Factors associated with preterm birth: from logistic regression to structural equation modeling

Oliveira, Adelaide Alves de; Almeida, Marcia Furquim de; Silva, Zilda Pereira da; Assunção, Paula Lisiane de; Silva, Ana Maria Rigo; Santos, Hellen Geremias dos; Alencar, Gizelton Pereira

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METHODOLOGICAL ISSUES • Cad. Saúde Pública 35 (1) • 2019 • https://doi.org/10.1590/0102-311X00211917 copy

Factors associated with preterm birth: from logistic regression to structural equation modeling

Authorship SCIMAGO INSTITUTIONS RANKINGS

This study proposed the application of structural equation modeling (SEM) to investigate variables associated with preterm birth based on a theoretical model analyzed previously by hierarchical logistic regression. The data came from a population-based case-control observational study of hospital births to mothers residing in Londrina, Paraná State, Brazil (June 2006 to March 2007). For the SEM, the study considered the association between socioeconomic characteristics and psychosocial aspects pertaining to reproductive history, work and physical activity, complications during the pregnancy, and fetal characteristics. It also considered the relationship between these associations and the outcome preterm birth mediated by adequacy of prenatal care. The weighted least square mean and variance adjusted estimator (WLSMV) was used for categorical data and robust maximum likelihood (MLR) for odds ratios. Three latent variables were created: socioeconomic vulnerability, family vulnerability, and unwanted pregnancy. The effect of socioeconomic and family vulnerability and unwanted pregnancy on prematurity occurred indirectly through inadequacy of prenatal care. The proposed methodology allowed using constructs, verifying the role of mediation by inadequacy of prenatal care, and identifying the variables’ direct and indirect effects on the outcome preterm birth.

Keywords:
Statistical Models; Logistic Models; Risk Factors; Premature Birth

Variables	Factor 1	Factor 2
Low head-of-household’s schooling (≤ 8 years)	0.987	-0.019
Low maternal schooling (≤ 8 years)	0.795	-0.022
Per capita income (minimum wage)	-0.790	-0.088
Number of persons per room	0.735	0.056
Type of dwelling (slum)	0.648	0.011
Non-nuclear family	0.158	0.930
Household headed by the mother	-0.069	0.812
Presence of elderly	0.005	0.792
Mother lives with husband/partner less than 2 years	-0.103	0.692

Variables	Factor 1
Planned pregnancy	0.911
Mother’s negative reaction or worries with the pregnancy	0.969
Father’s negative reaction or worries with the pregnancy	0.774
Family’s negative reaction or worries with the pregnancy	0628

Variables	Cases		Controls		Total
Variables	n	%	n	%	n	%
Maternal reproductive history
a) One or more pregnancies, no previous premature birth, and age 20 to 34 years	86	29.1	129	39.2	215	34.4
b) Nulliparous, age 13 to 19 years	35	11.8	44	13.4	79	12.6
c) One or more pregnancies, no previous premature birth, and age 35 years or older	22	7.4	38	11.6	60	9.6
d) Nulliparous, age 20 to 34 years	76	25.7	83	25.2	159	25.4
e) One or more pregnancies, no previous premature birth, no previous low birth weight, age 13 to 19 years	11	3.7	10	3.0	21	3.4
f) Nulliparous, age 35 years or older	9	3.0	2	0.6	11	1.8
g) One or more pregnancies, previous premature birth, previous low birth weight	57	19.3	23	7.0	80	12.8
Mother’s behavioral activities: physical effort
a) Mother does not work away from home, no strenuous housework	77	26.0	77	23.4	154	24.6
b) Mother does not work away from home, does strenuous housework	55	18.6	57	17.3	112	17.9
c) Mother works away from home without physical effort, no strenuous housework	94	31.8	92	28.0	186	29.8
d) Mother works away from home with physical effort, no strenuous housework	15	5.1	22	6.7	37	5.9
e) Mother works away from home without physical effort, does strenuous housework	28	9.5	47	14.3	75	12.0
f) Mother works away from home with physical effort, does strenuous housework	27	9.1	34	10.3	61	9.8

Variables and factors’ indicators	WLSMV				MLR
Variables and factors’ indicators	Standardized estimate	Estimate	SE	p-value	Estimate	SE	p-value	OR
Measurement model
SEV
Persons per room	0.652	1.000	0.000	-	1.000	0.000	-	-
Per capita income	-0.877	-2.483	0.134	0.000	-2.412	0.170	0.000	-
Mother’s schooling	0.841	4.798	0.476	0.000	7.274	0.843	0.000	-
Father’s schooling	0.741	3.403	0.286	0.000	5.872	0.744	0.000	-
Type of dwelling	0.661	2.716	0.427	0.000	5.875	0.924	0.000	-
FV
Living with husband/partner less than 2 years	0.669	1.000	0.000	-	1.000		0.000	-	-
Non-nuclear family	0.994	9.722	30.591	0.751	2.877		1.204	0.017	-
Presence of elderly	0.768	1.332	0.256	0.000	1.812		0.414	0.000	-
Relationship mother/guardian	0.776	1.367	0.218	0.000	1.503		0.245	0.000	-
UP
Mother’s reaction when learned of pregnancy	0.785	1.000	0.000	-	1.000		0.000	-	-
Father’s reaction when learned of pregnancy	0.825	1.150	0.302	0.000	1.239		0.278	0.000	-
Family’s reaction when learned of pregnancy	0.825	1.150	0.272	0.000	1.003		0.253	0.000	-
Structural model
UP =
FV	0.365	0.515	0.129	0.000	0.561		0.133	0.000	-
SEV	0.267	1.043	0.241	0.000	2.225		0.524	0.000	-
Mother’s reproductive history	0.025	0.016	0.032	0.616	0.055		0.058	0.343	-
Alcohol consumption in pregnancy	0.166	0.983	0.368	0.007	1.265		0.590	0.032	-
Complications =
Mother’s reproductive history l	0.039	0.021	0.028	0.454	0.052		0.042	0.215	1.053
Physical effort	0.067	0.044	0.034	0.203	0.046		0.053	0.380	1.047
Walks	-0.020	-0.047	0.133	0.726	-0.267		0.199	0.179	0.765
BMI	0.099	0.155	0.076	0.041	0.295		0.127	0.021	1.343
Alcohol consumption in pregnancy	0.041	0.198	0.222	0.372	0.439		0.411	0.285	1.552
Multiple pregnancy	0.224	0.972	0.228	0.000	1.621		0.392	0.000	5.057
Worries	0.107	0.253	0.117	0.031	0.426		0.191	0.026	1.531
Inadequate prenatal care I =
SEV	0.091	0.323	0.219	0.140	0.713		0.384	0.063	2.041
FV	0.088	0.112	0.099	0.256	0.163		0.116	0.160	1.177
UP	0.347	0.314	0.094	0.001	0.199		0.093	0.032	1.221
Mother’s reproductive history	0.149	0.086	0.030	0.005	0.100		0.046	0.028	1.106
Physical effort	-0.092	-0.066	0.038	0.082	-0.050		0.060	0.399	0.951
Inadequate prenatal care II =
SEV	0.096	0.367	0.395	0.353	1.258		0.878	0.152	3.519
FV	-0.006	-0.008	0.175	0.963	0.105		0.200	0.601	1.110
UP	0.467	0.457	0.169	0.007	0.326		0.174	0.061	1.385
Mother’s reproductive history	0.188	0.118	0.046	0.001	0.127		0.083	0.127	1.158
Physical effort	-0.159	-0.124	0.059	0.034	-0.154		0.130	0.237	0.857
Gestational age =
SEV	-0.083	-0.551	0.611	0.367	0.007		0.383	0.986	1.007
FV	0.073	0.175	0.233	0.452	0.022		0.102	0.827	1.023
UP	-0.420	-0.714	0.462	0.122	-0.045		0.076	0.556	0.956
Mother’s reproductive history	0.091	0.098	0.072	0.172	0.213		0.047	0.000	1.237
Inadequate prenatal care I	0.226	0.426	0.227	0.051	0.457		0.224	0.041	1.579
Inadequate prenatal care II	0.555	0.965	0.539	0.044	1.457		0.500	0.004	4.293
Complications	0.584	1.209	0.489	0.013	1.825		0.204	0.000	6.201
Multiple pregnancy	0.214	1.924	0.739	0.009	2.876		0.773	0.000	17.747
Physical effort	-0.034	-0.046	0.090	0.612	-0.146		0.064	0.023	0.864
Worries	0.040	0.198	0.227	0.384	0.424		0.218	0.052	1.527
Walks	-0.133	-0.641	0.300	0.032	-0.606		0.235	0.010	0.545
BMI	0.146	0.473	0.188	0.012	0.449		0.157	0.004	1.567
Alcohol consumption in pregnancy	0.114	1.147	0.555	0.039	1.131		0.393	0.004	3.099
Correlations
FV with mother’s reproductive history	0.065	0.116	0.096	0.225	0.226		0.148	0.127	-
SEV with mother’s reproductive history	0.170	0.109	0.022	0.000	0.100		0.030	0.001	-
SEV with physical effort	-0.181	-0.093	0.022	0.000	-0.096		0.021	0.000	-
SEV with FV	0.175	0.051	0.016	0.001	0.079		0.027	0.003	-
SEV with BMI	0.147	0.032	0.009	0.001	0.025		0.010	0.014	-
SEV with walks	-0.228	-0.033	0.015	0.033	-0.033		0.007	0.000	-
BMI with walks	-0.043	-0.013	0.013	0.345	-0.011		0.011	0.024	-
Intercepts
Persons per room	1.456	0.724	0.154	0.000	0.852		0.020	0.000	-
Per capita income	0.093	0.085	0.217	0.693	0.037		0.037	0.931	-

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[1] Correspondence G. P. Alencar Faculdade de Saúde Pública, Universidade de São Paulo. Av. Dr. Arnaldo 715, São Paulo, SP 01246-904, Brasil. gizelton@usp.br