Table 1.

Prenatal Risk Factors for Schizophrenia

Risk Factor	Author	Description
(1) Infections*
(A) Influenza	Mednick et al. (1988)21	Most studies that examined the effect of exposure to the 1957 influenza epidemic during pregnancy (2nd trimester) found a relatively increased risk (1.5–2.0) of later developing schizophrenia.
	Kendell and Kemp (1989)22
	O'Callaghan et al. (1991)23
	Torrey et al. (1992)24
	McGrath et al. (1994)25
	Erlenmeyer-Kimling et al. (1994)26
	Izumoto et al. (1999)27
(B) Other infections	Brown et al. (2000a)28	2nd-trimester exposure to a wide variety of respiratory infections was associated with a significantly increased risk of schizophrenia spectrum disorders (adjusted relative risk 2.13).
	Brown et al. (2000b)29	1st-trimester exposure to rubella led to a substantially higher relative risk (5.2) of developing non-affective psychoses.
	Suvisaari et al. (1999)30	2nd-trimester exposure to poliovirus infection was found to increase the relative risk for the later development of schizophrenia (1.05: 0.99–1.10).
(C) Archived serum	Brown et al. (2004)31	Examination of archived maternal serum showed that the risk of schizophrenia increased sevenfold following influenza exposure during the 1st trimester of pregnancy.
	Brown et al. (2005)32	Maternal exposure to toxoplasmosis increased risk of schizophrenia/schizophrenia-spectrum disorders (OR 2.61:1.00–6.82).
	Buka et al. (2001)33	The offspring of mothers with elevated levels of antibodies to the herpes simplex virus type 2 were found to be at a significantly increased risk for the development of schizophrenia and other psychotic illnesses in adulthood (P = .02).
(2) Medication
	Sorensen et al. (2004)34	Prenatal exposure to analgesics in the 2nd trimester was associated with an increased risk of schizophrenia (OR 4.75:1.9–12.0).
	Sorensen et al. (2003)35	Prenatal exposure to both hypertension and diuretic treatment in the 3rd trimester conferred a 4.01-fold (95% CI = 1.41–11.40) elevated risk.
(3) Nutritional Deficiency
	St. Clair et al. (2005)36	Prenatal exposure to the Chinese famine of 1959–1961 significantly increased risk of schizophrenia in later life (adjusted relative risk: 2.30, 1.99–2.65, for those born in 1960, and 1.93, 1.68–2.23, for those born in 1961).
	Susser and Lin (1992)37	Birth cohorts exposed to the 1944–1945 Dutch
	Susser et al. (1996)38	Hunger Winter in early gestation had a twofold
	Hoek et al. (1996)39	increase in risk for schizophrenia
(4) Stress
	Dalman et al. (2005)40	Paternal death during fetal life was associated with an increased risk of developing psychosis later in life (HR 2.4: 1.4–4.0). This replicates the classic finding of Huttunen and Niskanen (1978).
	Kinney et al. (1999)42	Prenatal exposure to a natural disaster (a severe tornado) during vulnerable weeks of gestation was associated with increased risk of schizophrenia.
	Van Os (1998)43	Increased relative risk of schizophrenia (1.28: 1.07–1.53) among those in the Netherlands who were in utero (1st trimester) during the Nazi invasion in May 1940.
	Myhrman et al. (1996)44	The risk of later schizophrenia among unwanted children was raised compared with wanted or mistimed children, even after adjustment for confounding by sociodemographic, pregnancy, and perinatal variables (OR 2.4:1.2–4.8).
(5) Rhesus Incompatibility
	Hollister et al. (1996)45	The rate of schizophrenia was found to be significantly higher in an Rh-incompatible group (2.1%) compared with the Rh-compatible group (0.8%).

^*See article by Brown, this series, for comprehensive overview of prenatal viral exposure.