715: Efficiency of nitrous oxide in external cephalic version on succes rate: a randomized controlled trial

Poster Session IV concentration correlating with Cmax (ACM: 30 mg/ml; ACM-S: 10 mg/ml; ACM-G: 25 mg/ml) and Css in normal clinical use (ACM: 10 mg/ml; ACM-S: 5 mg/ml; ACM-G: 12.5 mg/ml). Antipyrine (AP) 100 mg/mL was added as internal control. ACM, ACM-S, ACM-G and AP concentrations were determined with HPLC. Samples were taken at 0, 3, 6, 10, 15, 20, 30 min then every 15 min until 150 min followed by every 30 min until 210 (ACM) or 360 min (ACM-S and ACM-G). FM and MF ratios were normalized for AP for each time-point. RESULTS: FM and MF-transfer ratios, concentrations, number of perfusions and placental transfer are shown in table 1. For MFtransfer of ACM an equilibrium between the maternal and fetal concentrations is reached within 180 min. Extrapolation of data till 360 min reveals equilibrium will be reached at 7.5 h (ACM-S) and 9.5 h (ACM-G). For FM-transfer extrapolation of data till 210 min (ACM) and 360 min (ACM-S and ACM-G) reveals equilibrium will be reached for ACM after 270 min, ACM-S 36 h and ACM-G 44 h. CONCLUSION: This study shows that ACM rapidly crosses the placental barrier via passive diffusion for both MF and FM transplacental transfer. ACM-S and ACM-G, larger and more hydrophilic molecules, cross the placenta but in a significantly lower rate. For ACM-S and ACM-G FM transport is slower then MF transport.

ajog.org air. The primary endpoint was ECV success rate. Secondary endpoints were degree of pain assessed by Visual Analog Scale (VAS), and adverse event rate. RESULTS: One hundred and fifty women were included (nitrous oxide group: n¼74 and medical air: n¼76). Inhaled nitrous oxide was not associated with a higher rate of success of ECV compared to medical air (24.3% vs. 19.7%, p¼0.51). In multiparous women (n¼34 in each group), there was significantly associated with a higher rate of success of ECV in the nitrous oxide group (47.1% vs. 23.5%, p¼0.048). After adjustment for confounding factors (parity and transverse position) in the multivariate logistic regression analysis, inhaled nitrous oxide was not associated with a higher rate of success of ECV compared to medical air (adjusted odds ratio [OR] 0.78, 95% confidence index [CI] 0.26-2.34). Multiparity (aOR 4.57, 95%CI 1.47-14.20) and polyhydramnios (aOR 12.14, 95%CI 1.37107.53) were significantly associated with success of ECV. The median level of pain was not statistically different in women with inhaled nitrous oxide compared to medical air (VAS median¼5.9; range, 0-10, vs. VAS median¼5.6; range, 0-10; p¼0.35). Side effects rate related to ECV or inhaled nitrous oxide were not significantly different in both groups. However, an important proportion of patients (86.7%) expressed satisfaction with the procedure and 94% would recommend inhaled nitrous oxide for ECV. CONCLUSION: The use of inhaled nitrous oxide improved the success rate of ECV in multiparous women, but did not decrease external cephalic version-related pain. It was well accepted by women, appeared to be safe both for mother and child, and should be proposed systematically for ECV.

716 Predictors of postpartum hemorrhage following cesarean delivery: a model for calculating risk of transfusion Jaclyn Phillips, Richard Amdur, Aayushi Sardana, Homa Ahmadzia George Washington University, Washington, DC

OBJECTIVE: There has been an appreciable rise in the severity of

715 Efficiency of nitrous oxide in external cephalic version on succes rate: a randomized controlled trial Vincent DOCHEZ1, Julie ESBELIN1, Guillaume DUCARME2, Christelle VOLTEAU1, Norbert WINER1 1 University Hospital of Nantes, Nantes, France, 2Hospital Center of La Roche sur Yon, La Roche sur Yon, France

OBJECTIVE: To analyze the effect of using inhaled nitrous oxide (vs. medical air) for analgesia on the success rate of external cephalic version (ECV). STUDY DESIGN: We conducted a prospective, randomized, open label, controlled, single-center clinical trial at University Nantes Hospital, France. Patients with singleton pregnancies in breech presentation at term that were referred for ECV were assigned according to a balanced (1:1) restricted randomization scheme to inhaled nitrous oxide in a 50:50 mix with oxygen during the procedure or medical

postpartum hemorrhage (PPH) requiring more transfusions in the US. Our objective is to better define patients at greatest risk for severe PPH in order to identify cases for early intervention and monitoring. STUDY DESIGN: Using the MFMU Network’s Cesarean Registry, we identified cases of PPH defined as 1) non-severe (nsPPH): requiring <4 units pRBCs or 2) severe (sPPH): requiring 4 units pRBCs or ICU admission. We used a reference group of no transfusion (no txf). We compared prevalence and severity of hemorrhage associated with maternal, fetal, and socioeconomic risk factors. Multivariate logistic regression models were used to identify predictors that were independently associated with either 1) nsPPH vs no txf, 2) sPHH vs no txf, and 3) any hemorrhage vs no txf. A risk calculator was developed for predicting the need for blood transfusion. RESULTS: We included 13,462 women, with 126 cases of nsPPH (0.9%) and 46 cases of sPPH (0.3%). Hispanic women had an adjusted odds of having both nsPPH and sPPH over twice as high as African Americans. For Asians the adjusted odds ratio is over four times higher, but only for nsPPH. Predictors specific for nsPPH and sPPH are presented in Table 1. For patients with nsPPH, increasing BMI demonstrated a protective effect while with sPPH increasing BMI was a predictor for hemorrhage. Hematocrit and hemoglobin both had a protective effect for transfusion. Using the predictors associated with all hemorrhage, a risk calculator was created to

S418 American Journal of Obstetrics & Gynecology Supplement to JANUARY 2017