Background: Morphology-based embryo selection cannot detect aneuploidy, which is common in advanced maternal age and recurrent pregnancy loss. NICS-AI combines non-invasive chromosome screening (NICS) of cell-free DNA from spent blastocyst culture medium with AI integration of developmental day and morphology to improve embryo ranking.

Methods: This multicenter, single-blind, parallel randomized controlled trial will include 520 participants. Participants undergoing conventional IVF will be eligible if they meet either (i) female age 35-43 years or (ii) recurrent miscarriage (≥2 losses <28 gestational weeks, including biochemical pregnancy with serum hCG >25 IU/L). They must consent to blastocyst culture/vitrification and frozen-thawed single blastocyst transfer (SBT), and have ≥2 Day-5/Day-6, 2PN-derived blastocysts with morphology grade ≥4BC/4CB at randomization. Key exclusions include any ICSI-based fertilization or PGT-related procedures, known genetic disease meeting PGT indications, donor oocytes, untreated uterine anomalies/hydrosalpinx, or contraindications to pregnancy/ART.

Randomization/interventions: Participants will be randomized 1:1 to NICS-AI-guided selection or morphology-based selection. In the NICS-AI arm, culture-medium DNA is tested and an AI-derived composite implantation score ranks embryos; controls use morphology alone (tie-break by cryopreservation order).

Outcomes/analysis: The primary endpoint is live birth after the first SBT (delivery with ≥1 live-born infant per transfer cycle, per randomized participant). Secondary endpoints include first clinical pregnancy, early miscarriage (<12 weeks, excluding biochemical pregnancy), ongoing pregnancy to 12 weeks, and cumulative pregnancy/live birth outcomes within 1 year (≤3 SBTs from one retrieval). Safety includes fetal malformations and neonatal outcomes through 1 year postpartum.

Inclusion Criteria:

1. Conventional IVF insemination;

2. Meeting either of the following:

   1. Advanced maternal age: female age 35-43 years;
   2. Recurrent miscarriage: ≥2 spontaneous pregnancy losses (<28 gestational weeks), including biochemical pregnancy (hCG >25 IU/L) ;

3. Willingness to culture all Day 3 embryos to the blastocyst stage in the fresh cycle, or to culture ≥6 embryos (with at least one embryo ≥7 cells), and to cryopreserve all blastocysts as single-blastocyst vitrification;

4. Willingness to undergo frozen-thawed single-blastocyst transfer;

5. At least two blastocysts formed on Day 5/Day 6 from 2PN fertilization, with morphological grading ≥4BC/4CB;

6. Provision of written informed consent.

Exclusion Criteria:

1. Any use of intracytoplasmic sperm injection-based fertilization, including but not limited to ICSI, TESA, and PGT-related cycles;
2. Known monogenic disorders or chromosomal abnormalities at enrollment;
3. Patients who use donated eggs to achieve pregnancy;
4. Definite conditions affecting uterine cavity anatomy or endometrial receptivity, such as untreated uterine malformations (e.g., septate uterus, unicornuate uterus, didelphys uterus) or untreated hydrosalpinx;
5. Contraindications to pregnancy or to assisted reproductive technology;
6. Any other condition deemed by the investigators to make the participant unsuitable for this study.