Fetal Factors Influencing the Volume and Composition of Liquor Amnii*

Summary At 18 weeks gestation the liquor volume increases by 10–13 ml. per day. The fetus swallows 4–11 ml. per day and may void 7–17 ml. per day, while fetal renal function matures with increasing age. Some anencephalic fetuses can swallow considerable volumes of liquor, but the presence or absence of swallowing plays little part in the aetiology of polyhydramnios in this condition. A review of clinical evidence, together with these experimental findings, throws considerable doubt on present theories that fetal swallowing and voiding are important factors in controlling the liquor volume.