The effects of myometrial activity on fetal thoracic dimensions and uterine blood flow during late gestation in the sheep.
We wished to investigate mechanisms by which non-labour contractions of the uterus influence fetal sleep states and respiratory activity during late pregnancy. The relationship between the dimensions of the fetal chest and uterine contractions was examined in 5 pregnant sheep. The dorso-ventral dimension at the level of the xiphisternum (3 fetuses) decreased, on average by 4.4-9.4% while increases of 16.6-18.7% were seen in the transverse dimension (4 fetuses). Blood flow in a middle uterine artery was monitored using a Doppler technique in 5 pregnant sheep. Non-labour uterine contractions were accompanied by mean reductions of 6.5-12.7% in blood flow. Postural adjustments by the ewe also influenced uterine blood flow. A mean increase in blood flow of 5.9-12.0% followed a change from standing to lying; standing caused a mean reduction of 5.9-11.8%. We conclude that the influence of uterine contractions on the fetus is likely to be complex, involving distortion of the body and alterations in utero-placental haemodynamics.
D000818:Animals; D005260:Female; D005333:Fetus / Q000502:physiology*; D005865:Gestational Age; D011247:Pregnancy; D012039:Regional Blood Flow; D012119:Respiration; D012756:Sheep / Q000196:embryology / Q000502:physiology*; D012890:Sleep / Q000502:physiology; D013909:Thorax / Q000033:anatomy & histology / Q000196:embryology*; D014590:Uterine Contraction; D014599:Uterus / Q000098:blood supply*