The Hokkaido Birth Cohort Study on Environment and Children’s Health: cohort profile—updated 2017

Table 5 Outcomes of singleton fetuses (n = 18,882) at birth in the Hokkaido cohort

Outcomes	Number	Percent	95% CI
Miscarriage^a	200	1.1	0.9–1.2
Artificial abortion^b	52	0.28	0.21–0.36
Stillbirth^c	60	0.32	0.24–0.41
Live birth	18,570	98.3	98.2–98.5
Preterm birth^d	923	4.9	4.6–5.2
Moderate preterm birth	795	4.2	3.9–4.5
Very preterm birth	112	0.59	0.49–0.71
Extremely preterm birth	47	0.24	0.18–0.33
Low birth weight^e	1693	9.0	8.6–9.4
Very low birth weight	268	1.4	1.2–1.6
Extremely low birth weight	204	1.1	0.9–1.2
Macrosomia^f	190	1.0	0.9–1.2
Small for gestational age^g	1308	7.0	6.7–7.4
Term small for gestational age^h	1211	6.5	6.2–6.9
Small for reference fetal weightⁱ	814	4.8	4.5–5.2

Missing data were excluded from the calculation
CI confidence interval
^aMiscarriage was defined as the loss of a pregnancy at <22 completed gestational weeks
^bAn abortion brought about intentionally at <22 completed gestational weeks
^cStillbirth was defined as the birth of a dead fetus at ≥22 completed gestational weeks
^dPreterm birth was defined as birth at 22–36 completed gestational weeks. Preterm birth was subdivided into three categories of prematurity: moderately preterm (32–36 completed weeks), very preterm (28–31 completed weeks), and extremely preterm (22–27 completed weeks)
^eLow birth weight, very low birth weight, and extremely low birth weight were birth weights <2500, <1500, and <1000 g, respectively
^fMacrosomia is birth weight ≥4000 g
^gSmall for gestational age infants had birth weights less than the 10th percentile of the reference birth weight estimated by using gestational age, sex, and parity
^hTerm small for gestational age infants were the small for gestational age infants among the term birth neonates
ⁱSmall for reference fetal weight infants had birth weights <1.5 standard deviations of the reference ultrasound-based fetal weight estimated from gestational age, sex, and parity

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