. Author manuscript; available in PMC: 2011 Aug 1.

Published in final edited form as: Pediatrics. 2010 Jul 19;126(2):222–231. doi: 10.1542/peds.2010-0456

TABLE 2.

Relative risk of death in the first 7 days among infants 501–1250 grams birth weight by timing of birth

Timing of birth	N	Death in 7 days	Adjusted RR (95% CI)^a	P- value^a

Birth hour
Late night	3128	427 (14%)	1.07 (0.96–1.18)	0.4
Early night	3578	405 (11%)	1.01 (0.90–1.13)
Day	4431	452 (10%)	1.0

Day of week
Saturday or Sunday	2982	340 (11%)	1.00 (0.91–1.11)	0.9
Monday-Friday	8155	944 (12%)	1.0

Month
July or August	1897	219 (12%)	0.95 (0.85–1.07)	0.4
Other	9240	1065 (12%)	1.0

Epoch
After duty-hour restrictions	5847	647 (11%)	0.99 (0.84–1.19)	0.9
Before duty-hour restrictions	5290	637 (12%)	1.0

Relative risks and p-values are from a modified Poisson regression model that included the four timing of birth indicators as well as study center, BW, GA, sex, race, multiple birth, 1-minute Apgar score < 5, maternal antepartum hemorrhage, maternal hypertension or preeclampsia-eclampsia, and continuous time (to adjust for common time trends).