Now, I don’t know about you, but I don’t remember much from my sex education at school. What I do remember is some labelling of anatomy diagrams and our biology teacher trying to explain periods, getting flustered and mumbling something about making sure we disposed of our pads properly in the bin. Suffice it to say I’ve learnt a lot about my own bloody body in the past few years which I am fairly sure I should have already known. However, in talking to friends it appears I am not the only one with substandard knowledge of reproduction and the reproductive system, so buckle up as I’m going to attempt to explain in my idiots guide to making babies. Enjoy.
(Note, I am {obviously} not a doctor and nor do I have any knowledge of biology beyond year 9 so the following is garnered from what I have read over the past few years)
Right, lets start with the basics of the female menstrual cycle before we talk about it in the context of fertility treatments.
The accepted norm for a female menstrual cycle is 28 days. This is made up of the first 14 days called the follicular phase and the second 14 called the lutuel phase (aside: it’s a game of 2 halves! Surely this should make it easier to explain??). In the middle of these two ovulation occurs. Now obviously not everyone has 28 day cycles, or ovulates on day 14, especially if you have conditions like PCOS (Polycycstic ovaries syndrome) or a lutuel phase defect, but I digress.
What happens in the follicular phase? The clue is in the name – during this stage the follicles in the ovary are growing. In someone at peak fertily anything from 10-20 follicles will be in the ‘race’ at the start of this phase – this phase starts from day 1 which is also the first day of proper bleeding – so you’re menstruating but your body is already gearing up for another go.
After some time one follicle becomes dominant and the others stop developing and ‘die back’ (this is not the proper term, but I’m a gardener at heart, so sue me). This is the follicle and egg that the body has decided has the best chance to make a baby this month. A follicle will grow to about the size of a grape, and the ovary is about the size of a walnut (and floats freely in the body which means it can twist and get starved of blood supply – honestly the things you learn). Remember these relative sizes when we come to talk about IVF.
A couple of days before ovulation a womans basal body temperature (BBT) will start to drop as the body gears up to release the egg. At the same time (warning – potential tmi following…) cervical mucus changes until around ovulation it resembles egg white in consistency and colour (people post photos of this on fertility chat boards, no really, they do 🤮). These are also acidic hence why you ruin your pants… (Seriously, this would have been soooo good to know years ago 🙄).
Anyway, so you ovulate – hurrah! Your egg will survive for 12-24 hours maximum. In contrast mens sperm can last anything up to 10 days (10days!!! 😱) in the uterus, although the accepted figure is around 5-6days. Pregnancy rates are highest when sex takes places 2-3 days before ovulation – it’s a long swim and they’re only little. Yes. Everyone’s. This is where you will also hear things like male sperm swims faster than female sperm so if you want a girl have sex before ovulation and for a boy on the day of – aka, male sperm are fast but die off quicker, female sperm are slower but last longer… TBH this is probably bollocks though.
So, all you have to do is hit ovulation day right? Day 14, mark it in your diaries and jobs a good ‘un? Yeah, no. Depending on age your potential success rate each month ranges from 25% down to 1-2% in your mid-late 40s. This is because you are born with all the eggs you will ever have and as you age you’ve released more of the good ones – basically older eggs are more likely to be chromosomaally abnormal – up to 90% for a woman in her 40s.
Anyway, so you’ve released an egg and it’s met some sperm and fertilised, whoop! Highway to parenthood surely? Erm, nope. About 50% of fertilised eggs are passed out during your period – they never make it to implantation.
So the egg is fertilised, it’s now an oocyte. As it develops, splitting into more and more cells it becomes an embryo. Whilst this is happening it’s travelling down the fallopian tubes from the ovary towards to uterus.
After about 5/6 days it’s now developed from an embryo into a morula and then a blastocyst and ‘hatched’ from its shell (yes, apparently, we have something in common with chickens). Between 6-12 days post ovulation implantation happens. This is when the blastocyst burrows (😱) its way into the endometrium where it will hopefully stay for the next 38-42 weeks. Congratulations, you are now pregnant.
If that doesn’t happen, you can expect your period to arrive on day 28. Because implantation can happen between day 20 and 26 (6 to 12 days after ovulation) this is why some pregnancy tests can give you the correct result even before you miss your period – well, the more sensitive ones anyway. Pregnancy tests react to human growth hormone (hcg) which starts being produced as soon as the embryo implants. HCG then starts to double every few days as the pregnancy develops. If this doesn’t happen it can be an early indication of impending miscarriage.
Right then, so that’s what happens in a natural cycle, what happens in IVF? Follow me to another blog I already wrote to find out: https://every-day.blog/wtf-is-ivf-anyway/