This will be a prospective, randomized (1:1 ratio) clinical trial for patients with severe male-factor infertility with or without preimplantation genetic screening (PGS). Qualified 450 patients are randomized into either of two groups: group A will undergo intracytoplasmic sperm injection (ICSI) without PGS (225 cases), Group B will undergo ICSI with PGS (225 cases). The partners of all participants will receive the same protocol for ovarian stimulation and standardized luteal phase support.

The target population will be patients with severe male-factor infertility aged between 20 and 55 years, diagnosed by the ESHER Criteria (Non-obstructive oligospermia，asthenspermia). Women with other reasons of infertility (eg. advanced age, anovulation, endometriosis, and premature ovarian failure) are excluded.

The randomization will take place 3-6 days after the oocyte pick-up day by a computer randomization system. The pregnancy test results, pregnancy complications, congenital anomalies, neonatal complications will be followed up by checking medical records and telephone calls.

Inclusion criteria

1. Male partner age of 20-55 years old, Chinese.
2. Male partner has severe male infertility (defined as a semen concentrate less than 5×10^6/ml, and/or with a progressive motility less than 10%).
3. Proposed ICSI to assist pregnancy.
4. Fully explain the nature of the research and obtain the informed consent of the subject before carrying out any procedure in the research protocol. If a subject is not capable of expressing opinions, the legal representative of the subject can sign the informed consent on behalf of the subject.

Exclusion criteria

Any one of the following criteria should be excluded from this study:

1. Male partner had been diagnosed with obstructive azoospermia, sexual dysfunction, and immune infertility.
2. Female partner at 38 years of ages and older.
3. Female partner has uterine abnormalities such as uterine malformations (unicornuate uterus, mediastinal uterus, double uterus, double horn uterus, etc.), adenomyosis, submucosal fibroids or intrauterine adhesions.
4. Female partner has a history of recurrent abortion, including biochemical pregnancy (≥3 time miscarriages).
5. One of the couples has abnormal chromosomal karyotypes, excluding chromosomal polymorphisms.
6. Female partner has contraindications for assisted reproduction, such as poorly controlled type I or type II diabetes mellitus; undiagnosed liver disease or abnormal liver function (abnormal serum liver enzymes); kidney disease or abnormal kidney function; severe anemia; history of deep venous thrombosis; history of pulmonary embolism; history of cerebrovascular accident; poorly controlled hypertension or diagnosed heart disease; history of cervical cancer, endometrial cancer or breast cancer; unexplained vaginal bleeding.
7. Male partner has contraindications for assisted reproduction, such as poorly controlled type I or type II diabetes mellitus; undiagnosed liver disease or abnormal liver function (abnormal serum liver enzymes); kidney disease or abnormal kidney function; severe anemia; history of deep venous thrombosis; history of pulmonary embolism; history of cerebrovascular accident; poorly controlled hypertension or diagnosed heart disease.
8. One of the couple refuses to cooperate with the study.
9. Patients who have been included in the experimental group or control group of this study.