Female fertility: air pollution and ovaries

Now they say it takes two to tango, and fertility has both male and female factors. Cambridge University obstetrician and researcher Catherine Aiken spoke to Chris Smith about the female side of fertility...

Chris - Catherine, I suppose that the pandemic must have had an impact in and of itself on fertility rates, because of people choosing to defer whether or not they have a child, because of concern around what might happen?

Catherine - Yes, absolutely. So at the start of the COVID pandemic, everyone was talking about a baby boom. It now looks much more like COVID's going to produce a baby bust. Having said that, at Addenbrooke's and Cambridge we certainly haven't seen an empty labour ward; in fact, we seem to be busier than ever. But we are hearing reports from hospitals that are just emerging that there are now fewer pregnancy dating scans being done, so fewer people booking for pregnancies; and there are also several large surveys that suggest people are delaying pregnancies, as you say, due to financial concerns: particularly rising unemployment, but also they cite direct health fears about COVID. And interestingly, the lack of their usual social networks and support seem to be really concerning people. And all of them seem to be contributing to fewer rather than more pregnancies this year.

Chris - Do people in reality have anything to worry about? As in, if they do fall pregnant while they are experiencing this... the pandemic situation, and were they to catch coronavirus infection while pregnant, what do the data say about the likely outcomes?

Catherine - What we know is that when women are pregnant, they are slightly more susceptible to the severe outcomes of COVID than when they aren't. And that's true for many viral illnesses, such as flu for example. We are very good at treating that, we're very good at picking it up early, and the healthcare system is very aware of it at the moment, but certainly COVID infection during pregnancy has been linked with preterm birth, reduced growth of the baby inside the womb, and more severe outcomes for mum overall. We know that COVID doesn't seem to transmit readily across placentas, but the effect on the mum can certainly have knock on effects on babies. But I would emphasise that being pregnant at the minute really is, in general, not a dangerous thing, and that we're good at dealing with that when it does occur.

Chris - And are there any documented impacts on fertility, having caught COVID? Because we've heard in recent weeks about the possible impact on male fertility, and perhaps we'll hear a bit more about that when we talk to our next guest in a moment, but is there any evidence that catching coronavirus can affect an ability of a woman to reproduce?

Catherine - We really don't have any good evidence that COVID directly impacts female fertility. Now, clearly there may be indirect impacts: for example, increased anxiety and stress can certainly reduce the chances of conception. There's also factors like increased weight gain and less healthy lifestyles during lockdown that may well be impacting on fertility. And certainly there was reduced access to fertility treatment, particularly in the early stages of the pandemic when many IVF clinics and so on closed their doors. And there are theoretical concerns: the binding receptors for COVID, which it needs to get into cells, are expressed in the female reproductive tract. But there really isn't any strong evidence that this is actually clinically significant in reducing female fertility.

Chris - Well, there's some reassurance there then. Based on what you did say though, that there are other factors that we do know are linked, do you think that they account for the decline in fertility that we've seen: the numbers I cited at the beginning of the programme, an apparently quite dramatic reduction in the rate of reproduction in women in America between just 2006 and 2020. Things like weight gain, things like diet, exercise, smoking - can we account for this reduction in fertility in those terms?

Catherine - I think we can account for a large part of it, yeah, I really do. I think as Brianna said, maternal age is the absolute key driver more than anything else. And we know that since 2013, the average age of women giving birth in the UK has been well above 30, which means a reduction in egg quality or a reduction in egg number, and that does just have an impact on population fertility. But obesity's also a big influence on reproductive health, and one in five women who books a pregnancy in the UK at the moment is obese at the start of pregnancy. One in eight women is a current smoker during pregnancy in the UK at the moment. And then in global terms, there are many more interesting factors; some linked with climate change, some linked with endocrine disruptors, ,and the impact of air pollution.

Chris - Well, we'll return to this question of endocrine disruptors, things coming from the environment that can mimic the body's own hormones... we're going to talk to Paul Fowler later in the program about that, he's actually been looking specifically at that. But air pollution is a big one as well, isn't it? This is something which we know is getting worse and worse and worse, and is very strongly linked to rate of mortality; but could it also be impacting on fertility then?

Catherine - Well, there certainly are plausible observational studies that link ambient air pollution to both longer times to spontaneous conception and to less successful fertility treatment. There are some good rodent studies that show that there are plausible mechanisms that link that. Because eggs stay in this arrested development stage for so long, the DNA is uniquely sensitive to external influences, and we know that air pollution particles can reach the ovaries. Air pollution might also affect transport of eggs and sperm, but I think what I'd emphasise is that the majority of human studies in this space are very observational, we don't have any good quality prospective studies, and we really need to know more about how in practice, the health of women, the reproductive health of women who live in high pollution areas is impacted.