Davison J M, Vallotton M B, Lindheimer M D
Br J Obstet Gynaecol. 1981 May;88(5):472-9. doi: 10.1111/j.1471-0528.1981.tb01019.x.
In nine women studied serially before conception and through the first trimester, plasma osmolality (Posm) started to decline with the first missed menstrual period, was significantly decreased by the fifth week of pregnancy and was 10 mosmol/kg lower than preconception values by the tenth week, changing little thereafter. Changes in plasma sodium (and its attendant anion) accounted for the majority of the decrement. In separate studies, urinary concentration and dilution, assessed by water deprivation and loading, studied in nine women during their last trimester and again 10-12 weeks post partum. Basal Posm was 9 mosmol/kg lower in the last trimester than post partum (p less than 0.001) but the results of concentration and dilution tests were similar during and after pregnancy. Basal urinary arginine vasopressin (AVP) excretion was similar during and after pregnancy and water loading suppressed AVP excretion in both pregnant and postpartum women. An unanticipated observation was that lateral recumbency interfered with urinary concentration tests in both pregnant and postpartum women. The results demonstrate that the decrement in Posm during pregnancy is an early event. The data (urinary AVP excretion, its suppression by water loading and normal concentration and dilution despite a lower plasma tonicity) also suggest that human pregnancy is accompanied by a resetting of the threshold for vasopressin secretion to a lower Posm.
在对9名女性进行孕前及孕早期连续研究时发现，血浆渗透压（Posm）在首次停经时开始下降，在妊娠第5周时显著降低，到第10周时比孕前值低10 mosmol/kg，此后变化不大。血浆钠（及其伴随阴离子）的变化占了下降的大部分原因。在另外的研究中，通过禁水和饮水负荷评估的尿浓缩和稀释功能，在9名女性妊娠晚期及产后10 - 12周进行了研究。妊娠晚期的基础Posm比产后低9 mosmol/kg（p小于0.001），但妊娠期间和产后的浓缩和稀释试验结果相似。基础尿精氨酸加压素（AVP）排泄在妊娠期间和产后相似，饮水负荷抑制了孕妇和产后女性的AVP排泄。一个意外的观察结果是，侧卧位会干扰孕妇和产后女性的尿浓缩试验。结果表明，妊娠期间Posm的下降是一个早期事件。这些数据（尿AVP排泄、饮水负荷对其的抑制以及尽管血浆张力较低但浓缩和稀释功能正常）也表明，人类妊娠伴随着血管加压素分泌阈值重置为较低的Posm。
