulmonary vascular resistance.

3. Mean non-pregnant pulmonary artery pressure was 13.8 mmHg and no significant change was demonstrated during pregnancy.

4. Pulmonary flow increased from 4.88 to 7.19 litres/min during pregnancy.

5. Pulmonary vascular resistance decreased from 2.85 resistance units before pregnancy to 2.17 resistance units at 8 weeks gestation. Thereafter there was no further significant change, values returning to pre-pregnant levels by 6 months after delivery.

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