Since writing my book back in 2006, there have been substantial changes in the thought process that goes into “induction” of post -date pregnant women . At that time induction was recommended at 10 days post term , so once a patient had reached her 40th week , she would be induced on the tenth day that followed. Things were reassessed and new criteria looked at incidence of complications resulting from induction and from not doing induction and a new mind set evolved that resulted in induction being done earlier, at day 7 post dates.
The deciding factor for the due date was complicated. If a patient was certain of her Last Menstrual Period (L.M.P.) and an early ultrasound established that the gestational age was no more than 8 days within the age of the baby calculated from the LMP, the LMP was used to establish the age of the baby and the due date. This would change if the calculated age based on the LMP was greater that 8 days when compared to the ultrasound , in which case we would ignore the LMP and take the age based on the ulrasound as being the more accurate reading and predictor
This has now changed in that we now recognize how accurate an early ultrasound is and we take the early ultrasound over the LMP in calculating the age of the baby, regardless of the discrepancy between the LMP and ultrasound in establishing the gestation of the fetus.
This is why it has become so important in doing an early ultrasound in the first trimester of pregnancy
