Criteria for the diagnosis of BDs and definitions of
parameters
BDs were diagnosed by obstetricians using ultrasonographic, genetic,
pathologic, clinical, and laboratory tests, on the basis of the
International Statistical Classification of Diseases and Related Health
Problems, 10th Revision (Q00–Q99).22 We studied 25
types of BD, including congenital heart defects (CHDs), congenital
malformation of the urinary system, cleft lip with cleft palate, cleft
lip without cleft palate, cleft palate without cleft lip, polydactyly,
syndactyly, congenital hydrocephalus, congenital talipes equinovarus,
congenital microtia, other malformation of the external ear, trisomy 21
syndrome, other chromosomal abnormalities, hypospadias, anencephaly,
spina bifida, encephalocele, omphalocele, limb reduction defect,
congenital atresia of the rectum and anus, congenital diaphragmatic
hernia, gastroschisis, congenital esophageal atresia, conjoined twins,
and exstrophy of the urinary bladder.
We categorized mothers according to their age (<20, 20–34,
and ≥35 years); whether they lived in a urban or rural environment;
whether their educational level was primary or below, middle or high
school, or college or above; parity (0, 1, or ≥2); whether their
offspring were male, female, or of unknown sex; and whether the BD of
their child was diagnosed prenatally or postnatally.