Revisiting the association between maternal and offspring preterm birth using a sibling design

Table 4 Association between maternal and offspring preterm birth type in the sibling subcohort^a, Manitoba, Canada, 1980–2016

		Infant’s PTB cases/No of births	PTB rate, %	(N = 2494)		(N = 2494)		(N = 2157)		(N = 1031)
Offspring outcome	Maternal PTB type	Infant’s PTB cases/No of births	PTB rate, %	URR	95% CI	ARR^b	95% CI	ARR^c	95% CI	ARR ^d	95% CI
Any PTB	Not Preterm	143/1425	10.04	1.00	Reference	1.00	Reference	1.00	Reference	1.00	Reference
	Spontaneous	72/611	11.78	1.17	0.85, 1.63	1.18	0.86, 1.63	1.16	0.82, 1.61	1.01	0.64, 1.59
	Provider-initiated	37/458	8.08	0.81	0.54, 1.21	0.80	0.54, 1.17	0.64	0.40, 1.05	0.68	0.38, 1.24
Spontaneous PTB	Not Preterm	90/1425	6.32	1.00	Reference	1.00	Reference	1.00	Reference	1.00	Reference
	Spontaneous	52/611	8.51	1.35	0.97, 1.87	1.39	0.99, 1.93	1.37	0.91, 2.07	1.26	0.73, 2.20
	Provider-initiated	23/458	5.02	0.80	0.51, 1.24	0.78	0.50, 1.20	0.79	0.45, 1.40	0.85	0.42, 1.74
Provider-initiated PTB	Not Preterm	53/1425	3.72	1.00	Reference	1.00	Reference	1.00	Reference	1.00	Reference
	Spontaneous	20/611	3.27	0.88	0.51, 1.51	0.87	0.50, 1.52	0.83	0.49, 1.44	0.65	0.29, 1.46
	Provider-initiated	14/458	3.06	0.82	0.44, 1.54	0.80	0.43, 1.50	e		e

Abbreviations: PTB preterm birth, URR Unadjusted Relative Risk, ARR Adjusted Relative Risk, CI confidence intervals
^aAnalyzed with a generalized estimating equations fixed-effects log-binomial regression model. 5 children excluded due to missing information on maternal preterm type
^bAdjusted for whether mother moved or had a substance abuse diagnosis in year before birth of child, child’s birth year, mother’s age at birth of child, neighborhood location and SES at birth of child, child’s sex and child’s birth order
^cRestricted to births 2000–2016 with complete information on additional covariates. Adjusted for whether mother moved or had a substance abuse diagnosis in year before birth of child, child’s birth year, mother’s age at birth of child, neighborhood location and SES at birth of child, child’s sex, child’s birth order, mother’s smoking status during pregnancy, mother’s education, inadequate prenatal care, receipt of employment income assistance in the year before the birth of the child, and whether mother had a partner
^dRestricted to one randomly birth per mother (1995–2016). Adjusted for whether mother moved or had a substance abuse diagnosis in year before birth of child, child’s birth year, mother’s age at birth of child, neighborhood location and SES at birth of child, child’s sex and child’s birth order
^eSuppressed due to small number of events (≤6)

ISSN: 1471-2393