If there is a major problem with either the production of liquor (amniotic fluid), or the outflow from the bladder to the amniotic cavity then there will be little or no liquor around the fetus. This has devastating consequences for the development of the fetal lungs. If there is no liquor production the normal development of the fetal lungs cannot occur.

When there is little or no liquor around a fetus the quality of the ultrasound images obtained is often poor. If the bladder is seen it is most likely that the lack of liquor is due to either rupture of membranes or severe placental failure, both of which can give a similar pattern of reduced liquor volume. In some cases, it may be difficult to be certain whether there is any renal tissue present or not. The bladder is more easily seen on ultrasound than the kidneys.

If there is no liquor production the baby when born will be unable to get oxygen into its blood stream despite normal attempts to resuscitate with 100% oxygen and positive pressure ventilation. This observation was first made with renal agenesis (Potter's syndrome), where there is no renal development and therefore a very small liquor volume from approximately 16 weeks gestation. In less severe cases the prediction of outcome is more difficult, but certain general principles apply. If there is good liquor volume up until 24 weeks gestation, pulmonary hypoplasia leading the neonatal death is uncommon. Even before this gestation if there are more than two pools of liquor which are more than 2 cm deep then the chances of severe lung problems is small.

After 24 weeks gestation is much less likely to be due to renal anomalies, and the other causes, namely rupture of membranes and placental failure need to be considered. Although occasionally a cause of major fetal problems, these diagnoses will usually have a good outcome.