VBAC EDD blah
EDD or EDB - expected due date, date of delivery, date of birth
VBAC - vaginal birth after c-section
It’s a common question - when is the baby due? And what happens if my pregnancy goes longer than the expected period?
Well, firstly let’s consider how a "due date" is calculated and what it means. Most are calculated using Naegele’s Rule which adds a year to the woman’s last period, subtracting three months and adding seven days to that date. It assumes that the cycle is 28 days, that 9 months = 281 days (ie about 30 days in the calendar months between those dates) and also that the gestation period is average at 40 weeks. Given that full term is anywhere between 37 and 42 weeks though, this is just the centre of the period where the baby may decide to make an entrance.
Wood’s method:
nullips: LMP + 1 year - 2 months - 14 days, +/- days cycle varies from 28 days
multips: LMP + 1 year - 2 months - 18 days , +/- days cycle varies from 28 days
Nichols, Carol Wood, "Postdate Pregnancy, Part II: Clinical Implications," J. of Nurse-Midwifery, Vol. 30, No. 5, Sept/Oct., 1985, pp. 259-268.
Mittendorf’s Study
31 nullips, 83 multips found first pregnancies lasted on average 288 days and multips 283.
Nullips: LMP -3 months + 15 days (adjust for variation in cycle length)
Multips: LMP -3 months +10 days etc . . .
Mittendorf, R. et al., "The length of uncomplicated human gestation," OB/GYN, Vol. 75, No., 6 June, 1990, pp. 907-932.
So if you had someone with a last period starting on 08/07 and a 28 day cycle, my obs wheel would tell me 14/04, Wood’s rule gives a date of 24/04 and Naegele’s rule gives a date of 15/04! So if you’re promised a VBAC if you go into labour before your due date, when you may never have had a vaginal birth before so you can be 10 days behind the mark before you can even think about being ready for labour. So yes, your ob or midwife is just humouring you.
Me bitter much about a recent experience? Yes, yes I am.
