Children and Maternal Characteristics
From 2004 through 2011, 1,603,794 infants were born. A total of 1,494,843 singleton live births were included after excluding stillbirths, non-singleton births, children with missing maternal ID numbers, premature newborns with a gestational age less than 24 weeks, implausible combinations of birth weight and gestational age, children of mothers from developed countries, and children with missing data on residence area. There were 682,982 (45.7%) singleton live births to urban TBMs, 662,818 (44.3%) to rural TBMs, 61,570 (4.1%) to urban FBMs, and 87,473 (5.9%) to rural FBMs. Regarding to nationality of FBMs, mainland China (52.94%) was the predominant country, followed by Vietnam (33.01%), Indonesia (7.29%), Philippines (2.24%), Thailand (1.94%), Cambodia (1.31%), Myanmar (1.28%) (Fig.1).
The annual numbers of births from 2004 through 2011 declined in all 4 maternal groups, except for the sudden drop in 2010 which is Tiger year, a Chinese zodiac. In Chinese belief, people born in Tiger year tend to have an unlucky life. 19 The male:female ratio of 52:48 remained constant among the 4 maternal groups. The mean birth weight was lowest for rural TBMs, followed by urban TBMs, rural FBMs, and urban FBMs. The rate of low birth weight (<2500g), preterm rate (<37 weeks) and percentage of SGA children was highest for rural TBMs, followed by urban TBMs, rural FBMs, and urban FBMs (Table 1).
Maternal age at delivery was mean age of 26.69 years for rural FBMs, 27.48 years for urban FBMs, 28.96 years for rural TBMs, and 30.79 years for urban TBMs. About 24.2% of TBMs were unemployed, whereas 82.1% of FBMs were unemployed. Similarly, most FBMs had an income less than p20 (NT$15840 per month) (Table 1).
Incidence Rates of 18 Severe Diseases
Fig. 2 ranks the incidence rates of 18 severe diseases for the 4 maternal groups. Congenital circulatory anomalies had the highest incidence rate, followed by all-cause mortality, psychoses with origin specific to childhood, congenital cleft palate and cleft lip, infantile cerebral palsy, vasculitis (in children, almost all Kawasaki disease), chromosomal anomalies, other congenital anomalies of the digestive system, congenital anomalies of the urinary system, long-term mechanical ventilation, type I diabetes mellitus, congenital hypothyroidism, major trauma/burn, lymphoid leukemia, congenital nervous anomalies, other and unspecified congenital anomalies, malignant neoplasm of the brain, and disorders of amino-acid transport and metabolism. The incidence rates of 8 severe diseases significantly differed among the 4 maternal groups, namely, congenital circulatory anomalies (p=.0002), all-cause mortality (p<.0001), psychoses (p<.0001), infantile cerebral palsy (p=.0081), vasculitis, including Kawasaki disease (p<.0001), congenital hypothyroidism (p=.0341), major trauma/burn (p<.0001), and congenital nervous anomalies (p=.0011). The category other and unspecified congenital anomalies was statistically significant (p=.0412) but was not considered because such events were combined from several congenital anomalies.
Adjusted Hazard Ratios for 8 Severe Diseases
Fig. 3 shows age-specific cumulative incidence rates and adjusted hazard ratios (HRs) for 8 severe diseases among children in the 4 maternal groups. Four major patterns were observed, as detailed below.
(1) The incidence of vasculitis differed between FBMs and TBMs: the cumulative incidence rate was higher for children of TBMs than for children of FBMs (Fig. 3f). The adjusted HR for FBMs, as compared with TBMs, was 0.63 (95% CI, 0.50-0.78).
(2) Incidence rates for several conditions differed between urban and rural mothers, namely, congenital hypothyroidism (Fig. 3c), psychoses (Fig. 3e), major trauma/burn (Fig. 3g), and all-cause mortality (Fig. 3h). Rates of congenital hypothyroidism and psychoses were higher among urban children than among rural children. As compared with urban children, rural children had adjusted HRs of 0.80 (95% CI, 0.67-0.94) for congenital hypothyroidism and 0.64 (95% CI, 0.58-0.70) for psychoses. In contrast, rates of major trauma/burn and all-cause mortality were higher in rural areas than in urban areas. In rural areas, the adjusted HRs were 1.59 (95% CI, 1.33-1.90) for major trauma/burn and 1.28 (95% CI, 1.18-1.38) for all-cause mortality, as compared with urban areas.
(3) Rates of congenital circulatory anomalies (Fig. 3a) and infant cerebral palsy (Fig. 3b) were highest among the children of rural TBMs. As compared with rural TBMs, the adjusted HR for congenital circulatory anomalies was 0.93 (95% CI, 0.89-0.97) for urban TBMs, 0.91 (95% CI, 0.81-1.02) for urban FBMs, and 0.90 (95% CI, 0.81-0.99) for rural FBMs. As compared with rural TBMs, the adjusted HR for infant cerebral palsy was 0.87 (95% CI, 0.78-0.97) for urban TBMs, 0.72 (95% CI, 0.53-0.97) for urban FBMs, and 0.92 (95% CI, 0.74-1.15) for rural FBMs.
(4) Incidence rates did not greatly differ between the children of FBMs and TBMs, but there was a variable urban—rural difference in congenital anomalies of the nervous system (Fig. 3d). Although children of urban FBMs had a higher cumulative incidence rate of congenital nervous anomalies than did children of urban TBMs, the relationship reversed among children of rural mothers.
Incidence rates varied with age (Fig. 3). The cumulative incidence rates of congenital circulatory anomalies, congenital hypothyroidism, and congenital nervous anomalies increased quickly until age 1 year and increased more slowly until age 5 years. The cumulative incidences of infantile cerebral palsy and vasculitis rapidly increased until age 5 years and remained relatively constant thereafter. No child developed psychosis before age 2 years, but rates rose sharply, and differed in relation to urbanicity, after that. Incidence rates for major trauma/burn and all-cause mortality exhibited a similar pattern, except that rates rose slowly after age 18 months.