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. Author manuscript; available in PMC: 2014 May 28.
Published in final edited form as: Paediatr Perinat Epidemiol. 2012 Jan 16;26(2):109–116. doi: 10.1111/j.1365-3016.2011.01254.x

Table 2.

Observed associations between gestational weight gain measures and risk of preterm birth, when, by design, gestational weight gain has been simulated to be independent of risk of preterm birth (see text for details). Study population was based on singleton pregnancies with normal-weight prepregnancy body mass index (18.5–24.9 kg/m2) in British Columbia, Canada, between 2000–2009 (n=128 371).

Fifths (quintile groupings) of gestational weight
gain measure		 Total gestational
weight gain (kg)		 Average rate of
gestational weight gain
(kg/week)		 IOM adequacy ratioa
First ORb preterm birth ≤ 32 weeks [95% confidence interval] 4.4 [3.6, 5.4] 1.8 [1.5, 2.2] 1.6 [1.3, 2.0]
ORb preterm birth <37 weeks [95% confidence interval] 2.1 [1.9, 2.2] 1.5 [1.4, 1.6] 1.4 [1.3, 1.5]
Median value of weight gain measurement 10.3 0.27 0.81
Second ORb preterm birth ≤ 32 weeks [95% confidence interval] 2.0 [1.6, 2.5] 1.0 [0.8, 1.2] 1.1 [0.9, 1.3]
ORb preterm birth <37 weeks [95% confidence interval] 1.4 [1.3, 1.5] 1.1 [1.0, 1.2] 1.1 [1.0, 1.2]
Median value of weight gain measurement 14.6 0.38 1.14
Third ORb preterm birth ≤ 32 weeks [95% confidence interval] reference group reference group reference group
ORb preterm birth <37 weeks [95% confidence interval] reference group reference group reference group
Median value of weight gain measurement 17.6 0.45 1.37
Fourth ORb preterm birth ≤ 32 weeks [95% confidence interval] 0.4 [0.3, 0.6] 0.8 [0.6, 1.0] 1.0 [0.8, 1.2]
ORb preterm birth <37 weeks [95% confidence interval] 0.6 [0.6, 0.7] 0.9 [0.8, 1.0] 1.0 [0.9, 1.0]
Median value of weight gain measurement 20.6 0.53 1.60
Fifth ORb preterm birth ≤ 32 weeks [95% confidence interval] 0.2 [0.1, 0.3] 0.7 [0.6, 0.9] 1.3 [1.0, 1.6]
ORb preterm birth <37 weeks [95% confidence interval] 0.3 [0.3, 0.4] 0.8 [0.7, 0.8] 1.0 [0.9, 1.0]
Median value of weight gain measurement 25.0 0.63 1.92
a

Institute of Medicine, IOM1. See text for details on calculation of IOM adequacy ratio

b

OR, odds ratio, in fifth of gestational weight gain compared with the middle fifth