is possible only, if unprotected sexual intercourse is done with ejaculation around ovulation time in regular period. Ovulation occurs approx 14 days before due date.
Use ovulation prediction
kit (OPK) to predict ovulation time in corresponds to calculated date. 4-6 days around ovulation time are fertile period.
Avoid stress, take healthy diet with Vit-E & Folic acid
supplements, control body wt and need proper sleep to improve fertility