Effect of Maternal Hydration on Amniotic Fluid Volume Everett F. Magann, MD, Dorota A. Doherty, PhD, Suneet P. Chauhan, MD, Scott P. Barrilleaux, MD, Lisa A. Verity, MD, and James N. Martin, Jr, MD OBJECTIVE: To estimate the effects of maternal intravenous hydration on amniotic fluid volume in normal pregnan- cies. METHODS: Women undergoing an amniocentesis for the evaluation of fetal lung maturity before an elective cesar- ean delivery were eligible to participate. An amniotic fluid index (AFI) was obtained before the amniocentesis, and at the time of the amniocentesis the amniotic fluid (AF) vol- ume was determined by diazo-dye reaction with subse- quent spectrophotometric analysis of AF samples. If the AF sample drawn for fetal maturity studies was mature, the patient was hydrated with 1000 mL of balanced salt solu- tion 30 minutes before her cesarean delivery. Amniotic fluid volume was subsequently estimated after the hydra- tion by a repeat AFI. Amniotic fluid volume was directly measured at cesarean delivery and compared with the dye-determined volume. The pre- and posthydration AFI were also compared. RESULTS: A total of 17 women participated in the study between January 2001 and June 2001. Statistically signifi- cant increases in the AF volume and AFI were found. The prehydration median AF volume was 450 mL (range 250 – 953), and the median increase in AF volume was 188 mL (95% confidence interval [CI] 60, 254 mL; P < .001). Me- dian AFI was 8.6 (range 5.8 –17.8) with a median change in AFI of 1.7 cm (95% CI 1.1, 3.0; P < .001). CONCLUSION: Maternal intravenous hydration appears to increase both the actual and ultrasound-estimated AF vol- umes in normal third-trimester pregnancies. (Obstet Gy- necol 2003;101:1261–5. © 2003 by The American College of Obstetricians and Gynecologists.) Amniotic fluid (AF) volume assessment is an important component of antenatal testing of the fetus at risk for an adverse pregnancy outcome. Both the modified biophys- ical profile (nonstress test [NST] and amniotic fluid index [AFI]) 1 and the standard biophysical profile (movement, tone, breathing, NST, and presence of a 2  1 cm pocket of fluid) 2 include an ultrasound estimation of the ade- quacy of AF volume as an important component of fetal testing. Pregnant patients with a low ultrasound estimation of AF volume obtained at term (37 weeks) are sometimes admitted to the hospital for induction of labor with intent to deliver. In preterm pregnancies (less than 37 weeks) with a low estimated AF volume by AFI, patients fre- quently undergo additional testing, hydration, and even administration of corticosteroids to enhance fetal lung maturity with subsequent early delivery. Oral hydration with hypotonic fluids has been reported to increase the AF volume as measured by the AFI 3–9 or measured by an increase in fetal urine production. 10,11 Intravenous (IV) hydration with hypotonic but not isotonic fluid is reported as increasing the AFI. 12 Other reports, how- ever, have described an increase in the AFI with IV hydration using an isotonic solution. 13–15 A PubMed search was undertaken to determine whether dye-dilution techniques followed by IV hydra- tion and subsequent direct measurement of the AF had been undertaken. The terms “dye dilution, hydration” and “dye dilution, hydration, amniotic” yielded no arti- cles. This investigation was undertaken to determine, by using dye-determined and directly measured volumes, the influence of IV hydration with an isotonic solution on AF volume. MATERIALS AND METHODS Women with singleton pregnancies undergoing an am- niocentesis for the assessment of fetal lung maturity before a planned cesarean delivery were eligible to par- ticipate in this investigation. Exclusion criteria were women who ruptured their membranes after the amnio- centesis but before the planned cesarean delivery, women whose fetal maturity studies were immature, From the Department of Obstetrics and Gynecology, University of Western Aus- tralia, Perth, Australia; Department of Obstetrics and Gynecology, Spartanburg Regional Hospital Center, Spartanburg, South Carolina; and Department of Obstetrics and Gynecology, The University of Mississippi Medical Center, Jackson, Mississippi. Supported in part by the Vicksburg Hospital Medical Foundation, Vicksburg, Mississippi. 1261 VOL. 101, NO. 6, JUNE 2003 0029-7844/03/$30.00 © 2003 by The American College of Obstetricians and Gynecologists. Published by Elsevier. doi:10.1016/S0029-7844(03)00344-2