Table 1. Characteristics of Included Studies With and Without a Comparison Group Evaluating Risk of Spontaneous Abortion, Congenital Defects, Stillbirth, or Preterm Birth With Smallpox Vaccination in Pregnancy.

Study	Year	Country	Study Design	Inclusion Criteria	Vaccinated in Pregnancy	Vaccinated in First Trimester	Unexposed (n=33,487)	Level of Evidence*
Studies Including a Comparison Group					n=10,825	n=6,040
Ryan et al12	2008	U.S.	Retrospective cohort	Military women vaccinated during pregnancy	882	672	Military women with no history of smallpox vaccination, n=23,685	II
Naderi et al8	1975	Iran	Prospective cohort	Registered pregnant women vaccinated during mass vaccination program	1,522	211	Nonvaccinated pregnant women in same institution during the year after mass vaccination program, n=2,024	II
Ladnyi et al19	1974	Russia	Prospective cohort	Registered pregnant women vaccinated during mass vaccination program	1,172	366	Pregnant women seen during interepidemic period not vaccinated during pregnancy, n=777	II
Rajhvajn et al20	1973	Croatia	Retrospective survey	Pregnant women conceived before mass vaccination reporting vaccination up to fourth month of pregnancy	257		Pregnant women conceived before mass vaccination who were not vaccinated during pregnancy, n=266	II
Janiszewski et al21	1966	Poland	Retrospective cohort	Pregnant women vaccinated during pregnancy	205	193	Pregnant women during the same time period who were not vaccinated, n=694	II
Bourke et al22	1964	Ireland	Prospective cohort	Registered pregnant women vaccinated during smallpox outbreak	122	54	Pregnant women not vaccinated during pregnancy seen for first prenatal visit on same day as exposed (four adjacent charts), n=448	II
Liebeschuetz et al23	1964	England	Prospective cohort	Pregnant women less than 5 mo vaccinated during mass vaccination program	157	126	Pregnant women not vaccinated during pregnancy, n=1,657	II
Abramowitz et al28	1957	South Africa	Retrospective cohort	Pregnant women less than 20 wk of gestation vaccinated during smallpox outbreak	1,121		Pregnant women not vaccinated during pregnancy, n=201	II
Bieniarz et al7	1956	Poland	Retrospective cohort	Pregnant women vaccinated during mass vaccination	495		Pregnant women not vaccinated during pregnancy, n=1,376	II
Bellows et al24	1949	U.S.	Prospective cohort	Registered pregnant women vaccinated during mass vaccination program	720	246	Pregnant women not vaccinated during pregnancy, n=173	II
Greenberg et al29	1949	U.S.	Retrospective cohort	Pregnant women with viable neonate who were vaccinated at less than 3 mo during mass vaccination program	4,172	4,172	Pregnant women in same clinic or hospital who were not vaccinated, n=2,186	II
Studies Without a Comparison Group					n=1,376	n=331
Ryan et al11	2008	U.S.	Prospective registry	Military women vaccinated during pregnancy	208	203	NA	II
Topciu et al30	1976	Romania	Prospective cohort	Pregnant women vaccinated during pregnancy	608 (46)†	7†	NA	III
Krstajic et al25	1973	Croatia	Prospective cohort	Pregnant women vaccinated during pregnancy	26 (11)†	11†	NA	III
Engstrom et al26	1966	Sweden	Prospective cohort	Pregnant women (nurses, professionals, hospital patients, those traveling abroad) vaccinated during pregnancy	170	19	NA	III
Wentworth et al31	1966	Wales	Retrospective cohort	Pregnant women vaccinated during smallpox outbreak at the time a continuous series of placentas were being collected	65	56	NA	III
MacArthur et al6	1952	Scotland	Retrospective survey	Pregnant women reporting vaccination during pregnancy at time of outbreak	170	34	NA	III
Urner et al27	1925	U.S.	Prospective cohort	Registered pregnant women vaccinated during smallpox outbreak	129	1	NA	III

NA, not applicable.

^*Level of evidence: I, a randomized, controlled trial; II, a cohort or case-controlled study that includes a comparison group; III, an uncontrolled descriptive study including case series.

^†Excludes women who underwent abortion or had an early pregnancy loss.