Objective: To evaluate the relation between fetal oxygen pressure (PO2), carbon dioxide pressure (PCO2), pH, and 19 fetomaternal Doppler indices that reflect the circulatory changes in growth-retarded fetuses.
Methods: In a cross-sectional study of 32 severely growth-retarded fetuses, the uteroplacental vessels, umbilical artery, middle cerebral artery, common carotid artery, thoracic aorta, abdominal aorta, and umbilical vein were assessed by Doppler ultrasound before funipuncture and measurement of umbilical venous PO2, PCO2, and pH.
Results: Compared to expected values, Doppler measurements from the middle cerebral and common carotid arteries were both decreased ("brain-sparing effect"), whereas thoracic and abdominal aortic Doppler indices were increased in association with increased uteroplacental and/or umbilical impedance. Carbon dioxide pressure and pH both correlated significantly with Doppler indices from the thoracic aorta, abdominal aorta, and common carotid artery. The middle cerebral and common carotid arteries were both significantly related to PO2 and PCO2.
Conclusions: This investigation demonstrates circulatory redistribution in human fetal growth retardation and postulates that compensatory redistribution is regulated by more than one mechanism. Hypercapnia, acting alone or through acidemia, plays a role in the control of carotid and aortic vascular responses, whereas hypoxemia, alone or with hypercapnia and probably through local effects, is responsible for the cerebral vascular responses.