How many eggs are needed to produce an embryo? The figures, step by step

‘Fifteen eggs – is that good? How many embryos will that make?’ That’s the question on everyone’s mind on the evening of the egg retrieval. The next day, we find out how many have been fertilised; five days later, how many have developed into blastocysts. With each update, the number drops, and many patients experience this decline as a failure. Yet this decline is predictable, and laboratories have reference values to determine whether it remains within the normal range.

The stages at which eggs are ‘lost’

1. Maturity. Not all the eggs retrieved are mature. Only those in metaphase II can be fertilised.
2. Fertilisation. Some of the mature eggs are fertilised normally, in both conventional IVF and ICSI.
3. Development to the blastocyst stage. Between the first and the fifth or sixth day, many embryos cease to develop. This is often the most selective stage.
4. Chromosomal normality. Among the blastocysts, a proportion carries a chromosomal abnormality, which will prevent implantation or lead to a miscarriage. This proportion depends mainly on the age of the woman who produced the eggs.

Laboratory reference values

In 2017, a group of experts convened by the ESHRE established performance indicators for IVF laboratories in the ‘Vienna Consensus’. These serve as a benchmark for determining whether a result falls within the normal range. For women under 40 using their own eggs, without genetic testing:

These are averages, not guarantees: each cycle varies around these figures. However, a significant and repeated deviation warrants an explanation.

An example: fifteen eggs

Let us apply these rates to fifteen eggs retrieved, using ICSI, from a woman under 40:

Fifteen eggs therefore usually yield three to six blastocysts. This is not an abnormal loss: it is a selection process which also occurs during natural conception, simply without us being aware of it.

Age mainly affects the final stage

The first three stages vary from one cycle to another and from one laboratory to another. The final stage depends mainly on age. In an American study analysing more than 15,000 blastocysts, the proportion of chromosomal abnormalities was lowest between the ages of 26 and 30, and then increased with age. Among patients whose blastocysts had been analysed, the probability of having none that were chromosomally normal was 2–6 per cent between the ages of 26 and 37, 33 per cent at 42, and 53 per cent at 44.

This is why, given the same number of eggs, the chances are not the same at the age of 32 as they are at 42. PGT-A makes it possible to identify which embryos are normal, without creating any new ones: see the article on PGT-A.

How many eggs should you aim for?

More eggs mean more embryos, up to a certain point. A British study covering more than 400,000 cycles showed that the chances of a live birth per fresh IVF cycle increased up to around 15 eggs, plateaued between 15 and 20, and then declined beyond that, whilst the risk of hyperstimulation continues to rise. With 15 eggs, these chances were estimated at 40 per cent between the ages of 18 and 34, 36 per cent between 35 and 37, 27 per cent between 38 and 39, and 16 per cent from the age of 40 onwards.

The aim of stimulation is therefore not to achieve the highest possible number, but to ensure a sufficient and safe response. For egg freezing, a large Spanish study published in 2016 provides a rough guide: up to the age of 35, the cumulative chances of a live birth rose from around 15 per cent with 5 vitrified eggs to 41 per cent with 8, peaking at around 85 per cent with between 10 and 15 eggs; from the age of 36 onwards, they were significantly lower, at around 20 per cent with 8 eggs and 36 per cent at best.

And what about egg donation?

With a young donor, all stages are generally more favourable, particularly the final one: the proportion of chromosomally normal blastocysts corresponds to the donor’s age, not the recipient’s. Ask the clinic how many eggs the donor must provide as a minimum, whether this number is specified in the contract, and what happens if it is not met. Details of the chances are set out in the article on egg donation success rates.

What to ask the clinic

• How many eggs were mature?
• How many were normally fertilised?
• How many reached the blastocyst stage, and what was their quality? See how to interpret the grades.
• Do these figures correspond to the laboratory’s usual rates?

A result well below the reference values for a single cycle warrants an explanation and, in some cases, a change in protocol; see poor response to stimulation. If you’d like us to look through the report from your last cycle together, please write to me.

Frequently asked questions

Source: https://fertilitegrece.com/en/blog/how-many-eggs-for-one-embryo/ — Triada Baloukoudis, IVF patient coordination in Greece. General information, not medical or legal advice. Printed on

Triada Baloukoudis
Independent IVF patient coordinator in Thessaloniki, with 24 years of experience supporting patients travelling from abroad. More · Contact · Facebook