Unless you have IVF or in-vitro fertilization it is necessary to make love and have sex during the 5-6 fertile days leading up to ovulation and the day of ovulation.
Studies have shown that if you want to improve your chances getting pregnant not only do you have to make love during your fertile days, but you also have to make love regularly. Just once during your 5-6 fertile days is not enough.
In a 2001 study published in the New England Journal of Medicine the researchers found that the highest percent of pregnancies were achieved when you made love once every day. Making love every other day still had a good chance getting you pregnant, but it was lower than once every day.
The lowest chance getting pregnant was observed among couples who made love just once during the fertile days.
The researchers recommended that to improve your pregnancy chance you should make love regularly throughout the menstrual cycle 2-3 times a week, every week. And during your fertile days every day or every other day.