['The aim of this study was to explore the association of the DNA-methyltransferase (DNMT)-3A and DNMT3B promoter polymorphisms with the risk of human spontaneous abortion after assisted reproduction techniques (ARTs) and natural conception.', 'We collected tissues from women who underwent abortion procedures: (a) chorionic villus samples (CVS) and muscle samples (MS) from spontaneous abortions conceived by ART and natural cycle (study group), n\u2009=\u2009152; and (b) CVS and MS from normal early pregnancy and second trimester (control group), n\u2009=\u2009155. The single-nucleotide polymorphism (SNP) -448A\u2009>\u2009G in the DNMT3A promoter region and -149C/T polymorphism of DNMT3B were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and confirmed by sequencing.', 'The allele frequency of -448A among pregnancy loss group and control group was 34.2\xa0% vs. 16.5\xa0%, respectively. Compared with GG carriers, the DNMT3A -448AA homozygotes had an about 16-fold increased risk of spontaneous abortion [odds ratio (OR)\u2009=\u200916.130, 95\xa0% confidence interval (CI), 3.665-70.984], and AG heterozygotes had an OR of 2.027 (95\xa0% CI, 1.247-3.293). However, the distribution of -448A\u2009>\u2009G in individuals derived from ART pregnancies was not statistically significantly compared with those derived from spontaneous pregnancies (P\u2009=\u20090.661). For DNMT3B, we observed genotype frequencies of 100\xa0% (TT) in the study group and the control group.'] Is dNA methyltransferase 3A promoter polymorphism associated with the risk of human spontaneous abortion after assisted reproduction techniques and natural conception?