first of all you need to have an estimate of the prevalence in the population which can be referred to the previous report. If there is no report, you need to perform a pilot study for example in 100 pregnant women. Then you can use known formula to estimate the point prevalence in the population using software like STATA

Thank you

If you want to learn if your sample size enough for your study or not, you should use minitab packet program for pwoer analysis. But if you want to calculate your carriers, affected or normal sample frequenciesin your study population you could use SPSS packet programme or epi info programme.

I am also agree with Mohammad-Sadegh Fallah as after knowing prevalence you can use formula 4pq/e2 or follow online free stats software.

Thank you for every one