We are preparing to perform a cohort study evaluating smoking during pregnancy and preeclampsia. We would like to know how many subjects need to be recruited to detect a relative risk of 1.5 with 90% power and a 1% significance threshold assuming a two-sided test. Previous evidence suggests that 10% of pregnancies experience preeclampsia and that we can expect a ratio of those that smoke compared to those that do not smoke during pregnancy to be 0.4. What is the total cohort sample size needed?