Maternal dehydration-rehydration: fetal plasma and urinary responses

Abstract

Pregnant women may be exposed to exercise, thermal, or gastrointestinal (hyperemesis) water loss, all of which commonly induce a greater than 10 mosmol increase in plasma osmolality. Although fetal osmolality is dependent on maternal osmolality, the impact of maternal dehydration and subsequent maternal rehydration on the fetus has not been explored. Five pregnant ewes with singleton fetuses (136 +/- 1 day) were water deprived for 36 h resulting in a significant increase in plasma osmolality (298 +/- 3.4 to 313 +/- 5.0 mosmol). In response to maternal dehydration, fetal plasma osmolality (297.0 +/- 4.1 to 309.3 +/- 4.1 mosmol), arginine vasopressin (AVP) levels (1.5 +/- 0.2 to 7.9 +/- 1.0 pg/ml), hematocrit (35.1 to 38.6%), and urine osmolality (161.3 +/- 10.7 to 348.9 +/- 21.9 mosmol) significantly increased. Subsequently, ewes were rehydrated over 4 h with intravenously infused 0.45% saline (20 ml.kg-1.h-1). In response to maternal rehydration, maternal and fetal plasma osmolality decreased to basal values (298.9 +/- 3.2 and 300.1 +/- 3.8 mosmol, respectively) and fetal glomerular filtration rate (1.72 +/- 0.30 to 3.08 +/- 0.66 ml/min) and urine volume significantly increased (0.33 +/- 0.02 to 0.71 +/- 0.13 ml/min). However, fetal hematocrit (37.4%), plasma AVP (3.1 +/- 0.9 pg/ml), and urine osmolality (255.4 +/- 28.8 mosmol) did not return to basal levels during the observation period. These results demonstrate fetal hyperosmolality, blood volume contraction, AVP secretion, and altered urine production in response to maternal dehydration. Despite maternal rehydration and normalization of maternal and fetal plasma osmolality, fetal endocrine and fluid responses are prolonged.(ABSTRACT TRUNCATED AT 250 WORDS)

Fetal and maternal fluid balance in sheep during hyperthermia with and without water deprivation

“…In response to maternal water deprivation alone, the alterations seen by us in maternal and fetal plasma and fluid compositions, and in the production rates of maternal and fetal urine and lung liquid, were similar to those shown previously (Bell, Congiu, Hardy & Wintour, 1984;Stevens & Lumbers, 1985;Ross et al 1988). …”

Fetal Rehydration Via Intraamniotic Fluid: Contribution of Fetal Swallowing

“…In a previous study, maternal i.v. der anaerobic conditions, which reduce plasma carbon diox-rehydration resulted in decreased fetal plasma osmolality but a ide loss, indicate actual plasma osmolality gradients of 2 to 3 continued elevation of plasma AVP (5). As dehydration-induced mosmol/kg (10).…”

“…Maternal water restriction significantly alters maternal and fetal fluid dynamics (3)(4)(5)(6). In the pregnant ewe, dehydrationinduced maternal plasma hyperosmolality and hypernatremia are associated with elevated levels of plasma AVP.…”

“…Fetal plasma osmolality and sodium concentrations parallel maternal values, whereas increases in fetal plasma AVP are gestation-dependent (3). The fetus also may exhibit a relative decrease in plasma volume, glomerular filtration rate, and urine production (3)(4)(5). Urinary hyperosmolality, mediated in part by increased plasma AVP, contributes to increased amniotic fluid osmolality (1-3), whereas reduced urine production likely contributes to decreased amniotic fluid volume during dehydration (6).…”

“…Urinary hyperosmolality, mediated in part by increased plasma AVP, contributes to increased amniotic fluid osmolality (1-3), whereas reduced urine production likely contributes to decreased amniotic fluid volume during dehydration (6). Intravenous rehydration of the maternal ewe results in the reversal of maternal plasma composition changes and a gradual equilibration of fetal plasma composition, via transplacental fluid flow (5). In view of the potential for fluid exchange between the amniotic cavity and the fetus, we sought to determine if the dehydrated ovine fetus was able to use hypotonic amniotic fluid for rehydration.…”