Preterm birth and single nucleotide polymorphisms in cytokine genes

Preterm birth (PTB) is defined as any birth before 37 weeks of gestation, or less than 259 days of pregnancy, beginning the first day of a last menstrual period (1). Term birth is defined as a delivery no sooner than 37 weeks. PTB is one of the most complicated problems that contribute to prenatal morbidity and mortality, responsible for 75% of infant deaths and 62% of early neonatal deaths among pregnancies in six developing countries (2), and the rate of PTB is increasing every year. Worldwide, 7.8% of 14.9 million annual PTBs occur in China; this ranks second to India, which has the highest prevalence of PTB (3)