Table 2.

Distribution of estimated fetal weight and birth weight (N = 8,162)

	Gestational age (weeks)	Mean (g)	Standard deviation (g)	Coefficient of variation (%)	90% reference interval
Estimated fetal weighta	20	326	29	9.1	(277; 374)
	28	1,201	124	10.3	(998; 1,405)
	36	2,568	291	11.3	(2,091; 3,046)
Birth weightb	40	3,443	447	13.0	(2,710; 4,176)

^aThe unadjusted reference for estimated fetal weight is described by: mean estimated fetal weight = 13,735 − 5.4340 × 10⁷ × GA⁻² + 4.2970 × 10⁷ × GA⁻² × log(GA) − 0.88865 × 10⁷ × GA⁻² × (log(GA))²

Standard deviation for estimated fetal weight = −24.659 + 0.00677 × GA³

^bThe unadjusted equation for birth weight, between a gestational age of 36–44 weeks, is described by: mean birth weight = 3,443 + 178 × (GA − 40)