Table 1. Characteristics of studies from general obstetric populations.

Study	Study Years	Study Design	No. of Participants*	Population	Definition of Exposure	Confounders Adjusted	Definition of Outcome†	Risk‡	Quality§
Exacoustòs et al,17 1993 Italy	1984–1990	Retrospective cohort	12,708 (492/12,216)	Exposed and unexposed reportedly matched by age and parity	Leiomyoma(s) 3 cm in diameter on ultrasound prior to 20 weeks gestation	None	Loss prior to 20 weeks	7.7% v. 6.8%	Good
Mollica et al,16 1996 Italy	1983–1994	Retrospective cohort	2,551 (88/2,463)	Exposed randomized to clinical protocol and matched with unexposed receiving routine obstetric care	Leiomyoma(s) on ultrasound	None	—	13.6% v. 9.3%	Poor
Benson et al,15 2001 USA	1991–1993	Retrospective cohort	858 (143/715)	Exposed and unexposed matched 1:5 by age and parity	Leiomyoma(s) on first trimester ultrasound	None	Loss prior to 25 weeks	14.0% v. 7.6%	Good
Majeed et al,18 2011 Pakistan	2008–2010	Retrospective cohort	200 (100/100)	Exposed matched with random sample of unexposed	Leiomyoma(s) on ultrasound	None	Loss prior to 24 weeks	11% v. 5%	Poor
Hartmann et al,19 2017 USA	2000–2012	Prospective cohort	5,512 (571/4,941)	Women enrolled prior to conception or before 12 weeks gestation	Leiomyoma(s) 0.5 cm on research ultrasound	Maternal age, race/ethnicity, alcohol use, prior terminations, parity	Loss prior to 20 weeks	14.0% v. 10.9%	Good

—, not reported

^*Reported as total (with leiomyomas/without leiomyomas)

^†In definition of outcome, weeks refer to weeks of gestation

^‡Proportion of pregnancies ending in spontaneous abortion exposed versus unexposed

^§Grading based on the Newcastle-Ottawa Scale