. 2009 Dec 3;36(2):219–228. doi: 10.1093/schbul/sbp147

Table 2.

Cases of Schizophrenia That Were or Were Not Exposed in Prenatal Life to the 1957 A2 Influenza Pandemic in Uusimaa County, Finland

Time of Birth	Trimester of Gestation^a	Exposed (Born November 15, 1957, to August 14, 1958)			Not Exposed (Born in Corresponding Periods of 6 Previous Years, 1951–1957)			Relative Risk	95% Confidence Interval
Time of Birth	Trimester of Gestation^a	Live Births	Cases of Schizophrenia	Risk Per 1000	Live Births	Cases of Schizophrenia	Risk Per 1000	Relative Risk	95% Confidence Interval
November 15 to February 14	3rd	3419	65	19.0	18 898	513	27.1	0.70	0.54–0.90
February 15 to May 14	2nd	3536	81	22.9	20 775	558	26.9	0.85	0.68–1.07
May 15 to August 14	1st	3288	70	21.3	20 495	494	24.1	0.88	0.69–1.13

Trimester of gestational exposure for exposed cohorts.