A basal temperature implantation dip cannot tell anyone whether a transfer has worked. In the largest chart analysis, the one day dip turned up on only 1.6 per cent of more than 1.5 million charts, pregnant and not pregnant alike. After IVF, prescribed progesterone holds the temperature up, so the chart largely follows the medication.
Listen to this article, about 10 minutes. A synthetic voice reads the article and announces each section title as it begins; tables are read row by row and the questions at the end are left out.
Recorded 8 October 2026 from the article as published that day. Press a chapter to jump there; the highlighted line is what is playing. A play button sits beside every section heading, and once you scroll past this player a bar at the bottom of the screen keeps the controls in reach. Tap or click any sentence to hear the reading start from there.
On this page: what the 1.5 million chart implantation dip analysis really reports, a table of where the progesterone comes from in each type of transfer cycle, a 2025 study showing temperature tracks progesterone, and three forum accounts from people who charted through IVF.
Think you already know this? Five questions, one minute.
Every answer is on this page. Answer from what you know now; the page fills in the rest.
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1. Why does basal temperature normally rise after ovulation?
Progesterone from the corpus luteum raises basal temperature by an estimated 0.5 to 1 degree Fahrenheit (StatPearls review). Read the section
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2. In Fertility Friend’s analysis of more than 1.5 million charts, what share showed the one day implantation dip?
The dip appeared on 1.6 per cent of all charts; 79.8 per cent is a relative comparison between groups, not a share of charts (Fertility Friend analysis). Read the section
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3. In the 2025 study of 18 patients in hormone assisted transfer cycles, what did overnight temperature track?
The study found a strong relationship between overnight temperature and blood progesterone, best matched by the previous night’s reading (Knowles and colleagues, 2025). Read the section
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4. In the 1977 study of 60 charts, for roughly what share was the day of ovulation predicted correctly?
About 80 per cent were sorted correctly as ovulatory or not, but the day itself was right for only about 34 per cent (Lenton, Weston and Cooke, 1977). Read the section
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5. At what reading does the NHS define a high temperature in adults?
The NHS defines a high temperature as 38C or above, and notes someone feeling hot or shivery may have one below that (NHS high temperature in adults). Read the section
What is the implantation dip on a basal temperature chart?
Basal body temperature is your resting temperature, taken first thing in the morning before you sit up, talk or reach for the kettle. In a natural cycle it runs lower before ovulation and then steps up afterwards, because progesterone from the corpus luteum, the small gland left behind when an egg is released, nudges the body’s thermostat upwards. The StatPearls review of ovulation and basal body temperature puts that rise at an estimated 0.5 to 1 degree Fahrenheit, roughly 0.3 to 0.6 degrees Celsius.
The implantation dip is the idea that, a week or so after ovulation, the temperature drops for a single day and then climbs back up, and that this drop marks the embryo settling in. It is a tidy story. It also lines up nicely with the timing of implantation itself: in the classic urine study by Wilcox, Baird and Weinberg in the New England Journal of Medicine in 1999, hCG first appeared 6 to 12 days after ovulation. Lining up nicely is not the same as being caused by it, and that gap is what the rest of this page is about.
Our page on what the evidence says about signs of implantation after transfer covers the wider symptom list. Here the question is narrower: what do the numbers say about this one squiggle on a chart?
What does the largest chart analysis actually show?
The figure that the dip pages lean on comes from the charting service Fertility Friend, which has published an implantation dip analysis of more than 1.5 million charts. It defines the dip strictly, as a significant one day drop between 5 and 12 days past ovulation. Three numbers matter, and the first one rarely makes it into the headlines.
| What the analysis reports | The figure | What it does and does not mean |
|---|---|---|
| Charts showing the dip at all | 1.6 per cent | Roughly 1 chart in 60. Most charts, pregnant or not, never show it. |
| How much more often it appears on pregnancy charts | 79.8 per cent more likely | A comparison between two groups, not a 79.8 per cent chance of anything. |
| Average day of the dip on pregnancy charts | 8.6 days past ovulation | Close to when implantation is thought to happen, which is where the story comes from. |
| Does the dip appear on non pregnancy charts? | Yes | The service says plainly that the pattern does not necessarily mean pregnancy. |
That 79.8 per cent is the number that gets passed around, and it is easy to misread at two in the morning. It is a relative comparison: a pattern that is rare in one group and rarer still in another can be “79.8 per cent more likely” in the first while still being absent from almost all of both. The analysis does not say what share of pregnant charts had a dip, so nobody can work backwards from it to the odds for one chart.
The other quiet detail is who was charting: people tracking natural cycles. Nothing in the analysis says it included IVF, and an IVF chart measures something rather different.
Why does progesterone after a transfer change the chart?
After an embryo transfer, most clinics prescribe progesterone to support the lining of the womb. The European fertility society’s ovarian stimulation guideline strongly recommends progesterone as luteal phase support after IVF, so this is standard practice rather than an unusual extra. Which product, which route and for how long is a decision for each clinic, and this page does not go near it.
Here is why that matters for the chart. In a medicated frozen transfer, the cycle is built with hormones and no egg is released, so there is no corpus luteum at all; a 2024 review of luteal support in embryo transfer cycles describes the progesterone in those cycles as coming entirely from the prescription. In a fresh cycle the ovaries are also recovering from stimulation and producing their own. Either way, the hormone that raises basal temperature is partly or wholly arriving by prescription. Our comparison of medicated and natural frozen transfer cycles explains the cycle types in more detail.
There is now a direct measurement of this. In a study published in February 2025, Knowles and colleagues monitored overnight temperature in 18 patients having hormone assisted embryo transfer cycles at clinics in Spain, using a vaginal sensor, and compared it with blood progesterone. They found a strong relationship between the two, with the best match coming from the previous night’s temperature. In other words, the temperature tracked the progesterone level. It was a small study with a dedicated sensor rather than a bedside thermometer, but the point stands: what moves the line is the hormone in the bloodstream.
| Type of cycle | Where the progesterone comes from | What a high reading mostly reflects |
|---|---|---|
| Natural cycle, no treatment | The corpus luteum after ovulation | That ovulation happened |
| Fresh IVF transfer | The ovaries after egg collection, plus prescribed progesterone | Both sources together |
| Medicated frozen transfer | Prescribed progesterone only; no corpus luteum forms | The medication |
| Natural or modified natural frozen transfer | The cycle’s own corpus luteum, sometimes with added progesterone | Ovulation, plus any added progesterone |
So a high, steady chart after a transfer is mostly a record of a medicine doing its job. A one day drop can follow a restless night, a cold bedroom, a reading taken an hour late or the timing of a dose. None of those is a message from the embryo, and none of them is a reason to change anything the clinic has prescribed.
How reliable was a temperature chart even before IVF?
Basal temperature charts have a modest record even for the job they were designed for, which is spotting ovulation after the fact. In a study in the British Medical Journal in 1977, Lenton, Weston and Cooke gave 60 temperature charts to gynaecologists and to non experts. Both groups sorted about 80 per cent correctly into cycles that did or did not ovulate. But the day of ovulation was predicted correctly for only about 34 per cent of the charts, and the lowest point on the chart lined up with the hormone surge in 43 per cent of normal cycles and 25 per cent of those from the infertility clinic.
The authors concluded that predicting the day of ovulation from a temperature chart was unjustified, especially in women with fertility problems. That is a tool struggling to pin down a large hormonal event. Asking it to spot an embryo attaching, through a fog of prescribed hormones, is asking a lot of a thermometer from the chemist’s.
What do people who took their temperature after transfer report?
We read three accounts from people who took their basal temperature during or after IVF, on Mumsnet and the Canadian forum IVF.ca. Three is a small number, and these are what people report, not findings.
In a Mumsnet thread started in November 2021, a poster five days after a day five transfer noticed a higher than usual morning reading and felt encouraged, then remembered that the progesterone they were taking raises temperature on its own. The thread does not say how that cycle ended, which is fitting, because the reading could not have said either.
On an older IVF.ca thread, from around 2010 going by the dates on the page, one poster described charting through several IVF cycles. Temperatures swung up and down in every cycle, including a pattern they had read as hopeful in a cycle that ended negative, and the same wild swings in a later cycle that ended positive. Their conclusion was that the hormones made temping impossible to rely on.
A reply on another IVF.ca thread from the same era ran the other way. A long time charter skipped temping during IVF, took a reading after a positive test, and found it back at their pre ovulation level. They describe a frightened phone call to their doctor, who told them not to worry about the thermometer.
Where the accounts agree with the evidence: the temperature moved with the medication and did not sort good news from bad. Where they cannot help: none of them is a guide to what a chart means for anyone else. People whose charts did nothing remarkable rarely post at all, the same silence we describe in why having no symptoms is not evidence either way.
When is a temperature reading a reason to call the clinic?
Basal temperature and fever are different things. A basal reading sits in a narrow resting range and moves by fractions of a degree. A fever is something else: the NHS defines a high temperature in adults as 38C or above, and notes that someone who feels hot, cold or shivery may have a high temperature even if a thermometer reads below that.
If you have a temperature of 38C or above after an embryo transfer, or feel feverish and unwell, call your clinic or NHS 111 the same day. Do the same for heavy bleeding, severe pain, breathlessness or a swollen, painful leg. Do not stop or change any medication because of a chart. Your clinic knows your protocol and your test date; this page does not.
For everything else, the honest answer is the unsatisfying one: the result comes from the blood test on the date your clinic gave you. Our guide to testing at home after IVF explains why early tests mislead too, and the implantation timeline after a day 3 or day 5 transfer sets out when each step happens. Putting the thermometer in a drawer is not giving up. It is declining to let a medicine’s side effect narrate your fortnight.
This page is general information, not personal medical advice. Speak to your fertility clinic or another qualified professional about your own treatment and symptoms.
Two week wait clinic log
A private note of dates and what your clinic told you, kept in this browser only. It records what was said; it does not read anything into it.
Questions about your medication or symptoms belong with your clinic, which knows your protocol.
Frequently asked questions
Does a high temperature after embryo transfer mean pregnancy?
No. After a transfer, prescribed progesterone raises basal temperature whatever the outcome, and a 2025 study found overnight temperature tracked blood progesterone in medicated transfer cycles. A high chart mostly reflects the medication.
Does a temperature drop after transfer mean it has failed?
No. A one day drop has ordinary causes, such as a poor night, a cold room or a late reading, and the dip pattern appears on pregnant and non pregnant charts alike. It cannot be read either way.
How many people actually see an implantation dip?
In Fertility Friend’s analysis of more than 1.5 million charts, the strictly defined one day dip appeared on 1.6 per cent of charts. Most charts, including pregnancy charts, never show one.
When is the implantation dip supposed to happen?
Fertility Friend looks for it between 5 and 12 days past ovulation, and reports an average of 8.6 days on pregnancy charts. That overlaps with the timing of implantation, which is how the idea took hold.
Why is basal temperature higher on progesterone?
Progesterone acts on the part of the brain that sets body temperature and shifts it upwards. The StatPearls review puts the natural rise after ovulation at about 0.5 to 1 degree Fahrenheit.
Is it harmful to chart temperature during the two week wait?
Charting itself is not harmful, but it cannot answer the question it is usually used for. Many people find it adds worry. Your clinic’s blood test date is when the result is known.
Finished the page? The same five questions from the top, to see what stuck.
This article is general information, not medical advice, and is not a substitute for care from a qualified healthcare professional. Speak to your doctor about your own situation.
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