Why would you not get pregnant in a given month, if all was well?

[ProbablyaStupidQuestion]

I'm trying to google this, just out of curiosity but all I'm getting is stuff about infertility or issues that can cause it took take a while to get pregnant. I get all that, my question is why would you not get pregnant on a given month, if all was well health wise, no fertility issues on either side, and you had sex at the exact right time with ovulation. Does this happen? Or is it that the people who don't conceive in a given month whilst trying, are either not timing it right, not ovulating when they thought, or there is a fertility issue on both sides?

Probably a stupid question so I've named changed out of embarrassment

I don't mean this to sound insensitive by the way, I struggled for a year to conceive my first but I have PCOS. I'm starting again for no2 and I know it'll probably take a while due to that, but it made me wonder is all

I’m not an expert, but as I understand it even healthy men can have a proportion of sperm which aren’t quite right or not compatible with the egg in some way. If one of them hits the egg first then the pregnancy won’t go ahead. And even young healthy women can have the odd substandard egg.

You never have more than a 25% chance and that 25% assumes perfect timing with two perfectly healthy adults. Chances are probably lower than this for most people and that's why it take 6 months to a year to get pregnant.

You need the right environment, the right sperm and the right egg and there are so many tiny things which can affect that formula.

Even if you do everything correctly and the sperm meets the egg, there's only a 25-30% chance of fertilisation.

This gave me some comfort

well, because it is not a perfect procedure. It requires the perfect sperm to hit the perfect egg at the perfect time.

Human bodies are not perfect, and not every single sperm or egg is either, and the conditions in your womb may not be 100% perfect.
Not for any serious or medical reason, just because bodies are like that.

Also there is only a 25% chance in each cycle, so it’s mostly down to luck too.

I think a lot of women think they know exactly when they’re ovulating but it’s very difficult to actually know for sure. I used to get all the telltale ovulation symptoms around CD15 and we would DTD in the run up and either side but then stop from about CD20 onwards as I wouldn’t be so much in the mood. We weren’t getting pregnant and I had no idea why. On the month that I did get pregnant we randomly did it on CD21, my period was late but I was only getting very faint lines by CD30 (day my period was due). Proper positives 4-5 days later. When I went for my dating scan they said my dates were out even though I definitely knew the day of my LMP. So it basically seems like I was ovulating much later that I thought even though I was getting all the ovulation signs at the normal time.

There are things you can do to improve the health of your eggs and his sperm. Helathy lifestyles and eating, vitamin and mineral supplements, dropping alcohol (both of you), that sort fo thing. But that is about boasting your chances. It still isn't guaranteed.

In addition to the above, about 1 in 3 fertilised eggs don't implant - so sperm met egg, but if it never implants you wouldn't ever know that (you wouldn't get as far as a pregnancy test being positive, even the most super sensitive kind). So if a healthy young couple have a 30% chance of getting pregnant each month (which is what the statistics say) then that actually means that sperm successfully met egg around 60-65% of the time, so timing was just fine, but a lot of those didn't make it to implantation, usually due to the issues of imperfect sperm or egg highlighted above.

Chemical pregnancies happen so the sperm met egg but something wasn't right and it couldn't continue. I assume it happens earlier than would show up on a test sometimes.

That 25% figure has to be an average, some people are much higher and some lower, sorry to people with fertility issues but so far I'm 2 for 2 on it just working first time (both technically contraceptive failures )... I can't just be that "lucky"??

The egg is only viable for 24 hours, after that time period it can't be fertilised, so if the sperm are too slow, or you haven't had sex within 24 hours of the exact time you ovulate the egg won't be fertilised. Sometimes the egg is fertilised but it may have an abnormality so doesn't implant in the womb. Apparently this is more common than you would think. So you may have had a fertilised egg that doesn't stick without ever knowing it. Also I've read cortisol (the stress hormone) can stop an egg implanting but I've no idea how true that is. Also some lubricants can slow sperm down and lessen their mobility

Thanks all! Can't believe it's only 25% even if you time it right, not sure if that makes me feel better or worse

Timing has to be perfect, plus about half of the eggs that do get fertilised either don't implant or don't proceed beyond a few days apparently.

By the way, I get pregnnat very quickly, usually first month, but then loose them.
So I have had 7 pregnancies, but have 3 kids. The others all lost at 6-12 weeks.

So my body does well on the conceive part, but I sometimes think it would have been easier to have fewer better quality pregnancies if you see what I mean.

I track my bbt everyday, last time when I did eventually conceive it was textbook, temps rising at the exact right time so I'm fairly confident I know when I ovulate. I ovulate later this week so we're trying everyday and I just really want a one month wonder, the stress of last time was awful. I will remain realistic though as it is unlikely

@probablyastupidquestion I wondered this for ages too, then someone recommended watching the 'fertility' episode of 'Sex, Explained' on Netflix. I don't think I quite appreciated how difficult it is for the sperm to actually get to the egg...they compared it to a labyrinth. Apparently the reason is that if two sperm get to an egg at roughly the same time, it won't fertilise.

Watch The Great Sperm Race. It's really good and I learned a lot about conception from it.

m.youtube.com/watch?v=4qegAMEZ_Ok