Postmenstrual gestational age should be used with care in studies of early human hematopoietic development.

摘要

The hematopoietic system undergoes rapid changes during embryogenesis; therefore, studying this process requires accurate embryo staging. In the mouse, timed pregnancies can routinely be set and controlled; however, accurate staging of human pregnancies is more problematic, compounded by different ways that gestational age is assessed. Although developmental biologists calculate gestational age based on the woman's last ovulation (postovulatory gestational age), clinicians evaluate it from the first day of the last menstrual period (postmenstrual gestational age), using ultrasound measurement of crown-rump length.1 Recording the postmenstrual gestational age of the human embryo largely meets the needs of the medical care. However, it will exceed postovulatory gestational age, which is the true developmental age of the embryo, by 2 weeks in the normal case of a regular menstrual cycle with mid-cycle ovulation and may differ by an unknown duration when the date of ovulation is unknown, which is almost always the case. These ambiguities in gestational age determination introduce significant discrepancies in research into early human embryogenesis.2