Many expectant mothers can tell down to the day when the child was conceived. But they don’t understand why the doctor writes in the exchange card the gestational age is much longer than the patient expects. Why? Are doctors really wrong? The fact is that the duration of the current pregnancy is counted not from the day of conception, but from the day when the expectant mother began her last period with a regular menstrual cycle.
Let's look at this with a simple example. The woman started her period on March 1st. On March 15 (mid-cycle) she became pregnant. What pregnancy date will the doctor estimate on April 20? The doctor will count from the first day of the last “critical days” and write the period 7 weeks 1 day. This will be an obstetric period. And the embryonic period is calculated from the date of conception. And in this case it is 5 weeks 1 day.
Therefore, there is no need to argue with the doctor and prove that you are right. You just need to know that in obstetrics it is customary to indicate the obstetric gestational age in documents.
That is, the difference between obstetric and embryonic periods is approximately two weeks, if 28 days pass between periods (from the first day to the first). It happens that a woman’s cycle lasts not 28 days, but 33-35 days. In this case, the doctor will take this point into account when determining the gestational age and when calculating the expected date of birth of the baby.