Table 2 Demographic and birth characteristics of the study population according to the mode of delivery.

	Levels	Vaginal birth	Caesarean section	P value
n		575	57
Age (years)		20.6 ± 0.5	20.5 ± 0.5	0.82
Sex	Males	256 (44.5%)	35 (61.4%)	0.018
Sex	Females	319 (55.5%)	22 (38.6%)
Birth weight (g)		2983 ± 425	2939 ± 513	0.46
Birth weight z-score		− 0.52 ± 0.91	− 0.67 ± 1.10	0.27
Gestational age (weeks)		39.2 ± 1.6	39.3 ± 2.2	0.70
Maternal age at childbirth (years)		26.2 ± 4.6	26.9 ± 4.5	0.28
Maternal BMI (kg/m²)^a		21.31 ± 2.47	21.65 ± 2.96	0.33
Maternal PIH^b		22 (3.8%)	3 (5.3%)	0.49
Maternal smoking at pregnancy		4 (0.7%)	1 (1.8%)	0.38
Maternal alcohol consumption during pregnancy		6 (1.0%)	1 (1.8%)	0.49
Maternal education^c	Less than high school	405 (81.5%)	37 (78.7%)	0.79
Maternal education^c	High school or greater	92 (18.5%)	10 (21.3%)
Paternal education	Less than high school	351 (70.6%)	33 (70.2%)	0.85
Paternal education	High school or greater	146 (29.4%)	14 (29.8%)
Offspring education	High school or lesser	81 (18.2%)	8 (17.8%)	> 0.99
Offspring education	University	363 (81.8%)	37 (82.2%)
Family income (baht per month)^d		2500 [1500, 4000]	3200 [1800, 5000]	0.10
Offspring current smoking		63 (10.9%)	10 (17.5%)	0.31

Continuous data are means ± SD or median [quartile 1, quartile 3], as appropriate; categorical data are n (%).
BMI body mass index, PIH pregnancy-induced hypertension.
P values that are statistically significant (at p < 0.05) are shown in bold.
^aBMI recorded at the first antenatal visit in the original study in 1989–1990.
^bPIH was defined as a systolic blood pressure ≥ 140 mmHg and/or diastolic blood pressure ≥ 90 mmHg developed after 20 weeks of gestation without proteinuria, in a previously normotensive woman.
^cThere were missing data on the highest level of education, so that the available sample sizes for the vaginal birth and caesarean section groups, respectively, were: maternal education [497 (86.4%) and 47 (82.5%)], paternal education [49 (86.4%) and 47 (82.5%)], and offspring education [444 (77.2%) and 45 (78.9%)].
^dIncome recorded at the time of maternal recruitment to the original study in 1989–1990 (i.e., not adjusted for inflation); the available sample sizes were 495 (86.1%) for the vaginal birth group and 47 (82.5%) for the caesarean section group.

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