It is not uncommon for there to be a slight discrepancy between the estimated gestational age based on ultrasound measurements (sonar) and the calculated gestational age based on your last menstrual period (LMP). The LMP method assumes a regular 28-day cycle with ovulation occurring on day 14, while in reality, cycles can vary and ovulation may occur earlier or later.
Ultrasound measurements are generally considered more accurate in determining gestational age during early pregnancy. However, as pregnancy progresses, individual variations in fetal growth can lead to differences between the two methods.
In your case, if you have been tracking your menstrual cycles accurately and have consistent cycle lengths, it is reasonable to rely on your calculated due date of the 30th. However, it's essential to discuss this discrepancy with your healthcare provider who has access to all relevant information about your pregnancy.
Your healthcare provider may consider other factors such as physical examinations and additional ultrasounds to assess fetal growth and determine an accurate due date. They will also take into account any potential complications or concerns that may affect the timing of delivery.
Remember that due dates are estimates and only serve as a guideline for monitoring fetal development. The actual timing of labor can vary from woman to woman and even from pregnancy to pregnancy.
If you have any further concerns or questions about your due date or fetal development, it's best to consult with your healthcare provider for personalized advice based on your specific situation.