So, it’s back to square one.

We’ve had a month or so to reflect on our last unsuccessful IVF attempt; this week involved a meeting with the Doctor to discuss our next steps. Tuesday afternoon saw us in the same waiting room again (noting that they’ve still not updated the magazines). Mrs Astronomer was a bit nervous, but coped.

The doctor was very pleasant, and only got my name wrong once (once again giving the distinct impression that husbands are only there for moral support during the IVF process and at most other times may be ignored). In the corner of the room sat a student doctor wearing a very large pair of glasses, who was dutifully scribbling notes whenever the doctor said anything she considered to be of note, which was everything. (Case notes: 25 Apr 17, IVF meeting re. Mr + Mrs Astro, couple in early 30’s one unsuccessful attempt at IVF looking at rnd2. Note Dr Smith warm, welcoming, puts couple at ease. Male partner seems mildly put out at something. Note textbook delivery by Smith of all relevant information to female partner; most likely of the two to remember it all).

As expected, the clinic doesn’t know why our last round of IVF failed; it is, at this point, just one of those things. Statistics work that way. He talked us through the polyp (which was almost certainly not the cause of failure, and may just be a fold in the lining of the womb). Mrs Astro took all this in, tears slowly rolling down her cheeks. Without drawing attention to the fact, the Doctor pushed a box of tissues across the desk to her. (Note – tissues deployed at first sign of tears. Has dramatic effect on stemming crying from female partner). He then went on to discuss our options. We’d used the best quality blastocyst in our last attempt – our ‘A’ candidate – and now we had two left, ‘B’ and ‘C’. This is a sliding scale in measuring blastocyst quality; A through D, where A has a nice distinct differentiation between the cells which will become the embryo and the placenta, and in D the two groups of cells are indistinguishable. Inserting an individual cell has a 50% chance of success individually.

This presents us with a choice.

The doctor started to talk about the statistics of success, and I started to think. (Note – the male partner seems extremely distracted, staring into the middle distance. The female subtly pokes him a few times but it makes no difference). We now have a choice about how we proceed. Do we insert them individually – take another go of IVF with blastocyst B, and if that doesn’t work, insert C later – or do we fire the remaining to shots in one volley and insert them both at the same time? There are arguments for and against for both. Brace yourself, I’m gonna break out statistics. (Note – extremely distracted, staring into middle distance, dribbling). If we insert the two remaining blastocysts individually, each has a probability of success of 50%. If we insert them both at the same time, the odds of having a successful pregnancy rises to 60%.

No brainer, right?

Well, not really. Remember, what we’re after here is a pregnancy. If we insert them in two separate rounds, the odds of getting at least one pregnancy rises to 75%. Measured over several goes, the odds of an event happening at least once increases as the number of individual events goes up. Don’t believe me? Flip a fair coin 100 times and I guarantee you that you will get at least one heads. The odds of it not happening – of getting 100 tails – are about 0.000000000000000000000000000078%. (More or less. I may have missed a zero somewhere typing that all out in full). The odds of a normal, un-IVF’d “vanilla” pregnancy (where conception takes place in utero rather than in vitro) is approximately 20% for any given ovulation cycle. Taking this statistic and running with it, if you have unprotected sex on every single cycle for a year at ovulation your overall odds of pregnancy that year is 93.13%. This statistic will go down as the female half of the equation ages; the best time for fertility is immediately after puberty, decreasing  in a typical exponential decay, reaching about 20% in her late 20’s/early 30’s and continuing to drop off after that until the menopause. But despite it dropping off, if you have unprotected sex for a year in your late 20’s/early 30s, pregnancy’s not quite guaranteed, but you’d be an idiot not to use protection if you didn’t want kids. Therefore, the odds of the two 50/50 events turning out positive at least once is 75%.

So, hurrah for statistics.

But what about the odds of fertilising both eggs? What’s the best way of doing that? These are our babies after all, and we would like to have both of them, if possible. The odds of both eggs being fertilised if we insert them one after the other (so, insertion, pregnancy, childbirth, insertion, pregnancy, childbirth) is 25% – again, the same logic; the odds of something happening again and again and again diminish as it goes on. Each event, taken individually, has a probability of 50%, but you wouldn’t bet on a coin coming up heads every single time for 100 coin tosses. Even 25% isn’t a sure fire thing. We have a 75% chance of getting one baby and a 25% chance of getting them both using this method.

Remember what I said about inserting both eggs at once? If we insert both eggs at the same time, the odds of a successful pregnancy rises to 60%. If you want a single baby, multiple insertions of single eggs is the way ahead, by a good 15%. But if there’s two eggs inside her at any one go… any successful pregnancy has a 50% chance of producing twins. Therefore, the odds of both blastocysts surviving to childbirth is now increased to 30%: a 60% chance of a single pregnancy, multiplied by the 50% odds of twins.

Therefore, we have a choice. A 60% chance of pregnancy with a 30% chance of both blastocysts being successful, versus a 75% chance of a single pregnancy coupled with a 25% chance of both blastocysts surviving to pregnancy. It’s either or.

There are, of course, other factors.

This analysis doesn’t take into account the fact that blastocyst C is getting a bit far down the spectrum of quality, and may need all the help it can get from its B class sibling. 50% success is an average; some blastocysts will be above it, others below. I suspect that 50% chance of success may be over-egging it slightly in this case – it’s not exactly D quality, but still – we would like the best chance for both our blastocysts to become babies; a single insertion would statistically be the best way of achieving that outcome. On the other hand, add in the fact that twins add complexity, which is not what we want for IVF. Coupled to that is the practical considerations of cost; a single round of IVF without all the drugs could cost us in the realm of £2,000, now we’ve already used up our NHS free roll of the dice. We’re buying a house at the same time, remember, so we need all the cash we can get. There’s no clear cut answer, we just need to think about it over the course of the next few weeks. We have a decent chance of getting one pregnancy, or a small chance of getting two by placing all our eggs in one basket. Perhaps I’m over thinking the problem and over analysing; I do have a habit of doing that.

Thinking about it, I shouldn’t really call Mrs Astro “Basket”, she might get annoyed….