The objective is to retrospectively gather peri-operative data on neonatal outcomes, primarily neonatal acid-base status, based on umbilical cord gas analysis, for the 23 months preceding and 23 months following the conduct of the "tilt versus supine study". The investigators hypothesize that there will be no difference in mean neonatal umbilical artery base excess in neonates delivered by cesarean section during the period before and after conduct of the study, for elective, urgent and emergent deliveries.

For decades, obstetric anesthesia dogma for term women undergoing cesarean delivery (CD) includes maintenance of left lateral tilt for uterine displacement until delivery, based on the premise that the supine position will result in aortocaval compression (ACC), maternal hypotension and fetal compromise. More recent evidence suggests that even in 15 degrees of left tilt, there is minimal relief of aortocaval compression. Furthermore, there is evidence that most practitioners never achieve 15 degrees of tilt anyway.

Between January 2015 and January 2016, the investigators conducted a randomized clinical trial at NewYork Presbyterian/The Allen Hospital in which healthy women undergoing elective CD were randomized (non-blinded) to supine horizontal (SUPINE, N=50) or 15° left tilt of the surgical table (TILT, N= 50) following spinal anesthesia (hyperbaric bupivacaine 12 mg, fentanyl 15 μg, preservative-free morphine 150 μg). Lactated Ringer's 10ml/kg and a phenylephrine (PE) infusion titrated to 100% baseline systolic blood pressure (SBP) were initiated with intrathecal injection. The primary outcome was umbilical artery base excess (UA-BE). There were no differences in UA-BE or pH between groups. The mean UA-BE (± SD) was -0.5 mmol/L (± 1.6) in the SUPINE group (n=50) versus -0.6 mmol/L (± 1.5) in the TILT group (n=47) (p= 0.64). The conclusion was that maternal supine position during elective CD with spinal anesthesia in healthy term women does not impair neonatal acid-base status compared to 15° left tilt, when maternal SBP is maintained with a coload and PE infusion. The investigators understood that the findings may not be generalized to emergency situations or non-reassuring fetal status.

Since the end of the study, discussion of the findings with colleagues at Departmental grand rounds and national conferences, and a publication in the journal Anesthesiology, practitioners have reported feeling more comfortable with maternal supine position during cesarean delivery, as long as maternal SBP is kept at or near to baseline with crystalloid infusion and a PE infusion. It is routine practice at CUMC to use a prophylactic PE infusion for maintenance of maternal SBP close to or at baseline. It is also routine at CUMC to send samples of umbilical arterial and venous blood for analysis. Much of the dosing for neuraxial anesthesia (spinal, combined spinal epidural anesthesia and epidural doses) are standardized at CUMC. The investigators believe that since there has been a noticeable practice shift with practitioners anecdotally reporting that they have discontinued the routine use of left maternal tilt intraoperatively, the investigators will be able to collect useful data on cases which had not been studied - these include cases with preeclampsia, morbid obesity and emergencies.

Inclusion Criteria:

• Women who delivered between February 2013 and December 2014, and between February 2016 and December 2017

Exclusion Criteria:

• none

Retrospective cohorts of women who delivered between February 2013 and December 2014, and between February 2016 and December 2017

Will not share patient identifiable data with other researchers.