How long does it take to detect pregnancy on March 25th of the last menstrual period mainly depends on the detection method, such as blood test HCG (human chorionic gonadotropin) can be detected 7~10 days after intercourse during ovulation, urine pregnancy test or pregnancy test paper can be detected 10~14 days after intercourse or about 35 days after menopause. HCG (human chorionic gonadotropin) is a protein hormone synthesized by the placenta. Generally, 7~10 days after intercourse during ovulation (around April 17th), the fertilized egg will be implanted, and the placenta will start to secrete HCG after implantation, and at this time, an elevated level of HCG can be detected in a blood test, which means that you are pregnant. If the embryo is well-developed, HCG rises rapidly at the rate of doubling every 2 days. 10~14 days after intercourse during ovulation or 35 days after menopause (around April 20), HCG in urine will also rise significantly, and at this time, pregnancy can be detected positively through a urine pregnancy test or a pregnancy test paper, which indicates pregnancy. HCG test by blood or urine test detects pregnancy, but it is not clear whether it is intrauterine pregnancy, but also through the gynecological ultrasound to determine. It is recommended to take a gynecological ultrasound after 40 days of menopause (around April 20) to accurately see whether the pregnancy sac is located in the uterus. If you are not sure whether you are pregnant or not, you can consult your doctor in the hospital and complete the relevant tests.