Vasectomy

http://healthlibrary.brighamandwomens.org/Search/85,P00731

http://en.wikipedia.org/Vasectomy

Women's Health Disorders

http://healthlibrary.brighamandwomens.org/Search/85,P00551

Calculating a Due Date

http://healthlibrary.brighamandwomens.org/Search/85,P01209

http://en.wikipedia.org/wiki/Pregnancy#Determining_the_start_of_pregnancy_and_predicting_date_of_birth