Etiological screening investigation
All the patients were also recommended to investigate some presumptive causes of abortion beside chromosome analysis, such as Mycoplasma and Chlamydia infection, B mode ultrasound for uterine anatomical structure (including saddle uterus, mediastinal uterus, unicornuate uterus, naive uterus and intrauterine adhesions, endometrial polyps, uterine fibroids, adenomyosis), flow cytometry for peripheral blood lymphocyte subsets including natural killer cellsets and regulatory T cell (BD, Franklin Lakes, New Jersey, USA), ovarian hormone, thyroid hormone, and prolactin, folic acid and vitamin B12 (Roche Company, Basel, Switzerland), anti-phospholipid antibodies including anti-cardiolipin, anti-β2-glycoprotein, anti-phosphatidylserine/ ethanolamine (EUROIMMUN, Lubeck, German) and connective tissue antibodies including anti-dsDNA, Nucleosomes, Histones, SmD1, PCNA, Rib Po, SSA/Ro 60Kd, SSA/Ro 52Kd, SS-B/La, CENP-B, Scl 70, U1-snRNP, AMA M2, Jo-1, Pm-Sc1, Mi-2, Ku, and ANA (EUROIMMUN, Lubeck, German). All the patients were treated similarly according to their abnormal results except chromosomal problems.