Table 3.

Stratified analysis by socioeconomic status (SES) of the mother with logistic regression models with difference-in-differences analyses of the effect of the urban perinatal health programme on perinatal mortality, preterm birth and small-for-gestational age (SGA)

Lowest quintile household income	Perinatal mortality		Preterm birth		SGA
Independent variables	OR	95% CI	OR	95% CI	OR	95% CI
Trend per year	0.9516	0.9380 to 0.9654	1.0008	0.9958 to 1.0059	0.9864	0.9825 to 0.9903
Difference intervention and control group	0.8209	0.6786 to 0.9929	1.1677	1.0957 to 1.2444	1.1296	1.0749 to 1.1871
Programme effect (change in trend per year from 2010 onwards)	1.0673	0.9761 to 1.1670	0.9767	0.9481 to 1.0062	0.9947	0.9718 to 1.0181
Ethnicity non-Dutch	1.3668	1.5181 to 1.2307	0.8716	0.9024 to 0.8418	1.0167	1.0450 to 0.9893
Parity 0 (reference)	1.0000		1.0000		1.0000
Parity 1–2	0.7392	0.6652 to 0.8214	0.7826	0.7545 to 0.8117	0.6258	0.6084 to 0.6438
Parity 3	1.0544	0.8960 to 1.2407	1.0134	0.9539 to 1.0766	0.5605	0.5308 to 0.5918
Age <25 (reference)	1.0000		1.0000		1.0000
Age 25–34	1.0666	0.9478 to 1.2004	0.9566	0.9188 to 0.9960	0.8914	0.8647 to 0.9190
Age≥35	1.2893	1.1082 to 1.4999	1.1172	1.0597 to 1.1778	0.9334	0.8947 to 0.9737
Baseline rate*	11.2	9.8 to 12.7	70	67 to 74	181	175 to 188

Household income above 20th percentile	Perinatal mortality		Preterm birth		SGA
Independent variables	OR	95% CI	OR	95% CI	OR	95% CI
Trend per year	0.9402	0.9308 to 0.9497	0.9961	0.9930 to 0.9992	0.9787	0.9761 to 0.9813
Difference intervention and control group	0.9084	0.7553 to 1.0926	1.0472	0.9884 to 1.1094	1.1500	1.0978 to 1.2046
Intervention effect (change in trend per year from 2010 onwards)	1.0294	0.9403 to 1.1270	0.9841	0.9585 to 1.0103	0.9876	0.9663 to 1.0093
Ethnicity non-Dutch	1.2108	1.3017 to 1.1262	1.0665	1.0913 to 1.0423	1.4399	1.4678 to 1.4126
Parity 0 (reference)	1.0000		1.0000		1.0000
Parity 1–2	0.7592	0.7057 to 0.8166	0.5592	0.5467 to 0.5721	0.4956	0.4859 to 0.5056
Parity 3+	1.4987	1.3058 to 1.7201	0.7298	0.6905 to 0.7713	0.4446	0.4206 to 0.4700
Age <25 (reference)	1.0000		1.0000		1.0000
Age 25–34	0.8417	0.7489 to 0.9461	0.9544	0.9206 to 0.9894	0.8185	0.7950 to 0.8427
Age≥35	1.1253	0.9880 to 1.2816	1.0446	1.0024 to 1.0886	0.9142	0.8835 to 0.9459
Baseline rate*	9.2	8.1 to 10.4	80	76 to 83	179	173 to 185

Perinatal mortality is defined as stillbirth from 24 weeks onwards plus early neonatal mortality. The total number of observations for the perinatal mortality model is 238 226 for low SES and 704 388 for high SES. Preterm is defined as born before a gestational age of 37 weeks and SGA is defined as a birth weight below the 10th percentile corrected for gestational age and sex. The total number of observations for the preterm birth and SGA models is 236 737 for low SES and 701 524 for high SES. Low SES was defined as the lowest 20 percentile by disposable household income per year.

*For perinatal mortality per 1000 live and stillbirths, for preterm birth and SGA per 1000 live births.