How long after intercourse a pregnancy test can be taken depends on the method of pregnancy test used and needs to be analyzed on a case-by-case basis. At present, there are three main clinical methods for pregnancy testing: 1. The earlier and more accurate method to detect pregnancy is the blood HCG test, which can be detected generally about 10 days after intercourse; 2. Ultrasonography can be performed about 3 weeks after intercourse during ovulation, and only if a pregnancy sac is found in the uterine cavity under ultrasound, intrauterine pregnancy can be diagnosed. Therefore, there are some differences in the time when a pregnancy test can be performed after intercourse with different testing methods. It should be noted that women with irregular menstrual cycles or long menstrual cycles have different timing of ovulation and ovulation phase, and the rate and amount of HCG secretion starts are also inconsistent, so it is recommended to confirm by testing blood HCG early after intercourse for relatively more accurate results.