A baby’s due date given LMP Oct 16.

A baby’s due date given LMP Oct 16.

• A. January 9
• B. March 31
• C. July 23
• D. September 16

Answer: (C)

Gestational dating uses the first day of the last menstrual period to estimate the due date, assuming a 28-day cycle and ovulation around day 14. The due date is about 40 weeks (280 days) from that LMP. With an LMP of October 16, add 9 months to reach July 16, then add 7 days to arrive at July 23. So the due date is July 23. If cycles are irregular or the LMP date is uncertain, early ultrasound dating can adjust this estimate, but based on the standard rule, July 23 is the correct date. The other options fall significantly outside the 40-week window.

Gestational dating uses the first day of the last menstrual period to estimate the due date, assuming a 28-day cycle and ovulation around day 14. The due date is about 40 weeks (280 days) from that LMP. With an LMP of October 16, add 9 months to reach July 16, then add 7 days to arrive at July 23. So the due date is July 23. If cycles are irregular or the LMP date is uncertain, early ultrasound dating can adjust this estimate, but based on the standard rule, July 23 is the correct date. The other options fall significantly outside the 40-week window.