Table 1.

Characteristics of mothers delivering singletons in the Pennsylvania birth certificate cohort (2003–2010) and the subcohort of mothers in the validation study.

	Birth certificate data		Validation substudy data
	N	%	N	%
Gestational age at delivery
Term (≥37 weeks)	786,028	92.1	705	58.6
Preterm (<37 weeks)	67,531	7.9	499	41.5
Maternal race-ethnicity
Non-Hispanic white	723,033	84.7	645	53.6
Non-Hispanic black	130,526	15.3	559	46.4
Prepregnancy BMI a
Underweight	35,289	4.1	258	21.4
Normal weight or overweight	637,122	74.6	360	29.9
Obese class 1	100,061	11.7	291	24.2
Obese classes 2 & 3	81,087	9.5	295	24.5
Gestational weight gain c
<20th percentile	163,063	19.1	358	29.7
20–80th percentile	511,453	60.0	449	37.3
>80th percentile	178,495	20.9	397	33.0
Gestational weight gain
Q1 [5.9 kg] b	175,891	20.6	378	31.4
Q2 [11.4 kg]	180,085	21.1	234	19.4
Q3 [14.5 kg]	161,389	18.9	113	9.4
Q4 [18.2 kg]	167,781	19.7	179	14.9
Q5 [23.6 kg]	168,413	19.7	300	24.9
Maternal age
<20	72,222	8.5	171	14.2
20–29	730,304	50.5	640	53.2
≥30	350,442	41.1	393	32.6
Parity
1	415,057	48.8	632	52.7
2	359,740	42.3	449	37.4
3 or more	76,453	8.9	119	9.9
Marital status
Unmarried	311,151	36.5	691	57.4
Married	541,028	63.5	512	42.6
Maternal education
Less than high school	113,945	13.4	188	15.6
High school	231,129	27.2	396	33.0
Some college	235,061	27.6	309	25.7
College graduate	270,623	31.8	308	25.7
Smoking during pregnancy
No	683,869	81.3	921	76.7
Yes	157,501	18.7	280	23.3

^aPrepregnancy body mass index categories were underweight, <18.5 kg/m²; normal weight or 18.5–29.9 kg/m²; obese class 1, 30–34.9 kg/m²; obese classes 2 and 3, ≥35 kg/m².

^bBased on quintiles of the distribution. Values presented in brackets are the median for that category.

^cGestational weight gain was measured using weight-gain-for-gestational-age z-scores ¹⁶.