Severe obesity, gestational weight gain, and adverse birth outcomes

Abstract

Background: The 2009 Institute of Medicine (IOM) Committee to Reevaluate Gestational Weight Gain Guidelines concluded that there were too few data to inform weight-gain guidelines by obesity severity. Therefore, the committee recommended a single range, 5-9 kg at term, for all obese women.

Objective: We explored associations between gestational weight gain and small-for-gestational-age (SGA) births, large-for-gestational-age (LGA) births, spontaneous preterm births (sPTBs), and medically indicated preterm births (iPTBs) among obese women who were stratified by severity of obesity.

Design: We studied a cohort of singleton, live-born infants without congenital anomalies born to obesity class 1 (prepregnancy body mass index [BMI (in kg/m(2))]: 30-34.9; n = 3254), class 2 (BMI: 35-39.9; n = 1451), and class 3 (BMI: > or =40; n = 845) mothers. We defined the adequacy of gestational weight gain as the ratio of observed weight gain to IOM-recommended gestational weight gain.

Results: The prevalence of excessive gestational weight gain declined, and weight loss increased, as obesity became more severe. Generally, weight loss was associated with an elevated risk of SGA, iPTB, and sPTB, and a high weight gain tended to increase the risk of LGA and iPTB. Weight gains associated with probabilities of SGA and LGA of < or =10% and a minimal risk of iPTB and sPTB were as follows: 9.1-13.5 kg (obesity class 1), 5.0-9 kg (obesity class 2), 2.2 to <5.0 kg (obesity class 3 white women), and <2.2 kg (obesity class 3 black women).

Conclusion: These data suggest that the range of gestational weight gain to balance risks of SGA, LGA, sPTB, and iPTB may vary by severity of obesity.

FIGURE 1

Distribution of gestational weight (Wt)-gain categories by severity of obesity. IOM recs, Institute of Medicine recommendations.

FIGURE 2

Adjusted predicted probabilities for 4 adverse birth outcomes among obesity class 1 women (n = 3254). The sample size in each weight (Wt)-gain category was as follows: <0%, n = 111; 0% to 35%, n = 144; 35% to <77%, n = 203; 77% to 140%, n = 443; 141% to <211%, n = 813; 211% to <281%, n = 733; 281% to <352%, n = 430; and ≥352%, n = 377. The following factors were held constant: non-Hispanic white race-ethnicity, nulliparous, nonsmoker, >12 y education, and height = 64 in. SGA, small-for-gestational-age; LGA, large-for-gestational-age; iPTB <37, medically indicated preterm birth at <37 wk gestation; sPTB <37, spontaneous preterm birth at <37 wk gestation; IOM, Institute of Medicine.

FIGURE 3

Adjusted predicted probabilities for 4 adverse outcomes among obesity class 2 women (n = 1451). The sample size in each weight (Wt)-gain category was as follows: <0%, n = 123; 0% to 35%, n = 90; 35% to <77%, n = 140; 77% to 140%, n = 276; 141% to <211%, n = 325; 211% to <281%, n = 245; 281% to <352%, n = 132; and ≥352%, n = 120. The following factors were held constant: non-Hispanic white race-ethnicity, nulliparous, nonsmoker, >12 y education, and height = 64 in. SGA, small-for-gestational-age; LGA, large-for-gestational-age; iPTB <37, medically indicated preterm birth at <37 wk gestation; sPTB <37, spontaneous preterm birth at <37 wk gestation; IOM, Institute of Medicine.

FIGURE 4

Adjusted predicted probabilities for 3 adverse outcomes among obesity class 3 white women (A; n = 568) and obesity class 3 black women (B; n = 277). The sample size in each weight (Wt)-gain category was as follows: <0% (n = 86 white, n = 42 black); 0% to 35% (n = 53 white, n = 28 black); 35% to <77% (n = 74 white, n = 35 black); 77% to 140% (n = 100 white, n = 43 black); 141% to <211% (n = 113 white, n = 63 black); 211% to <281% (n = 67 white, n = 19 black); 281% to <352% (n = 45 white, n = 23 black); and ≥352% (n = 30 white, n = 24 black). The following factors were held constant: nulliparous, nonsmoker, >12 y education, and height = 64 in. We could not study spontaneous preterm birth because there were too few cases. The test of effect modification by race was significant (P < 0.0001). SGA, small-for-gestational-age; LGA, large-for-gestational-age; iPTB <37, medically indicated preterm birth at <37 wk gestation; IOM, Institute of Medicine.