Physiology of intra-abdominal volume during pregnancy.

A total of 580 pregnant and 50 puerperal women were included in this cross-sectional study to assess the physiological changes that allow women to adapt to a chronic increase in intra-abdominal pressure during pregnancy. The volume of the uterus, intra-abdominal volume (IAV), visceral and subcutaneous fat was calculated. During pregnancy, the IAV increases up to 1.5 times. Changes in IAV until 24 weeks present a linear relationship (5.2%); thereafter, changes become exponential and, at 40 weeks, IAV increases by 61%. This fact is exclusively related to the progressive growth of the foetus and to the increase in uterine size. At term, the IAV reserve is exhausted, becoming equal the anteroposterior and transverse diameters of the abdomen.In conclusion, the adaptive capabilities of IAV related to the foetal growth are limited by the IAV reserve. The reserve capacity of the IAV and tensile properties of the abdominal wall can be estimated by the dynamics of the anteroposterior and transverse abdominal diameters.IMPACT STATEMENT A causal relationship between intra-abdominal hypertension and the development of adverse obstetric and perinatal outcomes has been suggested. Nevertheless, the role of this condition as a leading cause of systemic dysfunction during pregnancy remains unrecognised and underestimated. This study assesses the dynamics of IAV in uncomplicated singleton pregnancies. The study of abdominal pressure indicators such as intra-abdominal volume and compliance will help to a better understand the aetiology, pathophysiology, prognosis and treatment strategies for pregnant women with intra-abdominal hypertension.