Table of contents:
- Is it possible to get pregnant using birth control?
- What is menstruation like for those who take contraceptives

Whoever takes contraceptives every day, always at the same time, does not have a fertile period and, therefore, does not ovulate, reducing the chance of becoming pregnant, because, as there is no mature egg, it cannot be fertilized. This occurs both with 21, 24 or 28 day contraceptives, and also with contraceptive implants.
Oral contraceptives inhibit ovulation, but also alter the uterine endometrium and cervical mucus, enhancing the prevention of pregnancy. However, if a woman forgets to take a pill, especially in the first week of the pack, there is a chance of getting pregnant because she can ovulate and release an egg that, when meeting the sperm, can survive inside the woman for 5 up to 7 days, it can be fertilized.

See how to use the pill and not get pregnant in: How to take birth control correctly.
Is it possible to get pregnant using birth control?
Despite being a very effective contraceptive method, a woman can get pregnant using the contraceptive if:
1. Forgetting to take the pill daily at the same time. There are greater chances if the forgetfulness happens in the first week of the card.
2. Taking any medication that decreases the effectiveness of the pill, such as antibiotics, immunosuppressants and anticonvulsants, for example, because they cut the pill's effect. See some examples in: Remedies that decrease the effectiveness of the pill.
3. Vomiting or having diarrhea within 2 hours of taking the pill.
In these cases, pregnancy would be possible, as the woman may ovulate and, when having intercourse, the egg is fertilized.
Furthermore, the pill has a 1% failure rate, so it is possible to get pregnant even if you take the contraceptive pill correctly every month, but this doesn't happen often.
See how to calculate your fertile period:
What is menstruation like for those who take contraceptives
The menstruation that comes every month, for those who take the contraceptive, does not refer to the "nest" prepared by the body to receive the baby, but the result of hormonal deprivation during the interval between one pack and another.
This false period tends to cause less cramping and lasts less days, and thanks to the effectiveness of the contraceptive pill, you can have sex every day of the month, even during the break days between one pack and another, without running the risk of becoming pregnant, as long as the pill is used correctly.
Whoever takes the contraceptive correctly may notice some changes in the days before menstruation, such as sore breasts, increased irritability and body swelling, which are known as premenstrual tension - PMS, but these symptoms are milder than if the woman does not take the contraceptive pill.
Taking contraceptives correctly does not exclude the need to use condoms during sexual intercourse because only condoms protect against sexually transmitted diseases. See: What to do if you had sex without a condom.