Question

A 28-year-old G1 presents for prenatal care. Her periods have been irregular and she does not recall when the last one occurred. She is healthy and denies any medical problems. The uterus is 10 weeks in size and there are no adnexal masses. At this point in time, what is the best way to date the pregnancy?

1) Qualitative serum hCG
2) Quantitative serum hCG
3) Ultrasound measurement, gestational sac
4) Ultrasound measurement, crown-rump length
5) Uterine size on pelvic exam

Answer 1

To date a pregnancy when the LMP is unknown, an ultrasound measurement of the crown-rump length is considered the most accurate method, particularly between the 7th and 13th weeks of gestation.

Step-by-step explanation:

The best way to date a pregnancy when periods have been irregular and the last menstrual period is unknown is through an ultrasound measurement, specifically, the crown-rump length (CRL). While both qualitative and quantitative serum hCG tests can confirm pregnancy, they do not provide precise gestational age. The uterine size on pelvic exam is a less precise method for dating a pregnancy compared to ultrasound. CRL is considered the most accurate method to date pregnancy between 7 and 13 weeks gestation.