S232 SMFM Abstracts

556 IS A LECITHIN/SPHYNGOMYELIN (L/S) RATIO ->3 THE BEST PREDIC- T O R OF PRESENCE OF PHOSPHATIDYLGLYCEROL (PG) IN DIABETIC WOMEN? ALESSANDRO GHIDINI l, CATHERINE SPONG 2, J O H N PEZ- ZULLO1; 1Georgetown University, Obstetrics and Gynecology, Washington, DC; 2National Institutes of Health, hnt444

OBJECTIVE: Diabetes is associated with delayed onset of fetal l ung maturity. Documentat ion of an L /S ratio ->3 or presence of PG in the amniotic fluid is commonly considered p roof of fetal lung maturity. An predictors of fetal lung maturity. However, no study to date has assessed whether an L / S ratio of->3 is equivalent to presence of PG, or whether some other value of L / S better corresponds to the presence of PG.

STUDY DESIGN: A database of clear amniotic fluid specimens obtained by amniocentesis in diabetic women with s ingleton fetuses was accessed. Receiver opera t ing characterist ic (ROC) curve analysis was const ructed of different L / S ratios to identify the opt imal th reshold for predic t ion of presence of PG. Sensitivity was defined as the rate of L / S ratios above a certain threshold a m o n g cases with present PG. False positive rate was that of L / S ratios above a threshold which was present among cases with absent PG.

RESULTS: As anticipated, there was a significant relationship between L /S ratios a n d presence of PG (area u n d e r the curve = 0.955, P < .0001). Surprisingly, a L / S of ->2.5 h a d similar false positive rate (0%) bu t bet ter sensitivity (90% vs 59%) than an L / S ratio of ->3 in the predict ion of present PG.

CONCLUSION: In diabetic p r e g n a n t patients, presence of PG in the amniotic fluid more closely corresponds to an L / S ratio of->2.5 than ---3.

558

December 2001 A m J Obstet Gynecol

PROLONG PRENATAL HYPERNATREMIA ALTERS ELECTROLYrES HOME- OSTASIS: EVIDENCE OF IMPRINTING OF OSMOREGUI~TORY PATHWAY SHENGBIAO WANG 1, JIEXIONG CHEN 1, NATHASH KALLICHANDA l, MICHAEL ROSS 1, 1University of California, Los Angeles, Harbor-UCLA Medical Center, Torrance, CA

OBJECTIVE: Water a n d electrolytes homeostasis are critical du r ing neonatal per iod and regulated by Arginine vasopressin (AVP).Our previous studies suggest that p ro longed in utero plasma hyperosmolali ty alters AVP synthesis and secret ion in newborn lambs. The p resen t studies were to de te rmine the effect of p r o l o n g e d materna l hyperna t remia on water electrolytes homeostasis in lamb.

STUDY DESIGN: P regnan t ewes at 119 _+ 3 days gestat ion were water restricted to achieve and maintain hypernatremia (6-8 m E q / L above baseline level) unti l no rma l term delivery. Newborns were provided ad l ibitum maternal nursing, and allowed for ad libitum food and water after weaning. At age of 2 months, study (n = 4) and age matched control (without prenatal dehydra t ion) (n = 3) lambs were surgically p repa red with vascular catheterizations. At day 7 post surgery, following b lood withdrawal for measurement of baseline plasma osmolality, Na+, K+ and CI-, lamb were given introvenous infusion of hypertonic saline to achieve and maintain the plasma Na+ at 10% above baseline level for a total of four h o u r . Five days after this acute hypernatremia , plasma osmolality and electrolytes were determined. Data were analyzed by paired and unpaired T test and presented as mean -+ SEM.

RESULTS: Baseline plasma Na÷ in prenatally dehydrated lambs is h igher that the controls (146.0 _+ 0.7 vs 143.1 _+ 0.4 mEq/L, P < .05). There are no statistically difference in baseline plasma osmolality, K+ or C1- between study and control groups. Five days after acute hypernatremia , plasma Na+ level (143.7 _+ 0.6mEq/L) in control lambs were similar to the baseline (143.1 _+ 0.4). To the contrary, in prenatal ly dehydra ted lambs, the plasma Na+ were significantly lower than the baseline (143.5 +- 0.8 vs 146.0 _+ 0.7 mEq/L, P < .05).

CONCLUSION: Chronic prena ta l hyperna t remia increases baseline plasma Na+ level and alters osmotic response to acute hyperna t remia two months after birth. These results suggest the imprint ing of osmoregnlat ion in sheep.

557 EXPRESSION AND LOCALIZATION OF AQUAPORIN-I IN HUMAN FETAL MEMBRANES STEPHANIE MANN l, EMILY RICKE 2, ROBERT TAY- LOR 1, BAXOUE YANGt, ALAN VERKMAN1; 1University of California, San Francisco, Obstetrics or Gynecology, San Francisco, CA; 2UCSF, Obstetrics and Gynecology, San Francisco, CA

OBJECTIVE: Aquaporins (AQPs) are a family of water selective channels that facilitate water movement across cell membranes; specifically, aquaporin-1 (AQP-1) is impor tant in osmotic water movement across membranes. During pregnancy, a significant osmotic gradient exists across the placenta between the amniotic cavity and fetal circulation such that approximately 400 ml of water per day move across the membranes directly overlying the p lacenta (chorionic plate). The exact mechanisms underlying the movement of water across this pathway have yet to be elucidated. O u r goal was to 1) determine if AQP-1 mRNA a n d / o r prote in are expressed in the h u m a n chorioamniot ic membrane and 2) determine the precise site(s) of AQP-1 protein expression.

STUDY DESIGN: Placentas were collected f rom women with intact membranes who were not in labor and underwent elective cesarean sections at t e rm (37-40 wks). The chor ionic plate membranes and the free f loat ing reflected membranes were sampled. RNA and protein were isolated from the amnion and chorion. RT-PCR and Western analysis were used to determine expression of mRNA and protein; immunohistochemistry was used to localize AQP-1.

RESULTS: AQP-1 mRNA was found in amnion and chor ion f rom both membrane locations. Western analysis also yielded positive results for amnion a n d chor ion f rom both locations. Immunohi s tochemica l s ta ining showed AQP-1 to be present only on the apical aspect of the chorionic plate amnion epithelium.

CONCLUSION: AQP-1 is present in h u m a n fetal membranes. AQP-I may play a role in water movement f rom the amniotic cavity across the placenta into the fetal circulation. Further studies are needed to clarify our unders tanding of the role of fetal membrane AQPs in amniotic fluid homeostasis.

559 MULTIPLE GESTATION IS ASSOCIATED WITH H I G H LEVELS OF ADRENOMEDUIXJN IN MATERNAL CIRCULATION GABRIELLE URBAN t, MICHAEL PAIDAS 1, E MARINONI 2, R DI IORIO 2, ANDREI REBARBER 1, JEANINE MATURD, SANA KHAN 3, CHARLES LOCKWOOD1; ]New York University, Obstetrics and Gynecology, New York, NY; 2University of Rome, Rome; 3New York University, Obstetrics and Gynecology, Staten Island, NY

OBJECTIVE: Adrenomedull in (AM) is a vasoactive peptide p roduced by the placenta that participates in the hemodynamic adapta t ion of maternal vascular system to p regnancy a n d regulates fe toplacental circulat ion. We assessed AM longitudinally in the maternal circulation in multiple gestation pregnancies.

STUDY DESIGN: Thirty women with uncomplicated multiple pregnancies and 23 women with s ingleton pregnancies were studied. Maternal p lasma samples were collected in the firsl (6-12 weeks), second (13-25 weeks), and third trimester of pregnancy (26-40 weeks). AM was assayed by means of a specific RIA kit (Phoenix Pharmaceuticals, Mountain View, CA).

RESULTS: In the second and third trimester maternal AM concentrat ions were significantly higher in multiple than in singleton pregnancies (40.7 -+ 2.2 and 84.7 -+ 9.9 p g / m L vs 33.4 _+ 2.2 and 57.1 _+ 4.9 p g / m L respectively, P< .05). In the third trimester, mean AM levels were h igher in triplet (88.6 _+ 15.7 p g / m L ) than in twin pregnanc ies (77.9 -+ 12.6 p g / m L ) a l though this difference did not reach statistical significance. AM concentrat ion correlated with gestational age in multiple gestation (r = 0.677, P < .01), as well as in singleton gestation (r = 0.721, P< .01). No correlation was found between third trimester AM levels, placental, and birthweight in both groups.

CONCLUSION: Multiple gestation is associated with a modification of materna l and placental endocr ine axis that leads to dramat ic changes in maternal hemodynamics ensur ing an adequate transfer of nutr ients to the fetuses. Increased levels of circulating AM in multiple gestation may derive from an enhanced release by maternal endothelial cells and participate in the systemic vascular modificat ions that occur du r ing the second a n d th i rd trimester of pregnancy. In addition, since AM acts as a paracr ine /au tocr ine hormone , increased AM may also derive f rom a greater number of placental t rophoblast cells noted in multiple gestation.