Why can fertile people struggle to conceive?

Lindsay posted this question about fertility and compatibility on the forum. Izzie Clarke asked reproductive physiologist Bill Colledge to explain why some fertile couples struggle to conceive.

Bill - Occasionally this does happen. I think one of the reasons is that fertility can be affected by a huge range of different factors. So you might have a couple where they're both slightly subfertile so that together that's a compound problem - they can't conceive. And then if they split up and they find another partner, the new partner is completely fertile and their subfertility isn't such a problem, so that's one of the possible reasons.

Another reason is that in very rare conditions, maybe about 4% of the time, it is known that a woman can make antibodies that will specifically recognise the partner's sperm. So they make antibodies which are released into the vagina when they have sex, the sperm are attacked by the antibodies and it causes the sperm to clump and coagulate and that prevents the sperm from reaching the egg.

Izzie - And so essentially they are rejecting it?

Bill - They are rejecting it, yes. I mean I don't think that they have been primed against it or anything like that, it's just that there's this incompatibility which is unfortunate for that particular couple.

Izzie - Would there be anything to get around that issue?

Bill - Oh, yes. There are ways of getting around that if that is the problem. You can obviously take the egg from the woman and you can fertilise it using in-vitro fertilisation in a dish, and then you can take the fertilised egg and you can implant it back in the woman. That means that there's no antibodies in the dish so it should work fine.

Izzie - And Kit, did you have a question?

工具-是的。我很好奇是否someone would be attacking every sperm, or is it just a specific person’s sperm, or is it a specific group of people's sperm?

Bill - It's related to a person's sperm. So if they have this problem that they make antibodies against a particular sperm, it'll be all of the sperm from that person and it necessarily won't be from another person, so it's not selective, it'll be all of the sperm that are attacked.

Izzie - And how important are hormones when it comes to fertility?

Bill - Hormones are very important in fertility. In males, for example, testosterone is absolutely crucial for fertility. When you go through puberty, your testosterone level rises and that's required to start making sperm at puberty. And anything that reduces your testosterone after puberty is going to impact on your ability to make sperm and there are a lot things that could impact on your testosterone levels. One thing is that if you are overweight and you have a lot of fat tissue, then testosterone is lipophilic, it likes lipids, which fat tissue is, it'll tend to get sequestered into the fat tissue which can result in lower levels of testosterone in the bloodstream which can have an effect on how well you make sperm.

Izzie - I see. Now Howard, how about plants? What determines how many seeds a plant makes?

Howard - Oh, well. That's a big question. Well, it depends what sort of flower it makes. Sometimes plants make a single flower if they have a kind of determinate structure, what we call their inflorescence. Sometimes when they start flowering at the bottom and they just keep flowering, like wallflowers at the moment, that's just called indeterminant so they can have lots and lots of seed pods and so on. That's partly the condition.

It also depends on whether they've got enough water and nutrients. Plants can adjust their structure, the number of branches they might have, the number and size of the flowers they have, if they've got plenty of resources and that's all controlled by similar substances to the animal hormones - we call them plant growth substances.

And then finally, it decides whether they need to allocate reproductive effort into seeds or sometimes you might have other storage organs. So take the potato for instance, we know that they store a lot of resources underground because they reproduce from that vegetative structure. It depends really how you're going to produce your generation in the following year, whether it's from a seed or whether it's from a vegetative structure.