Here are some more:
Frye, "Holistic Midwifery" pp. 364-7 supports 4 or 5.
Wood's method:
nullips: LMP + 1 year - 2 months - 14 days, +or- days cycle varies from 28 days
multips: LMP + 1 year - 2 months - 18 days etc . . .
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.
From:
http://www.gentlebirth.org/archives/dueDates.html (great site! BTW)
So using the standard Dr's wheel, I am due 11/15.
Using Mittendorf's Study, I am due 11/19.
Using Woods method, I am due 11/21.
Interesting. Kinda makes you wonder why so many women are being induced for postdates. Maybe if the Drs used a different method, then maybe these mamas wouldn't be pressured so much, so often! Not to mention, the Dr's wheel doesnt take cycle length into consideration either.