Pre-Pregnancy Body Mass Index, Gestational Weight Gain, and Other Maternal Characteristics in Relation to Infant Birth Weight

Ihunnaya O. Frederick; Michelle A. Williams; Anne E. Sales; Diane P. Martin; Marcia Killien

Matern Child Health J. 2008;12(5):557-567.

Conclusion

Our study results, taken together with existing literature, suggest an independent role of pre-pregnancy BMI as a determinant of infant birth weight, as well as complex relationships between pre-pregnancy BMI, gestational weight gain, and other maternal factors with fetal growth, as measured by size at birth. The results are of public health importance because pre-pregnancy BMI and gestational weight gain are modifiable risk factors of adverse pregnancy outcomes.

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Acknowledgments

We would like to acknowledge participants of the Omega Study for their voluntary participation in the study. The authors would like to thank Center for Perinatal Studies staff for their expert technical assistance.

Funding information

This research was supported in part by an award from the National Institutes of Health (HD 32562).

Reprint Address

Ihunnaya O. Frederick, Email: ihunnaya.frederick@swedish.org

Springer Science+Business Media

Cite this: Pre-Pregnancy Body Mass Index, Gestational Weight Gain, and Other Maternal Characteristics in Relation to Infant Birth Weight - Medscape - Sep 01, 2008.

Table 1. Selected Characteristics of the Study Cohort According to Categories of Infant Birth Weight, Seattle and Tacoma, Washington, 1996-2004 ( n = 2,670)
Categories of infant birth weight (g)	LBW <2,500	Normal birth weight 2,500-3,999	Macrosomia ≥4,000	Total
Categories of infant birth weight (g)	n = 116	n = 2164	n = 390	n = 2670
Characteristics	%	%	%	%
Maternal age (years)
<20	1.7	0.5	0.8	0.6
20-34	60.3	65.2	68.2	65.5
35-39	23.3	24.4	22.1	24.0
≥40	10.3	5.0	5.9	5.4
Missing	4.3	4.9	3.1	4.6
Maternal race/ethnicity
White/non-Hispanic	63.8	68.3	70.0	68.4
African American	1.7	1.2	2.3	1.4
Hispanic or Latina	1.7	2.2	3.3	2.4
Asian	6.9	6.0	4.6	5.8
Other/unknown	25.9	22.2	19.7	22.0
Nulliparous	69.0	62.7	59.5	62.5
Unmarried	10.3	8.2	9.5	8.5
Less than high school education	6.0	3.6	5.9	4.0
Smoked during pregnancy	6.0	5.7	6.7	5.9
No prenatal vitamins	0.0	2.7	2.6	2.5
Preterm birth (<37 weeks)	78.4	6.2	0.3	8.5
Infant gender (female)	56.0	52.5	34.9	50.1
Gestational diabetes	5.2	4.6	5.9	4.8
Preeclampsia	20.7	3.6	4.1	4.4
Annual household income (US $)
<30,000	6.0	3.3	3.8	3.5
30,000-69,999	17.3	21.1	22.8	21.2
≥70,000	69.8	68.0	66.9	67.9
Not reported	1.7	2.0	2.1	2.0
Missing	5.2	5.5	4.4	5.3
Gestational weight gain (kg)
≤Median	74.1	49.5	31.8	48.0
>Median	19.8	44.3	63.8	46.1
Missing	6.0	6.2	4.4	5.9
Mean ± SD ^a
Pre-pregnancy BMI (kg/m²)	23.9 ± 6	23.3 ± 5	24.9 ± 6	23.6 ± 5
Maternal age (years)	32.6 ± 6	32.4 ± 4	32.3 ± 5	32.4 ± 5
Gestational weight gain (kg)	13.0 ± 7	16.0 ± 6	18.5 ± 7	16.3 ± 6
Rate of gestational weight gain (kg/week)	0.39 ± 0.2	0.43 ± 0.2	0.53 ± 1.2	0.44 ± 0.5
Gestational age at delivery (weeks)	32.8 ± 4.6	37.6 ± 3.0	38.7 ± 2.8	37.6 ± 3.3
Median [IQR]^b
Gestational weight gain (kg)	12.7 [9.5-15.9]	15.9 [12.7-19.1]	18.2 [12.3-22.3]	15.9 [12.7-19.5]

^a SD = Standard deviation
^b IQR = Interquartile range

Table 2. Infant Birth Weight According to Categories of Pre-pregnancy BMI in Relation to the IOM Gestational Weight Gain Guidelines of 1990
Pre-pregnancy BMI (kg/m²)/IOM weight gain guidelines	Infant birth weight (g)
	LBW	Normal	Macrosomia	Total
	<2,500	2,500-3,999	≥4000	All births
	n (%)^a	n (%)^a	n (%)^a	n (%)^b
<19.8 (Lean)
Below	9 (9.7)	84 (90.3)	0 (0.0)	93 (23.7)
Within	8 (4.5)	157 (88.7)	12 (6.8)	177 (45.0)
Above	4 (3.3)	101 (82.1)	18 (14.6)	123 (31.3)
P-trend*	0.045	0.064	<0.001
19.8-26.0 (Average)
Below	21 (9.9)	185 (86.9)	7 (3.3)	213 (13.1)
Within	27 (4.9)	464 (84.8)	56 (10.2)	547 (33.6)
Above	15 (1.7)	672 (77.3)	182 (20.9)	869 (53.3)
P-trend*	<0.001	<0.001	<0.001
26.1-29.0 (Overweight)
Below	1 (6.7)	13 (86.7)	1 (6.7)	15 (7.3)
Within	3 (8.6)	25 (71.4)	7 (20.0)	35 (17.0)
Above	5 (3.2)	121 (77.6)	30 (19.2)	156 (75.7)
P-trend*	0.223	0.820	0.374
>29.0 (Obese)
Below	4 (8.2)	35 (71.4)	10 (20.4)	49 (17.3)
Within	4 (6.8)	47 (79.7)	8 (13.6)	59 (20.8)
Above	8 (4.6)	125 (71.4)	42 (24.0)	175 (61.8)
P-trend*	0.298	0.708	0.320

* P-value test for linear trend (does not include missing)
^a Row percentages
^b Column percentages. Percentages do not include missing

Table 3. Estimated Regression Coefficients and P-values of the Relationship Between Infant Birth Weight and Predictors of Interest, Seattle and Tacoma, Washington, 1996-2004
Parameter	β	SE (β)	P-value
Constant	2882.81	199.23	<0.001
Pre-pregnancy BMI (kg/m²)	44.67	13.30	0.001
Pre-pregnancy BMI²	−0.51	0.23	0.029
Maternal age (years)	0.87	2.35	0.710
Race/ethnicity (white is referent)
African American	−66.25	79.89	0.407
Hispanic	52.77	68.44	0.441
Asian	−98.77	41.28	0.017
Other	−36.80	25.09	0.143
Less than high school	28.61	55.46	0.606
Preterm birth	−965.40	44.60	<0.001
Nulliparity	−48.57	20.05	0.015
Infant gender (female)	−168.74	19.06	<0.001
Unmarried	−14.56	38.15	0.703
Smoked during pregnancy	49.92	44.84	0.266
Gestational diabetes	28.41	50.11	0.571
Preeclampsia	−136.05	60.48	0.025

Pre-pregnancy BMI entered as continuous variables
Adjusted R² = 0.273
β = estimated coefficient; SE(β) = standard error of the estimated coefficient; CI = Confidence Interval

Table 4. Relative Risk (RR) and 95% Confidence Interval (CI) of Low Birth Weight and Macrosomia According to Pre-pregnancy BMI and Gestational Weight Gain, Seattle and Tacoma, Washington, 1996-2004 ^a
Measurement	Normal BW (N = 2,029)	LBW^b (N = 109)				Macrosomia^b (N = 373)
Measurement	n (%)	n (%)	Unadjusted RR (95% CI)	Adjusted RR (95% CI)	Adjusted RR (95% CI)	n (%)	Unadjusted RR (95% CI)	Adjusted RR (95% CI)	Adjusted RR (95% CI)
Pre-pregnancy BMI (kg/m²)
<19.8	342 (16.9)	21 (19.3)	1.27 (0.79-2.05)	1.51 (1.02-2.25)	1.54 (1.04-2.29)	30 (8.0)	0.52 (0.36-0.74)	0.50 (0.35-0.71)	0.55 (0.38-0.79)
19.8-26.0	1321 (65.1)	63 (57.8)	Referent	Referent	Referent^c	245 (65.7)	Referent	Referent	Referent^c
26.1-29.0	159 (7.8)	9 (8.3)	1.18 (0.60-2.32)	1.03 (0.59-1.80)	1.01 (0.58-1.77)	38 (10.2)	1.23 (0.91-1.68)	1.11 (0.81-1.52)	1.15 (0.84-1.57)
>29.0	207 (10.2)	16 (14.7)	1.58 (0.93-2.68)	0.72 (0.46-1.13)	0.61 (0.37-1.01)	60 (16.1)	1.44 (1.12-1.85)	1.39 (1.08-1.79)	1.65 (1.29-2.11)
Trend P-value			<0.001	<0.001	<0.001		<0.001	<0.001	<0.001
Gestational weight gain (kg)
≤Median (≤15.9)	1071 (52.8)	86 (78.9)	3.17 (2.02-4.98)	1.88 (1.23-2.88)	2.04 (1.34-3.11)	124 (33.2)	0.50 (0.41-0.61)	0.52 (0.43-0.64)	0.49 (0.40-0.60)
>Median (>15.9)	958 (47.2)	23 (21.1)	Referent	Referent	Referent^d	249 (66.8)	Referent	Referent	Referent^d
IOM Gestational weight gain guidelines
Below	317 (15.6)	35 (32.1)	1.74 (1.13-2.68)	1.24 (0.85-1.80)	1.26 (0.88-1.82)	18 (4.8)	0.50 (0.31-0.82)	0.53 (0.33-0.87)	0.49 (0.31-0.78)
Within	693 (34.2)	42 (38.5)	Referent	Referent	Referent^d	83 (22.3)	Referent	Referent	Referent^d
Above	1,019 (50.2)	32 (29.4)	0.53 (0.34-0.84)	0.71 (0.49-1.05)	0.72 (0.49-1.06)	272 (72.9)	1.97 (1.57-2.48)	1.89 (1.50-2.38)	1.76 (1.40-2.22)
Trend P-value			<0.001	<0.001	<0.001		<0.001	<0.001	<0.001

^a Models adjusted for maternal age, race/ethnicity, parity, education, marital status, smoking status, preterm birth, infant gender, gestational diabetes, and preeclampsia
^b LBW and Macrosomia were each compared to Normal BW
^c Models adjusted for * above and gestational weight gain
^d Models adjusted for * above and pre-pregnancy BMI

Table 5. Relative Risk (RR) and 95% Confidence Interval (CI) of Low Birth Weight and Macrosomia According to Combined Categories of Pre-pregnancy BMI and Gestational Weight Gain, Seattle and Tacoma, Washington, 1996-2004
Measurement	Normal BW (N = 2,029)	LBW (N = 109)			Macrosomia (N = 373)
Measurement	n (%)	n (%)	Unadjusted RR (95% CI)	Adjusted RR (95% CI)	n (%)	Unadjusted RR (95% CI)	Adjusted RR (95% CI)
Pre-pregnancy BMI & gestational weight gain (eight with median categories, referencing four)
Lean, ≤median gain	201 (9.9)	16 (14.7)	3.38 (1.70-6.72)	2.97 (1.63-5.43)	9 (2.4)	0.20 (0.10-0.39)	0.20 (0.10-0.38)
Lean, >median gain	141 (7.0)	5 (4.6)	1.57 (0.58-4.25)	1.66 (0.75-3.65)	21 (5.6)	0.61 (0.40-0.93)	0.61 (0.40-0.93)
Average, ≤median gain	649 (32.0)	48 (44.0)	3.15 (1.78-5.58)	2.07 (1.24-3.46)	63 (16.9)	0.42 (0.32-0.54)	0.44 (0.34-0.58)
Average, >median gain	672 (33.1)	15 (13.8)	Referent	Referent^a	182 (48.8)	Referent	Referent^a
Overweight, ≤median gain	82 (4.0)	8 (7.3)	4.07 (1.78-9.33)	2.01 (0.99-4.11)	17 (4.6)	0.81 (0.51-1.27)	0.76 (0.48-1.22)
Overweight, >median gain	77 (3.8)	1 (0.9)	0.59 (0.08-4.39)	0.75 (0.10-5.66)	21 (5.6)	1.00 (0.67-1.50)	0.91 (0.61-1.35)
Obese, ≤median gain	139 (6.9)	14 (12.8)	4.19 (2.07-8.50)	1.24 (0.66-2.33)	35 (9.4)	0.94 (0.68-1.30)	0.95 (0.68-1.32)
Obese, >median gain	68 (3.4)	2 (1.8)	1.31 (0.31-5.61)	0.71 (0.21-2.43)	25 (6.7)	1.26 (0.88-1.81)	1.21 (0.85-1.71)
Pre-pregnancy & gestational weight gain (eight with median categories, referencing three)
Lean, ≤median gain	201 (9.9)	16 (14.7)	1.07 (0.62-1.85)	1.44 (0.92-2.25)	9 (2.4)	0.48 (0.25-0.96)	0.45 (0.23-0.89)
Lean, >median gain	141 (7.0)	5 (4.6)	0.50 (0.20-1.23)	0.80 (0.39-1.63)	21 (5.6)	1.47 (0.92-2.33)	1.38 (0.86-2.19)
Average, ≤median gain	649 (32.0)	48 (44.0)	Referent	Referent^a	63 (16.9)	Referent	Referent^a
Average, >median gain	672 (33.1)	15 (13.8)	0.32 (0.18-0.56)	0.48 (0.29-0.81)	182 (48.8)	2.41 (1.84-3.15)	2.26 (1.73-2.95)
Overweight, ≤median gain	82 (4.0)	8 (7.3)	1.29 (0.63-2.64)	0.97 (0.54-1.74)	17 (4.6)	1.94 (1.19-3.18)	1.73 (1.04-2.87)
Overweight, >median gain	77 (3.8)	1 (0.9)	0.19 (0.03-1.33)	0.36 (0.05-2.71)	21 (5.6)	2.42 (1.55-3.79)	2.05 (1.31-3.21)
Obese, ≤median gain	139 (6.9)	14 (12.8)	1.33 (0.75-2.35)	0.60 (0.36-0.99)	35 (9.4)	2.27 (1.56-3.32)	2.15 (1.47-3.15)
Obese, >median gain	68 (3.4)	2 (1.8)	0.42 (0.10-1.67)	0.34 (0.11-1.13)	25 (6.7)	3.04 (2.02-4.58)	2.73 (1.83-4.07)

^a Models adjusted for maternal age, race/ethnicity, parity, education, marital status, smoking status, preterm birth, infant gender, gestational diabetes, and preeclampsia

Table 5. Relative Risk (RR) and 95% Confidence Interval (CI) of Low Birth Weight and Macrosomia According to Combined Categories of Pre-pregnancy BMI and Gestational Weight Gain, Seattle and Tacoma, Washington, 1996-2004
Measurement	Normal BW (N = 2,029)	LBW (N = 109)			Macrosomia (N = 373)
Measurement	n (%)	n (%)	Unadjusted RR (95% CI)	Adjusted RR (95% CI)	n (%)	Unadjusted RR (95% CI)	Adjusted RR (95% CI)
Pre-pregnancy BMI & gestational weight gain (eight with median categories, referencing four)
Lean, ≤median gain	201 (9.9)	16 (14.7)	3.38 (1.70-6.72)	2.97 (1.63-5.43)	9 (2.4)	0.20 (0.10-0.39)	0.20 (0.10-0.38)
Lean, >median gain	141 (7.0)	5 (4.6)	1.57 (0.58-4.25)	1.66 (0.75-3.65)	21 (5.6)	0.61 (0.40-0.93)	0.61 (0.40-0.93)
Average, ≤median gain	649 (32.0)	48 (44.0)	3.15 (1.78-5.58)	2.07 (1.24-3.46)	63 (16.9)	0.42 (0.32-0.54)	0.44 (0.34-0.58)
Average, >median gain	672 (33.1)	15 (13.8)	Referent	Referent^a	182 (48.8)	Referent	Referent^a
Overweight, ≤median gain	82 (4.0)	8 (7.3)	4.07 (1.78-9.33)	2.01 (0.99-4.11)	17 (4.6)	0.81 (0.51-1.27)	0.76 (0.48-1.22)
Overweight, >median gain	77 (3.8)	1 (0.9)	0.59 (0.08-4.39)	0.75 (0.10-5.66)	21 (5.6)	1.00 (0.67-1.50)	0.91 (0.61-1.35)
Obese, ≤median gain	139 (6.9)	14 (12.8)	4.19 (2.07-8.50)	1.24 (0.66-2.33)	35 (9.4)	0.94 (0.68-1.30)	0.95 (0.68-1.32)
Obese, >median gain	68 (3.4)	2 (1.8)	1.31 (0.31-5.61)	0.71 (0.21-2.43)	25 (6.7)	1.26 (0.88-1.81)	1.21 (0.85-1.71)
Pre-pregnancy & gestational weight gain (eight with median categories, referencing three)
Lean, ≤median gain	201 (9.9)	16 (14.7)	1.07 (0.62-1.85)	1.44 (0.92-2.25)	9 (2.4)	0.48 (0.25-0.96)	0.45 (0.23-0.89)
Lean, >median gain	141 (7.0)	5 (4.6)	0.50 (0.20-1.23)	0.80 (0.39-1.63)	21 (5.6)	1.47 (0.92-2.33)	1.38 (0.86-2.19)
Average, ≤median gain	649 (32.0)	48 (44.0)	Referent	Referent^a	63 (16.9)	Referent	Referent^a
Average, >median gain	672 (33.1)	15 (13.8)	0.32 (0.18-0.56)	0.48 (0.29-0.81)	182 (48.8)	2.41 (1.84-3.15)	2.26 (1.73-2.95)
Overweight, ≤median gain	82 (4.0)	8 (7.3)	1.29 (0.63-2.64)	0.97 (0.54-1.74)	17 (4.6)	1.94 (1.19-3.18)	1.73 (1.04-2.87)
Overweight, >median gain	77 (3.8)	1 (0.9)	0.19 (0.03-1.33)	0.36 (0.05-2.71)	21 (5.6)	2.42 (1.55-3.79)	2.05 (1.31-3.21)
Obese, ≤median gain	139 (6.9)	14 (12.8)	1.33 (0.75-2.35)	0.60 (0.36-0.99)	35 (9.4)	2.27 (1.56-3.32)	2.15 (1.47-3.15)
Obese, >median gain	68 (3.4)	2 (1.8)	0.42 (0.10-1.67)	0.34 (0.11-1.13)	25 (6.7)	3.04 (2.02-4.58)	2.73 (1.83-4.07)

^a Models adjusted for maternal age, race/ethnicity, parity, education, marital status, smoking status, preterm birth, infant gender, gestational diabetes, and preeclampsia

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Pre-Pregnancy Body Mass Index, Gestational Weight Gain, and Other Maternal Characteristics in Relation to Infant Birth Weight

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