Relation between oligohydramnios and spinal flexion in the human fetus

Oligohydramnios, a severe reduction in the volume of amniotic fluid, is associated with fetal lung hypoplasia but underlying processes are unclear. Studies in sheep suggest that oligohydramnios may lead to lung hypoplasia by causing increased flexion of the fetal spine, but this has not been demonstrated in the human, which has a different uterine anatomy.

Our aims were to quantify spinal flexion in the human fetus and to determine the relationship between oligohydramnios and the degree of spinal flexion.

In 35 pregnancies, we used ultrasonography to assess amniotic fluid volume and to image the fetal spine so as to provide an index of mean spinal radius between the upper thoracic and lumbar spine. In 17 pregnancies with evidence of oligohydramnios resulting from premature rupture of membranes (mean +/- SEM gestation 28.8 +/-1.4 weeks), the mean radius of fetal spinal curvature between the upper thorax and sacrum was compared with values from 18 control fetuses with normal amounts of amniotic fluid (at 28.9 +/- 1.6 weeks).

In each fetus, the spine could be imaged and the mean radius of curvature calculated. Oligohydramnios was associated with a significantly increased degree of fetal spinal flexion compared to controls.

In human pregnancy, oligohydramnios is associated with increased flexion of the fetal spine, which is likely due to reduced uterine volume. This could contribute to the development of fetal lung hypoplasia, fetal immobility and other fetal anomalies.