Accuracy of Abdominal Ultrasound for Pregnancy Testing at 16 Days - Obstetrics and Gynecology

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The accuracy of abdominal ultrasound for pregnancy testing at 16 days post-conception is generally considered to be low. In your case, where sexual intercourse occurred on December 23 and the ultrasound was performed on January 8 (16 days later), it is important to understand the limitations of abdominal ultrasound in early pregnancy detection.

Abdominal ultrasound is typically not the preferred method for early pregnancy detection. The most reliable way to confirm pregnancy is through a blood test measuring human chorionic gonadotropin (hCG) levels or a home pregnancy test that detects hCG in urine. These tests can usually provide accurate results about a week after a missed period, which is typically around 14 days post-ovulation for women with regular cycles. However, since your girlfriend has irregular menstrual cycles, it complicates the timing of ovulation and conception.

At 16 days post-conception, the embryo is still very small, and the gestational sac may not be visible on an abdominal ultrasound. It is generally accepted that abdominal ultrasound can detect a pregnancy around 5-6 weeks gestation, which is approximately 21-28 days after conception. Therefore, the ultrasound performed at 16 days may not have been able to detect any signs of pregnancy, leading to the conclusion that your girlfriend was not pregnant at that time.

Additionally, the fact that your girlfriend received a shot of a medication to induce menstruation (likely a form of hormonal therapy) suggests that the healthcare provider was trying to manage her menstrual irregularities, which may also affect the timing of her next period. It is not uncommon for women with irregular cycles to experience delays in menstruation even when not pregnant, especially after hormonal treatments.

If your girlfriend's period does not arrive after the administration of the medication, it would be advisable to follow up with her healthcare provider. They may recommend further testing, such as a repeat hCG blood test or a follow-up ultrasound, to monitor her condition and ensure that there are no underlying issues.

In summary, abdominal ultrasound at 16 days post-conception is not considered accurate for detecting pregnancy. For future reference, if there is a concern about pregnancy, it is best to wait until at least 21 days post-ovulation or until a missed period to perform a more reliable test. If there are ongoing concerns about menstrual irregularities or potential pregnancy, consulting a healthcare provider for further evaluation and testing is crucial.