The WRISK project regularly asks contributors to share their perspectives on a range of issues related to risk communication in pregnancy to further understanding of the challenges faced by scientists, clinicians, policy makers, and of course women themselves when trying to navigate risk messaging. These represent individual and personal viewpoints, and are aimed at encouraging reflection and discussion, rather than reaching conclusions.

In this blog, Katy Lindemann explores a controversial new study from researchers at the University of Leiden, published in the Journal of Reproductive Immunology.  Katy is writer-in-residence at @FertilityFest and the founder of the Uber Barrens Club. She is currently writing a book about the reality of infertility and pregnancy loss, and tweets at @uberbarrensclub.




Is this for real?

Yes. Although I first assumed this must have been an April fool, it’s actually a genuine study from researchers at the University of Leiden, published in the Journal of Reproductive Immunology.

Behind the clickbait headlines, the basic premise of the study isn’t quite as far-fetched as it sounds:

  • The theory is that regular exposure to her partner’s semen primes the woman’s body to recognise the fetus, so it’s less likely to mount an immunological attack on the baby.
  • Previous research has focused on vaginal exposure — several studies have suggested that unprotected vaginal sex around the time of embryo transfer could increase the likelihood of successful early embryo implantation and development.


Er, but what’s oral sex got to do with it?

The authors’ hypothesis is that oral exposure to the antigens in semen may be effective due to superior absorption in the gut.

However there might be a few holes in this theory  — as immunologist Dr Angharad Watson points out:


Although a 2000 study (also conducted by researchers at the University of Leiden) suggested that swallowing sperm was correlated with a diminished occurrence of preeclampsia, a 2014 study found that oral exposure to semen made no difference at all.


OK, so what did this study actually say?

What they did: they asked 97 women who’d had multiple miscarriages, and 137 women who’d had none, to complete a questionnaire about their general medical history and sexual behaviour—including questions about how often they had oral sex and whether they swallowed the ejaculate.

What they found: 


Side note: nice bit of misogyny 

  • At no point in the study is the term ‘oral sex’ defined as referring specifically to fellatio.
  • The authors don’t seem to have considered that women “having oral sex” could also refer to women “receiving oral sex”.
  • Or that “having oral sex” doesn’t automatically involve swallowing semen.


Problem 1: The study’s methodology is flawed

Here’s what the experts had to say:

Dr Angela Lawson, Associate Professor of Clinical Obstetrics & Gynaecology and Psychiatry, Northwestern University Feinberg School of Medicine:


Dr. Lora Shahine, Reproductive Endocrinologist; clinical faculty member of the department of OBGYN at the University of Washington; director of the Recurrent Pregnancy Loss Centre at Pacific NW Fertility:


Prof Joyce Harper, Director of Education, Head of the Department of Reproductive Health and Director of the Centre for Human Reproduction at the Institute for Women’s Health at University College London:


Noortje Uphoff, Epidemiologist; Research Fellow at the Centre for Reviews and Dissemination, University of York:


Dr Matt Prior, Consultant in Reproductive Medicine, Newcastle Upon Tyne Hospitals Trust; leader of the Miscarriage Priority Setting Partnership:


For a more detailed critique, the American Council on Science and Health have also helpfully published a comprehensive analysis of the study’s shortcomings — of which there are many.

The expert verdict: 0/10 —completely unreliable.


Problem 2: The study’s findings are unreliable

What they said they found: “Oral sex seems to influence pregnancy outcome in a proportion of the women”

What they actually found: Nothing.


Correlation does not equal causation

The authors note an association between fellatio and miscarriage. The women who’d suffered recurrent miscarriage performed oral sex less often than the women who hadn’t. 

That doesn’t mean there’s any causal link. 

There are a million and one other variables that could account for this higher rate of miscarriage — one spurious correlation doesn’t actually tell you anything.


You can find correlations between pretty much anything — it doesn’t mean they’re connected:

Beware of spurious correlations

Problem 3: The authors confuse cause and effect

‘Non-miscarrying women give more blow jobs’ doesn’t necessarily mean that giving blow jobs reduces the likelihood of miscarriages.

Here’s a radical thought. Might it be that the emotional trauma of recurrent miscarriage might affect a couple’s sex life?

Maybe, just maybe, for these women their every waking minute was filled with dread about miscarrying again — which amazingly might not have got them in the mood for lots of blow jobs? Maybe their losses had also affected their partners’ libidos? (Because despite what this study might suggest, miscarriage involves both partners — not everything is always down to the woman).

Could it possibly be that the difference in frequency of oral sex was a consequence of miscarriage, rather than a cause?


Problem 4: There might not actually be any correlation at all

More than half of the women didn’t even complete the questionnaire — including questions about their sex lives.

“We were confronted with incomplete data from questionnaires, especially missing data on sexual behaviour, which was our exposure of interest.”

Right. So incomplete data pertaining to the specific issue that’s the premise of the study. That sounds promising.

To try and fix the problem, the the authors ‘imputed’ replacement data (ie they guessed what the missing data should have been),

Once they’d adjusted the data the correlation between oral sex and miscarriage disappeared entirely.


In summary:

  • The study’s title and key claims are misleading.
  • There is zero indication that the frequency of sperm consumption has any bearing on the risk of miscarriage whatsoever.
  • The study adds nothing to our understanding of what causes miscarriages.


This isn’t just problematic, but emotionally harmful

After a miscarriage, women are often quick to blame ourselves — I know I certainly did after mine.

Believing that it’s our fault. That we’re somehow responsible. That we did something wrong.That we could have prevented it.

These feelings of guilt and shame are exacerbated by misconceptions about what might have caused our losses —and this study gives us another stick to beat ourselves with.

That if only we’d given more blow jobs, we might not have lost our babies.

Infertility and miscarriage can have a devastating effect on intimacy in a couple’s relationship, and articles like this may only worsen this.

After I posted about this study on Twitter and Instagram, I received a flood of comments and messages from women who found these stories really, really hurtful. Many remarked that they hoped their husbands wouldn’t see any of these headlines in case it gave them any ideas!

Although these comments were said lightly in jest, they belie a more sinister truth. That because of these articles, many women may feel pressured to perform sex acts out of a sense of obligation— perhaps even under coercion from partners using this as an excuse to demand more oral sex.

As one woman on Twitter put it:

“I had recurrent miscarriages and GUESS WHAT I DIDN’T FEEL LIKE SUCKING D**K. If only I’d known about this totally legitimate research I would have performed a sex act I didn’t want to do, out of guilt. And still miscarried. Because giving head doesn’t save babies”

Articles like this illustrate perfectly why the WRISK project is so very much needed. The outcome of the project is the development of “recommendations for respectful risk communication in pregnancy” —respect that was sorely missing here.