IVF – how the treatment works
An IVF treatment begins with ovarian stimulation. Follicles are stimulated to mature using injections of hormones that naturally occur in each menstrual cycle. Follicle growth and the number of developing follicles are monitored by ultrasound. When enough follicles have reached the right size, a date is scheduled for egg retrieval.
Egg retrieval
At Göteborgs IVF Klinik, egg retrievals are performed in the morning/late morning. Because we value privacy, you (and any partner) will have your own private recovery room before and after the procedure. When you arrive, your ID is checked and you change into a gown to wear during the retrieval. A partner, if applicable, either hands in a pre-collected semen sample to the laboratory or produces a sample on site.
You will receive a peripheral IV cannula (PVK) so we can administer medication directly into the bloodstream. Just before entering the procedure room, you’ll be asked to empty your bladder. In the room, your ID is checked again and the embryologist will introduce themselves. Your blood pressure, pulse and oxygen saturation are measured. Before the doctor administers local anaesthetic in the vaginal wall, you receive pain relief through the IV. While the anaesthetic takes effect, an ultrasound is performed and your follicles are counted again.
During egg retrieval, the fluid in all mature follicles is aspirated with a thin needle through the vaginal wall. On average, oocytes are retrieved from about 80% of the mature follicles (this varies with ovarian reserve, age, and individual factors). The first oocyte is shown on a screen so you can see it. When the retrieval is finished, you return to your room. As soon as all oocytes have been counted, you will be told how many were collected. Before you go home, you receive verbal and written information about the number of eggs, the semen analysis result, and the plan going forward.
The sperm’s journey
Fertilisation
After retrieval, the oocytes are placed in culture dishes and kept in a heated incubator. After a few hours they are fertilised either by standard IVF (eggs and sperm are placed together and the sperm swim to the egg) or by ICSI (intracytoplasmic sperm injection).
With ICSI, the embryologist selects a morphologically normal, well-moving sperm and injects it into the egg. Only mature eggs can be fertilised; egg maturity is often confirmed at the time of ICSI, if ICSI is used.
If fertilisation occurs, two pronuclei (one from the sperm and one from the egg) can be seen the day after retrieval. Later that day, the pronuclei fuse and the first cell division takes place, forming an embryo. On average, about 65–70% of mature eggs fertilise normally.
Embryo culture
Over the next days, the embryo continues dividing—roughly once per day. Because day 0 is the day of egg retrieval, by day 2 an optimally developing embryo has 4–6 cells, and by day 3 8–12 cells.
We culture embryos in an incubator with time-lapse technology, which lets us observe development without disturbing the culture conditions. This helps us evaluate which embryo has the highest likelihood of leading to pregnancy.
Which day is best for embryo transfer?
At retrieval, we provisionally schedule an embryo transfer on day 2 or day 3. Because development is evaluated day by day, the planned transfer day may change to maximise pregnancy chances. You may be informed—up to the same morning as the provisional transfer—that we recommend moving the transfer.
On day 1 (the day after retrieval) we see how many embryos fertilised normally. If five or more eggs fertilised normally and there are no special circumstances or preferences, we usually recommend extended culture to the blastocyst stage (day 5) before transfer. When there are five normally fertilised eggs on day 1, the chance that at least one embryo will progress well to day 5 is on average about 85%. During culture, natural selection occurs: stronger embryos continue developing while others arrest.
If fewer than five eggs fertilised normally on day 1, we generally recommend transfer on day 2 or day 3 to optimise the chance of pregnancy. On average, ~40% of normally fertilised eggs reach the blastocyst stage, but this varies widely between patients and even between cycles.
Embryo transfer
For transfer, the age of the embryo is synchronised with the uterine lining. The embryo is drawn into a thin catheter and gently placed in the uterine cavity through the cervix. The embryo then moves and finds its optimal place to implant.
A pregnancy test is taken 14 days after transfer. The miscarriage risk is the same as in a spontaneous pregnancy—IVF increases the chance of achieving pregnancy, but it does not lower the inherent miscarriage risk.
What are the chances of pregnancy?
With a day 2 or day 3 transfer and a good-quality embryo, the average clinical pregnancy rate is around 30% for a woman of about 35 years.
With a blastocyst (day 5) transfer, the average clinical pregnancy rate is around 50% for a woman of about 35 years.
As maternal age increases, pregnancy chances decrease (fewer eggs and a higher proportion of chromosomally abnormal eggs) and miscarriage risk increases. IVF cannot reduce the age-related miscarriage risk; it improves the chance of pregnancy by retrieving multiple eggs at once, fertilising them, culturing them, and transferring and/or freezing the best embryos.
What happens to embryos that are not transferred?
If there are additional good-quality embryos on day 5 or 6, they are frozen. If pregnancy does not occur after the first transfer, a frozen embryo can be thawed and transferred in a later cycle. At our clinic, about 50% of patients obtain one or more blastocysts to freeze; the likelihood is higher in younger women and with a stronger ovarian reserve.
A frozen embryo has a 90–95% chance of surviving thawing in Sweden; our survival rate is 98%. By Swedish regulation, embryos can be stored for up to 10 years, and current guidance allows transfers up until the woman is 44 years old (not after her 45th birthday).
It is not possible to determine an embryo’s sex by eye during the culture period.