# Oocyte Retrieval and Embryo Transfer

> NEET-PG Obstetrics and Gynaecology notes on IVF oocyte retrieval and embryo transfer: timing, fertilisation, culture stages and transfer technique.

- Canonical URL: https://prepelephant.com/topics/neet-pg/obstetrics-and-gynaecology/oocyte-retrieval-and-embryo-transfer
- Exam / course: NEET-PG · Subject: Obstetrics and Gynaecology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-08
- Last updated: 2026-10-08
- Reference basis: Speroff's Clinical Gynecologic Endocrinology and Infertility; Williams Gynecology; D.C. Dutta's Textbook of Gynecology
- How to cite: "Oocyte Retrieval and Embryo Transfer", PrepElephant, https://prepelephant.com/topics/neet-pg/obstetrics-and-gynaecology/oocyte-retrieval-and-embryo-transfer

## Direct answer

Oocyte retrieval is ultrasound-guided transvaginal aspiration of mature follicles, performed about 34 to 36 hours after the trigger dose of hCG or GnRH agonist. Oocytes are fertilised by conventional IVF or ICSI, and embryos are cultured to the cleavage or blastocyst stage. The selected embryo is transferred into the uterine cavity under ultrasound guidance, and luteal phase progesterone support follows transfer.

## What you must remember

- **Trigger timing:** hCG or GnRH agonist is given once follicles are mature, and retrieval follows about 34 to 36 hours later, before ovulation.
- **Retrieval technique:** a needle passed through the vaginal fornix under ultrasound guidance aspirates each follicle, under sedation or anaesthesia.
- **Fertilisation check:** conventional IVF or ICSI is used, and pronuclei are assessed about 16 to 18 hours later.
- **Culture stages:** cleavage stage on day 2 to 3, and blastocyst on day 5 to 6, grading guides embryo choice.
- **Transfer technique:** a soft catheter is placed in the upper uterine cavity under ultrasound, avoiding trauma to the cervix and fundus.
- **Luteal support:** progesterone, started around retrieval and continued after transfer, supports the endometrium, since stimulation can impair normal luteal function.
- **Ovarian hyperstimulation syndrome:** ascites, haemoconcentration and thromboembolism; a GnRH agonist trigger and freeze-all strategy reduce the risk.

## From stimulation to transfer

A woman with unexplained infertility has mature follicles on ultrasound, and the trigger is due. Each step must be timed so the oocytes are retrieved before ovulation. The sequence below follows the standard laboratory and clinical workflow, with each stage documented so that outcomes can be audited.

1. **Trigger:** hCG or GnRH agonist is given when follicles are mature, with retrieval timed 34 to 36 hours later.
2. **Retrieval:** transvaginal ultrasound-guided aspiration is done under sedation or anaesthesia, and follicular fluid goes to the embryologist.
3. **Identification:** the embryologist finds cumulus-oocyte complexes, then the mature metaphase II oocytes.
4. **Fertilisation:** conventional IVF or ICSI is performed, and pronuclei are checked the next day.
5. **Culture:** embryos are cultured under controlled conditions to the cleavage stage on day 2 to 3, or to the blastocyst stage on day 5 to 6.
6. **Transfer:** an ultrasound-guided soft catheter places the chosen embryo in the uterine cavity, followed by luteal progesterone.

## Where the exam tries to catch you

ART questions test timing, the complication to fear and the technique that avoids injury.

- **Trap:** retrieving oocytes too early or too late after the trigger — **Correct:** about 34 to 36 hours after hCG or GnRH agonist, retrieval must precede ovulation.
- **Trap:** dismissing ovarian hyperstimulation as a minor complication — **Correct:** severe OHSS causes ascites, pleural effusion, haemoconcentration and thromboembolism, so a freeze-all strategy is safer.
- **Trap:** forcing a difficult cervix during transfer — **Correct:** a soft catheter guided by ultrasound avoids trauma, and a mock transfer beforehand helps.

## Frequently asked questions

### When is oocyte retrieval performed after the trigger dose?

Oocyte retrieval is performed about 34 to 36 hours after the trigger dose of hCG or GnRH agonist. This timing retrieves oocytes just before ovulation. Retrieval is transvaginal and guided by ultrasound.

### How are embryos chosen for transfer in IVF?

Embryos are chosen by morphological grading on day 2 to 3 or day 5 to 6, and sometimes by preimplantation testing where indicated. The best-graded embryo is usually transferred. Laboratory practice and national regulations guide the final choice.

### What is the difference between IVF and ICSI?

Conventional IVF places sperm and oocytes together for fertilisation, while ICSI injects a single sperm directly into each mature oocyte. ICSI is preferred for severe male factor infertility. Fertilisation is checked the next day in both methods.

### Which complication is most feared after oocyte retrieval?

Ovarian hyperstimulation syndrome is the most feared complication of stimulation and retrieval. It causes ascites, haemoconcentration and, in severe cases, thromboembolism and renal impairment. A GnRH agonist trigger and a freeze-all strategy reduce its risk.

### Why is luteal progesterone given after embryo transfer?

Progesterone is given around retrieval and after embryo transfer to support the endometrium, since ovarian stimulation can impair normal luteal function. It is given vaginally or intramuscularly, continued until a pregnancy test or per the local protocol.