Is it okay to have sex on an unsafe day and then use emergency contraception?

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Hello doctor,
My wife and I want to use contraception by combining ovulation tracking. However, I forgot to follow up since my wife stopped menstruating, but after nearly 2 weeks I started using test strips to determine ovulation. I see the result of the concentration of LH < 2.5. As far as I know, it means that the egg has passed the day of ovulation or hasn't ovulated, so my wife and I have sex but still monitor LH levels. The doctor asked me, if I have sex on an unsafe day, can I use emergency contraception? Thank you doctor.
Horitsu Potter (1995)

Answer
Hello,
To the question "Is it okay to have sex on an unsafe day and then use emergency contraception?", the doctor would like to answer as follows:
Method of contraception by calculating days Ovulation is an unstable and ineffective method of contraception because it depends on a woman's menstrual cycle and the unsafe period around ovulation (effective if menstrual cycles are regular, day signs clear ovulation). In case you and your husband intend to have sex on an unsafe day, then use emergency contraception, it is not recommended because the effectiveness is not high and there may be menstrual disturbances afterwards. The two of you should use other temporary methods that are safer, such as: condoms, vaginal film or vaginal ejaculation.
If you still have questions about the method of contraception by calculating the day of ovulation, you can go to the hospital of Vinmec Health System for further examination and advice. Thank you for trusting and sending questions to Vinmec. Wishing you lots of health.
Best regards!

Answered by Specialist Doctor II Tran Thi Mai Huong - Obstetrician and Gynecologist - Department of Obstetrics and Gynecology - Vinmec Hai Phong International General Hospital