In-Vitro Fertilization (IVF)



What is IVF?

In-vitro fertilization and embryo transfer (IVF), also known as ‘test-tube baby’, is an effective treatment for infertility. It involves collecting eggs from the woman’s ovaries, fertilizing the eggs with the man’s sperms in the laboratory, culturing these fertilized eggs to become embryos and returning them into the woman’s womb. It was originally developed to help women with blocked fallopian tubes to conceive, but has since been expanded to treat couples with various causes of infertility.

Schematic diagram of IVF treatment
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Who may need IVF?

What does IVF involve?

(I) Ovarian Stimulation

(II) Egg Collection

(III) Fertilization

(IV) Embryo Culture

(V) Embryo Transfer

(VI) Embryo Freezing

(I) Ovarian Stimulation

In order to collect more eggs, fertility drugs are used to stimulate the ovaries. There are different stimulation protocols. The most commonly used one is the antagonist protocol.

Ovarian Stimulation
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Antagonist protocol: The woman takes daily ovarian stimulation drug injections in the beginning of her cycle to boost the growth of follicles (or eggs). Another injection drug, known as an antagonist, is added in the latter part of the stimulation period to prevent the eggs from being released too soon. The woman needs ultrasound scans and blood tests to monitor the growth of the follicles. When the eggs are ready, an ovulation trigger injection is given to complete the final maturation of the eggs and egg collection can be arranged.

Other less commonly used protocols include: 

  • Long protocol

  • Short protocol

  • Minimal stimulation protocol

  • Random start protocol

  • Double stimulation protocol

(II) Egg Collection

The egg collection procedure is performed under ultrasound guidance. An ultrasound probe is inserted into the vagina to identify the follicles. A thin needle is then inserted into an ultrasound guide to go through the vagina and into the follicle (Egg collection YouTube Link). The follicular fluid is aspirated and collected into a test tube. An embryologist then looks at the follicular fluid under a stereomicroscope to collect the eggs.

Egg Collection


Egg Collection (OPU)

(Egg collection YouTube Link)

Egg Collection

An embryologist is looking down a stereomicroscope, checking follicular fluid to see if an egg can be found.

The egg collection procedure takes around 30–45 minutes. It is a painful procedure, and therefore anaesthesia is given. The woman can go home after resting in the IVF centre for a few hours, and return to work the next day.

(III) Fertilization

The man has to produce a semen sample on the day of the egg collection. The semen sample is processed, and the sperms are used for insemination with one of the following methods:

  1. Conventional IVF

    Conventional IVF is a process by which the sperms and eggs are mixed together, and the sperms penetrate the eggs by themselves (Conventional IVF YouTube Link). This insemination method is suitable for couples with adequate active and normal sperms.

Conventional IVF


Conventional IVF

  1. Intracytoplasmic sperm injection (ICSI)

    Intracytoplasmic sperm injection (ICSI) is a procedure involving the direct injection of a single sperm into an egg to assist fertilization (ICSI YouTube Link). ICSI is usually performed in couples with specific indications:

    • Severe male factor infertility;

    • Previous conventional IVF had none or very few eggs fertilized;

    • Sperms collected surgically;

    • Planned PGT;

    • Frozen-thawed eggs;

    • Frozen-thawed sperms that are not as active.


Intracytoplasmic sperm injection (ICSI)

(IV) Embryo Culture

Embryo culture

Embryo development

Embryo grading

The day of the egg collection is called Day 0 in the timeline of embryo development. On Day 1, embryologists check the eggs to see if fertilization is successful. On Day 2, the fertilized eggs undergo cell division and become embryos. The embryos can be cultured for up to 5 days when they are called blastocysts. They can be transferred back into the uterus on either Day 2, Day 3 or Day 5.

Embryo development (YouTube Link)

Schematic diagram of IVF treatment
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Embryo grading

1. Cleavage stage embryos (e.g. Day 3 embryos)

A cleavage stage embryo is assessed by the number of cells in the embryo, whether the cells are even in size, and the degree of fragmentation.

Cleavage stage embryos
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2. Blastocyst stage embryos (e.g. Day 5 embryos)

Blastocyst stage embryos

A blastocyst is assessed by the development of cavity, inner cell mass (ICM) and trophoectoderm:

  1. Degree of expansion of the cavity. This is graded on a scale of 1-6:

    1 = the cavity is beginning to form

    2 = the cavity fills 1/3 of the embryo

    3 = partial expansion, the cavity fills 70% of the embryo

    4 = fully expanded cavity

    5 = the embryo has expanded and the zona pellucida splits open

    6 = the embryo has completely hatched from the zona pellucida

  2. Appearance of the inner cell mass (ICM) (the cells that will grow to become the baby). This is graded into either A, B, or C:

    A = well-defined clump of cells

    B = less well defined; may be grainy in appearance

    C = a few dark cells , appear degenerative

  3. Appearance of the trophoectoderm (the cells that will form the placenta). This is also graded into either A, B or C:

    A = many smooth cells, equal in size, forming a neat layer

    B = irregular cell layer, some grainy cells

    C = very irregular cell layer, cells may be dark and / or grainy

a. Degree of cavity expansion

Degree of cavity expansion
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b. Inner cell mass (ICM)

Inner cell mass (ICM)

c. Appearance of trophoectoderm layer

Inner cell mass (ICM)

(V) Embryo Transfer

During embryo transfer, a small tube (catheter) is inserted through the cervix (the neck of the womb) and the embryo(s) is/are put into the womb cavity. The procedure is similar to taking a Pap smear. Anaesthesia or analgesia is usually not required. The woman can go home after embryo transfer and resume work the next day. She has to insert hormone pessaries into the vagina to help the lining of the uterus. A pregnancy test can be done usually around 2 weeks later.

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(VI) Embryo Freezing

After embryo transfer, any remaining good quality embryos are frozen for use in the future, in case treatment does not work or to try for a sibling.

Embryo Freezing

In HKARC, the embryos are frozen by vitrification (rapid freezing)
and stored in liquid nitrogen tanks. The vitrification method has
a higher embryo survival rate on thawing as compared to the
old-fashioned slow freezing method, and has therefore become
the preferred method of freezing embryos nowadays

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How long can the embryo be stored for?

Embryos can be stored for up to a maximum of 10 years. Patients in certain circumstances, such as cancer patients, can store their embryos for up to 10 years or when they are 55 years old, whichever is later.

Reason for embryo storage

Maximum storage period

Patients in certain circumstances

10 years, or up to 55 years old, whichever is later

All other patients

10 years