The purpose of this study is to assess the efficacy of LMWH treatment in women with unexplained infertility and negative immunological markers undergoing ICSI.

Inclusion criteria:

1. patients undergoing 1st trial ICSI
2. unexplained infertility
3. negative immunological markers including ACL abs, LAC, ANA, ATA, AnitdsDNA

Exclusion criteria:

1. previous IVF/ICSI
2. Any cause of infertility
3. Suspected and/or unexpected poor response during ovulation induction
4. positive immunological markers
5. Age > 40 years.

All participants will undergo IVF/ICSI cycle using the Long luteal phase protocol. the dose of gonadotropins will be calculated according to patient age and BMI. All patients will have 2-3 embryos transferred at D5 according to their age. the primary outcome will be LBR. secondary outcomes will include biochemical pregnancy rate and clinical pregnancy rate.

Inclusion Criteria:

• age less than 38 years
• at least 12 months of infertility
• women with unexplained infertility

Exclusion Criteria:

• age more than or equals 38 years
• serum AMH level less than or equals 1 ng/ml
• patients of anticoagulant therapy
• immune-compromised patients
• patients with contraindications to low molecular weight heparin
• positive immunological markers
• patients with other than unexplained infertility
• male factor infertility
• refusal of participation
• patients with unexpected poor or over response during induction of ovulation