A parsimonious explanation for intersecting perinatal mortality curves: understanding the effects of race and of maternal smoking

Table 3 Gestational Age-Specific Birth, Growth-Restriction and Perinatal Mortality Rates, Nonsmokers, United States, 1997.

Gestational age	Live births	SGA live births	Stillbirths	Neonatal deaths	Fetuses at risk	Birth rate	Growth-restriction rate (1)*	Growth-restriction rate (2)*	Perinatal mortality rate (1)*	Perinatal mortality rate (2)*
32	11,972	1,231	381	161	2,454,357	5.0	10.3	0.5	41.3	0.21
33	17,679	2,014	389	179	2,442,004	7.4	11.4	0.8	29.0	0.21
34	30,271	3,304	465	219	2,423,936	12.7	10.9	1.4	21.0	0.27
35	51,988	5,143	495	239	2,393,200	21.9	9.9	2.2	12.9	0.28
36	94,656	8,913	533	278	2,340,717	40.7	9.4	3.9	7.6	0.31
37	188,867	16,313	569	368	2,245,528	84.4	8.6	7.4	4.4	0.37
38	392,302	30,727	599	458	2,056,092	191.1	7.8	15.1	2.2	0.43
39	601,401	48,429	624	553	1,663,191	362.0	8.1	29.6	1.6	0.58
40	569,467	44,473	482	460	1,061,166	537.1	7.8	42.9	1.3	0.70
41	299,521	20,433	261	255	491,217	610.3	6.8	43.8	1.4	0.82
≥42†	191,199	8,325	236	216	191,435	1,000.0	8.6	49.7	1.9	1.91
Total ‡	2,491,884	198,876	8,976	6,878	2,500,860	1,000.0	8.1	80.9	5.6	5.55

* Total births and live births at each gestational week served as the denominators for perinatal mortality rates (1) and growth-restriction rates (1), respectively. Perinatal mortality and growth-restriction rates (2) were calculated using the number of fetuses at risk as the denominator (see text). Fetuses-at-risk for the growth-restriction rate calculation exclude those over 44 weeks and those with missing gestational age or birth weight. All rates are expressed per 1,000 except for growth-restriction rates (1) which are per 100. † This period of risk exceeds 1 week and partly explains the large increase in the perinatal mortality rate (2). ‡ All gestational ages, including those <32 weeks and those with missing gestational age. SGA denotes small for gestational age.

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