If your ultrasound said fetal age is 7 weeks but LMP was 9 ago should you worry?

If your ultrasound indicated a fetal age of 7 weeks while your last menstrual period (LMP) was 9 weeks ago, it is generally not a cause for immediate concern. Discrepancies between the estimated fetal age based on ultrasound measurements and the expected age based on LMP are relatively common. Here are some possible reasons for this difference:

1. Measurement Variability: Ultrasound measurements can be affected by various factors, such as the skill of the sonographer, the quality of the ultrasound equipment, and the position of the fetus. These factors can introduce some variability in the estimated fetal age.

2. Implantation Timing: The timing of embryo implantation after ovulation can vary from person to person. In some cases, implantation may occur a few days later than expected, leading to a slightly younger-appearing fetus on ultrasound compared to the LMP-based estimation.

3. Early Miscalculation: It is possible that your LMP was miscalculated or recalled incorrectly. If your menstrual cycles are irregular, it can be challenging to pinpoint the exact date of ovulation and conception.

4. Differences in Gestational Age Definitions: Gestational age is usually calculated from the first day of the last menstrual period. However, some healthcare providers may use a different method known as "crown-rump length" (CRL) measurement to determine gestational age. Depending on the measurement technique used, there can be slight differences in the estimated fetal age.

5. Misinterpretation of Ultrasound Findings: In rare cases, the ultrasound may be misinterpreted, leading to an inaccurate estimation of fetal age.

If you are concerned about the discrepancy between the ultrasound findings and your LMP, it is advisable to discuss this with your healthcare provider. They can assess the situation, review your medical history, and provide appropriate guidance. In most cases, a slight difference in estimated fetal age does not necessarily indicate an underlying problem with the pregnancy.