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In vitro fertilisation (IVF), together with intrauterine insemination, is the main technique for Assisted Reproductive Technologies (ART).
IVF enables the gametes (oocytes and sperm) to meet outside the female reproductive system, by bringing them together in the laboratory. There are two main IVF techniques: “classic” (or “conventional”) IVF, and IVF with ICSI (Intra-Cytoplasmic Sperm Injection) which entails the micro-injection of a sperm cell into an ovum. Whichever technique is used, the goal is to obtain embryos, which can then be placed in the uterus by means of embryo transfer. In the vast majority of cases, IVF is preceded by the stage of ovulation stimulation, which makes it possible to obtain several oocytes, and therefore potentially several embryos.

Ovarian stimulation





Gamete collection and preparation

  1. Collection and preparation of oocytes
    Oocytes are collected in the operating theatre by means of a trans-vaginal ovarian puncture (watch the video). The follicular fluids containing the oocytes are collected by the gynaecologist and taken to the laboratory. Here the cumulus-oocyte complexes (oocytes surrounded by their follicular cells) are removed from the follicular fluid, one at a time, and then stored in a culture medium in an appropriate environment pending their fertilisation.
  2. Collection and preparation of sperm
    In most cases, these are the partner’s sperm collected on the same day as the ovarian puncture in the form of masturbatory ejaculate. More rarely, they are previously frozen sperm (ejaculated or obtained surgically, and possibly from donors, see the specific pages of this website). In all cases, the sperm used for IVF are prepared on the same day. Different techniques are possible, but they aim seek to select mobile sperm, at the same time, eliminating other components of the semen (seminal fluid, other cells).



“Conventional” in vitro fertilisation

About 1 to 4 hours after the ovarian puncture, the cumulus-oocyte complexes are fertilised with the prepared sperm. The stages of fertilisation take place just as they would in the woman’s body (see the specific page of this website). After 18 to 20 hours, oocytes are released from the follicular cells of the cumulus-oocyte complexes and examined for signs of fertilisation, i.e. the formation of 2 pronuclei. This confirms that the encounter between the egg and the sperm has taken place normally and the fertilised ovum is now called a zygote.

In vitro fertilisation with ICSI

About 1 to 4 hours after the ovarian puncture, the follicular cells surrounding the ova are removed. The mature ova are then fertilised using the ICSI technique. This consists of using a micro-pipette to place a previously immobilised sperm cell inside the cytoplasm of each of the egg. After 18 hours, signs of fertilisation are looked for, in order to ensure that the union between the sperm and the egg has taken place successfully.

Whether IVF or ICSI are used, not all oocytes are necessarily mature at the time of fertilisation, and not all of the mature eggs will necessarily be fertilised normally. It is therefore usual to obtain fewer zygotes than the number of oocytes that were collected at the time of the ovarian puncture.

Embryo culture

Throughout the IVF process, the embryos are kept in an environment that aims to reproduce natural conditions and ensure optimum development. For this reason, the embryos are placed in culture dishes containing an appropriate medium. These dishes are then placed in incubators which maintain physiological conditions in terms of temperature, atmospheric gases and humidity.
The embryos are stored in the laboratory until they are transferred and/or frozen, which can take place either on day 2 or on day 3 (i.e. 2 or 3 days after the ovarian puncture), or after extended culture until day 5 when they have reached the blastocyst stage (see the page of this site “Fertilisation and Embryo Development”). During the embryo culture in the IVF laboratory, the embryos are observed once a day at specific times in order to assess their development and their morphology. On day 2 and day 3, the morphological criteria for describing the embryos include: the number of cells (called blastomeres), the symmetry of the divisions and the presence of any fragments. On day 5, other morphological criteria are used to describe any blastocysts that have been obtained.

These morphological criteria are often incorrectly defined as “embryo quality criteria”. In fact, they are merely used to assess an embryo’s capacity to bring about a pregnancy and are therefore used by reproductive biologists to select embryos for transfer and freezing. However, they are absolutely inadequate for predicting whether a pregnancy will really take place, and they certainly cannot predict or describe the quality or worth of the unborn child! An “average quality” embryo is less likely to lead to a pregnancy, but if it does so, it will produce a baby that is just as healthy as a “good quality” embryo.

Embryo transfer

Embryo transfer entails placing one (or two) embryos into the uterus. It is a painless outpatient procedure that does not require hospitalization or anaesthesia. The reproductive biologist selects the embryo(s) to be transferred and places them in a thin catheter, and the gynecologist transfers the embryo(s) to the uterus using the catheter, which is inserted through the uterine neck and guided by ultrasound.
Depending on the context (the number of attempts already made, the patient’s age, the number and the morphology of embryos, the policy of the ART centre), embryo transfer may be scheduled on day 2, day 3 or day 5, and can involve 1 or 2 embryos.
In some cases, IVF may not lead to an embryo transfer. This happens when no embryo can be transferred (due to fertilization failure or unsatisfactory embryo morphology), or when transfer is not advisable for medical reasons (risk of ovarian hyperstimulation, inadequate progesterone levels, etc.). In this case, all the embryos obtained are frozen, and this is what is defined as “freeze all” or postponed transfer.



Embryo freezing
Freezing makes it possible to store embryos for later transfer, either if there is the intention to obtain a second pregnancy, or if no pregnancy is achieved at the time of transfer, or if a “freeze all” strategy is adopted. The frozen embryos are stored in liquid nitrogen at -196°C in specially designed storage tanks. Embryo freezing constitutes a huge step forward in IVF treatment, as it increases the cumulative chances of a successful puncture. This has been the case especially since the development of the vitrification technique, which has obtained excellent results in terms of survival rates and pregnancy rates. In fact, the pregnancy rates for frozen embryo transfer are now identical to those for the transfer of non-frozen embryos.


Public consultations (sector 1, without exceeding fees): contact the appointment office of Antoine Béclère Hospital: 01 41 07 95 95


Private consultations (sector 2, with overruns): contact Ms. Céline Delattre at or celine.delattre@aphp.fr