Birth weight estimation

Very quick post - yesterday’s palpation-based fetal weight estimate from the midwife got me thinking.  I pulled this equation from somewhere at some point, but this is the original citation:

Nahum, G. G., & Stanislaw, H. 2002. Validation of a birth weight prediction equation based on maternal characteristics. The Journal of Reproductive Medicine 47(9): 752-760.

General caveats
This equation is only meant to work for:

• Caucasians (or Hispanics, Nahum et al. 2004)
• singleton pregnancies
• no complications (gestational diabetes, blood pressure issues, etc.)
• babies delivered after 37 weeks
• no fetal abnormalities (e.g., chromosomal)
• non-smokers
• women with accurately dated pregnancies

Equation

birth weight (g)
= gestational age (days) 
× [9.38 + (0.264 x fetal gender)
+ (0.000233 × maternal height (cm)
× maternal weight @ 26 weeks (kg))
+ (4.62 × 3rd trimester maternal weight gain rate (kg/day)
× {parity +1})]

where fetal gender = +1 for males, -1 for females, and 0 when gender is not known;
gestational age = days since LMP
parity = number of previous pregnancies

Also, this equation has an average margin of error around 8%.

So for 252 days gestational age (today) and my height, 26 week weight, and 3rd tri rate of weight gain, this baby girl is currently estimated to be 2.955kg, or 6lbs 8.2oz, plus or minus ~8oz.  That said, also remember that I do not currently fit one of the criteria, since I am only at 36w1d.

For a full term pregnancy (280 days), this equation estimates 3.284kg, or 7lbs 3.8oz, plus or minus ~9oz.

Take home message - this equation gives approximately the same estimate that she did!

Isn’t science grand? :)