I was wearing Oura, Whoop & Apple Watch when I got pregnant.
That was how Dr Sian Allen started this fascinating thread on Twitter, further below. No doubt as she continues her 9-month journey more HRV insights will follow.
Background: Dr Allen is a regular and informed HRV tweeter and one of the ones to follow if you are interested in sports/HRV and already know what rMSSD means.
CONCLUSION Body temperature from Oura was the best leading indicator of early pregnancy detection.

Technical Background
Many health and wellness technologies for consumers provide insights and analyses around fertility cycles. To varying degrees the key players, Apple, Oura, Fitbit, Whoop and Garmin use body temperature, resting heart rate and resting HRV in their algorithms. Other data points are also used. For example, I always thought that (optionally!) logging my sexual activity in Whoop was a little intrusive, I’m not sure why because no one else could see it apart from me. But that’s how it felt. Dr Allen seems to have taken this to a whole new level and uses some of our favourite tech to record the moment of conception.
This post could now go down numerous avenues but let’s just end it and say congratulations to Dr Allen and her partner!
PS I’m not entirely sure if that picture, above, is appropriate or not. It’s from FitGear Hunter’s YouTube channel and he did some work with me on the Whoop Review, but Hunter looks excited enough about the news too 😉
Must Read: Whoop Review
Must Read: Apple Watch 7 Review
Here is the Twitter thread with data, it should also show up below!
HRV
Clear trend for ⬇️ HRV from all 3 devices in the weeks following conception.
The sharpest drop was in my Oura values.
Similar to resting HR – I initially put these changes down to an increased stress response from returning to training. pic.twitter.com/X0TvIxXhZ8
— Sian Allen (@DrSianAllen) February 2, 2022
APPLE DATA
Resting HR from Apple was trending up around this time.
And HRV trending down in general.
At the time these changes looked like explainable natural variation and didn't signal anything else worth looking into… pic.twitter.com/y7DQ6330j4
— Sian Allen (@DrSianAllen) February 2, 2022
WHOOP DATA
I had more red recovery scores from Whoop than usual.
But these rebounded up to yellow and green when I reduced my training load (⬇️ strain, Mar 21-24).
So I assumed red was a slow response to resuming training, like with my resting HR and HRV data… pic.twitter.com/nygVkOOM95
— Sian Allen (@DrSianAllen) February 2, 2022
OURA DATA@ouraring's temperature data was the best indicator that I was pregnant by miles.
I've never seen this kind of sustained temperature increase with illness, training response, or anything else going on. pic.twitter.com/pVjymQ9Aen
— Sian Allen (@DrSianAllen) February 2, 2022
SUPPORTING RESEARCH
A UCSD study found Oura's temperature data may be a viable tool for passive, early pregnancy detection:
On average, 5.5 days after conception
All 30 people studied showed clear ⬆️ in body temperature around conception.https://t.co/RdbNa99d8r pic.twitter.com/wXpl5jfxuM
— Sian Allen (@DrSianAllen) February 2, 2022
CONCLUSION
Body temperature from @ouraring was the best leading indicator of early pregnancy detection…
…weeks before I took a test!
In hindsight, I can see it in my HR & HRV trends from Whoop and Apple. But at the time, I misattributed these to changes in training load.
— Sian Allen (@DrSianAllen) February 2, 2022