The goal of this clinical trial is to evaluate the effect of laser assisted hatching (LAH) on pregnancy outcomes, with live birth rate as the primary outcome, in advanced age infertile women aged ≥35 years who are undergoing non-donor IVF/ICSI cycles and planning vitrified-warmed embryo transfer. It also aims to monitor the safety of LAH and assess various secondary pregnancy and neonatal outcomes. The main questions it aims to answer are:

Does laser assisted hatching improve the live birth rate in advanced age women undergoing vitrified-warmed embryo transfer? Does laser assisted hatching affect secondary outcomes including implantation rate, biochemical pregnancy rate, clinical pregnancy rate, ectopic pregnancy rate, ongoing pregnancy rate, miscarriage rate, multiple pregnancy rate, preterm birth rate, and rates of obstetric and neonatal complications as well as congenital anomalies? Researchers will compare the Laser Assisted Hatching (LAH) Group to the Control Group (without LAH) to see if LAH can improve pregnancy outcomes in the study population.

Participants will:

• Be randomly assigned to either the LAH Group or the Control Group at a 1:1 ratio, stratified by age (<40 years/≥40 years) and embryo stage (cleavage stage/blastocyst) using stratified block randomization.
• Undergo the first or second frozen-thawed embryo transfer cycle, with transferred embryos meeting the quality criteria (cleavage-stage embryos: Grade I, Grade II, or CP and above; blastocysts: 4BC/CB and above).
• Receive embryo vitrification and warming after routine fertilization and culture; LAH Group will undergo LAH (thinning zona pellucida for cleavage-stage embryos, removing 1/4-1/3 of zona pellucida circumference for blastocysts) in G2 medium after embryo thawing, while Control Group will not receive assisted hatching.
• Have endometrial preparation by natural, ovulatory, or hormone replacement cycles as appropriate, and 1-2 viable embryos will be transferred under ultrasound guidance within 3 hours after thawing, followed by routine luteal support after transfer.
• Complete follow-up at multiple time points: 12-15 days after embryo transfer (serum β-hCG test), 28 days after embryo transfer (transvaginal ultrasound), 12 weeks of gestation (ultrasound), 28 weeks of gestation (ultrasound), and 1 month after delivery (collection of delivery and neonatal information).
• Provide demographic, clinical, and embryological baseline data, as well as various outcome data during the study period.
• Undergo regular monitoring of vital signs, laboratory test results, and adverse events, with key prevention and control of specific risks related to LAH such as embryo damage and multiple pregnancy.

Inclusion Criteria:

• 1: Female age ≥ 35 years
• 2: First or second vitrified-warmed embryo transfer cycle
• 3: Quality of embryos for transfer meeting the criteria: Grade I, II, CP or above (cleavage-stage embryos); Grade 4BC/CB or above (blastocysts)
• 4: Provide written informed consent

Exclusion Criteria:

• 1: Use of donor oocytes or sperm, or planned preimplantation genetic testing (PGT)
• 2: Severe immune or chromosomal abnormalities
• 3: Uterine cavity abnormalities (i.e., adenomyosis, submucous uterine fibroids, hydrosalpinx, uterine septum, and endometrial polyps)
• 4: Embryos with an abnormal zona pellucida
• 5: Complicated with severe underlying diseases (e.g., uncontrolled hypertension/diabetes mellitus, active malignant tumors)
• 6: A history of recurrent implantation failure (≥2 cycles) or recurrent miscarriage (≥2 episodes)

De-identified individual participant data (IPD), along with the study protocol and statistical analysis plan, will be made publicly available via the National Clinical Research Data Sharing Platform (https://www.ncmc-data.org) within 12 months after study completion. The data will be accessible to qualified researchers in compliance with relevant laws, regulations, and ethical requirements.