Conception of a child is a sacrament that is not given to a person to know. Until a certain period of time, a woman may not even guess that she is carrying a child. When the fact of pregnancy is confirmed, the arising desire to find out when conception occurred is quite natural. Unfortunately, all methods for determining the day of conception are not accurate, but you can calculate the approximate date.
If during the previous menstrual cycle, you had a basal temperature graph, measuring your rectal temperature daily and at the same morning time, then it should have reflected a sharp jump in temperature before the expected ovulation. This means conception could have occurred either on the day of ovulation or +/- 2 days before or after ovulation. The egg cell remains viable for 12-24 hours after ovulation and is capable of fertilization. Ideally, it is necessary to mark the days on which intercourse took place. Also, if the conception of a child was planned, it is necessary to make notes about the change in well-being during the menstrual cycle. This contributes to a more accurate calculation of the date of the onset of ovulation, and therefore the day when the child could be conceived.
A blood test for the hormone hCG (human choriotic gonadotropin) will help determine the duration of pregnancy. The essence of the analysis is that after the onset of pregnancy, the woman's body begins to actively produce this hormone. It increases hundreds of times from week to week. So, at 1-2 weeks, the level of hCG in the blood reaches 150 mU / ml, while by the end of the 8th week it is already about 70,000 mU / ml. If the pregnancy goes well, then this diagnosis allows you to fairly accurately determine the gestational age. If the content of the hormone does not correspond to the period, then this may indicate the presence of any pathology that interferes with the correct development of the fetus, although, of course, minor errors are allowed in one direction or another, but no more than +/- 1 week. For the analysis for hCG, it is necessary to donate blood from a vein on an empty stomach. Having received information about how long you are pregnant, you can calculate the approximate date of conception within the week during which this may have happened.
An ultrasound scan of a pregnant woman's uterus will also help determine the current gestational age by the size of the fetus. The error of this method is large and can be +/- 1-2 weeks, since the gestation of the fetus is uneven. The most accurate diagnosis is made during the first 1-6 weeks of pregnancy. If you manage to undergo an ultrasound scan during this period, then you can find out the date of conception with an error of about 3-5 days.