There are many causes of fetal abortion. Generally, we will check anti-cardiolipin antibodies, D-dimer, NK killer cells, confinement antibodies, β2 glycoprotein antibodies, lupus anticoagulant, platelet coagulation test, thyroid function, basal hormone levels, follicular development, preovulatory endometrial condition and hormones (estrogen, progesterone, luteinizing hormone) on the third and fifth day after ovulation, peripheral blood chromosomes of both partners, male semen routine, sperm chromatin diffusion test, etc. For special patients, we will measure the three-dimensional ultrasound on the seventh day after ovulation to see the uterine artery blood flow and endometrial volume.