. 2021 Jan 15;41(2):204–211. doi: 10.1038/s41372-020-00912-8

Table 2.

Socio-demographic characteristics of mothers who had preterm and term births in the US—1971–2018.

	Preterm categories
	Extreme preterm		Incidence of extreme preterm (per 1000)	Very preterm		Incidence of very preterm (per 1000)	Moderate-to-late preterm		Incidence of moderate-to-late preterm (per 1000)
	n = 1105,266	Column % = 100		n = 1901,604	Column % = 100		n = 14,769,746	Column % = 100
Age group^a
Under 15 years	7779	0.7	10.6	12,016	0.6	16.3	53,798	0.4	73.1
15–24 years	473,445	42.8	6.7	814,767	42.8	11.5	5776,364	39.1	81.8
25–34 years	485,834	44	5.9	826,227	43.4	10.0	6938,789	47	84.1
35–44 tears	135,839	12.3	5.8	243,325	12.8	10.4	1965,522	13.3	83.8
45–54 years	2369	0.2	5.5	5269	0.3	12.3	35,273	0.2	82.2
Race^a
White	533,138	48.2	5.3	1006,236	52.9	9.9	8576,736	58.1	84.8
Black	349,846	31.7	9.5	495,647	26.1	13.4	2850,916	19.3	77.1
Other	222,282	20.1	6.2	39,9721	21	11.3	3342,094	22.6	94.5
Parity^a
1–2 Children	636,858	57.6	6.2	1105,202	58.1	10.7	8605,875	58.3	83.2
3–5 Children	366,915	33.2	6.0	639,357	33.6	10.5	5107,588	34.6	83.5
6 or more Children	86,309	7.8	7.4	138,297	7.3	11.9	937,190	6.3	80.7
Unknown	15,184	1.4	9.9	18,748	1	12.3	119,093	0.8	77.8
	n = 834,470	% = 100		n = 1457,363	% = 100		n = 11,631,133	% = 100
Weight gain^b
Up to 20 lb.	437,466	52.4	11.3	515,700	35.4	13.4	2904,853	25	75.3
21–30 lb.	95,490	11.4	4.2	231,321	15.9	10.2	1947,271	16.7	85.6
31–40 lb.	58,858	7.1	2.8	186,332	12.8	8.9	1849,212	15.9	88.3
Over 40 lb.	32,581	3.9	2.0	125,846	8.6	7.8	1460,800	12.6	90.2
Unknown	210,075	25.2	5.2	398,164	27.3	9.8	3468,997	29.8	85.1
Diabetes^b
No	792,845	95.1	6.1	1360,922	93.3	10.5	10,809,177	92.9	83.4
Yes	23,186	2.8	3.1	69,968	4.8	9.4	649,478	5.6	87.5
Unknown	18,439	2.2	8.5	26,473	1.8	12.2	172,478	1.5	79.3
Pregnancy hypertension^b
No	772,950	92.6	6.1	1310453	89.9	10.3	10655713	91.6	83.6
Yes	43,081	5.2	4.5	120437	8.3	12.5	802942	6.8	83.1
Unknown	18,439	2.2	8.5	26473	1.8	12.2	172478	1.5	79.3
Chronic hypertension^b
No	786,404	94.2	6.0	1364,227	93.6	10.3	11,045,265	95	83.7
Yes	29,627	3.5	5.8	66,663	4.6	13.1	413,390	3.6	81.1
Unknown	18,439	2.2	8.5	26,473	1.8	12.2	172,478	1.5	79.3
Eclampsia^b
No	806,516	96.7	5.9	1406,943	96.5	10.4	11,356,058	97.6	83.7
Yes	9515	1.1	7.0	23,947	1.6	17.6	102,597	0.9	75.4
Unknown	18,439	2.2	8.5	26,473	1.8	12.2	172,478	1.5	79.3

All values are significant with a p value of <0.001. Incidence rates are represented per 1000 all births.

^aData availability years: 1971–2018.

^bData availability years: 1989–2018.