Sample Sizes Necessary to Detect a Two Fold (100%) Increase In Selected Adverse Pregnancy Outcomes

perinatology.com

Home > Reference >Sample Sizes Necessary to Detect

Studies that compare pregnancy outcomes must have an adequate number of subjects to detect a difference between the exposed group and a control group. As the the table below illustrates large sample sizes are necessary to show a twofold increase in adverse pregnancy outcomes. To detect smaller differences requires a larger sample size. To detect moderately common birth defects such as cleft lip or palate requires a sample size that is prohibitive for most controlled studies.

Sample Sizes Necessary to Detect a Two Fold (100%) Increase In Selected Adverse Pregnancy Outcomes (80% power, 5% Level of Significance)
Outcome	Denominator	Population rate	Number of Exposed Pregnancies Needed
Spontaneous Abortion	Enrolled Pregnancies	15/100	266
Low Birth Weight	Live Births	10/100	261
Fetal Death	Live births plus fetal deaths	3/100	684
Any major birth defect	Live Births	3/100	684
Cardiovascular defect	Live Births	1/115	2196
Cleft lip with or without palate	Live births	1/930	17311
Stickler syndrome (or other rare birth defect)	Live births	1/10000	185,539

Adapted from: Draft Guidance for Industry on Establishing Pregnancy Registries . U.S. Department of health and Human Services June , 1999.