Most side effects during egg freezing are mild and expected, a predictable result of a two-week hormone shift rather than a sign something has gone wrong. A small number are serious enough to need same-day medical attention. Knowing the difference in advance makes the whole process considerably less anxiety-inducing, and gives you a clear frame of reference to work from rather than second-guessing every new sensation as it comes up.
Common and expected, during stimulation
Mild bruising and soreness at injection sites, bloating and breast tenderness, nausea, fatigue, mood swings, increased vaginal discharge, and occasional temporary skin reactions at the injection site are all common during the stimulation phase (Cofertility, 2026). See our guide to what the injections actually feel like for more on the day-to-day experience of this phase. None of these need a phone call; they are a normal part of the hormonal shift that stimulation medication causes, and most settle on their own once stimulation ends and retrieval has taken place. It is worth knowing in advance that several of these, particularly bloating and breast tenderness, tend to build gradually across the stimulation window as follicles develop, and are often most noticeable in the final few days before retrieval, which is a useful thing to expect rather than be surprised by.
Common and expected, around retrieval
In the day or two after the retrieval procedure, mild constipation, bloating, cramping and light spotting are all common, alongside some soreness from the procedure itself. Our day-by-day cycle timeline covers where retrieval sits in the wider process. These generally ease within a few days, though mild bloating in particular can persist a little longer for some women, especially if a larger number of follicles developed during stimulation. Rest, hydration, and following any specific aftercare advice your clinic gives you are usually all that is needed while these symptoms settle on their own.
OHSS: the main thing to actually watch for
Ovarian Hyperstimulation Syndrome (OHSS) is the primary medication-related risk worth understanding in detail. It happens when the ovaries respond more strongly than expected to stimulation medication and become swollen and painful. Severe OHSS is uncommon, estimated to occur in roughly 0.1 to 2% of cycles, and clinics actively work to prevent it through careful monitoring and dose adjustment throughout your stimulation days (Cofertility, 2026). This is exactly why those repeated scans and blood tests matter, even when they feel like a lot of appointments in a short space of time; they are how your clinic catches an overly strong response early enough to adjust your protocol before it becomes a genuine problem.
Mild OHSS, distinct from the severe form, is considerably more common and generally involves bloating, mild abdominal discomfort and nausea that resolves within a week or so without specific treatment beyond rest and monitoring. It is worth understanding this distinction, since mild OHSS symptoms can overlap with the ordinary, expected side effects of stimulation listed above, which is part of why clinics ask you to flag anything that feels notably worse than you were told to expect, rather than trying to self-diagnose which category a symptom falls into.
Who is more likely to experience OHSS, and why it is monitored so closely
Certain factors increase the likelihood of a stronger ovarian response, including a higher antral follicle count, polycystic ovary syndrome, and younger age, since younger ovaries often respond more vigorously to the same medication dose than older ones do. If any of these apply to you, your clinic will typically factor this into your starting dose and monitoring schedule from the outset, sometimes using a lower starting dose or an alternative trigger medication specifically to reduce OHSS risk. This is one of the clearest examples of why a personalised protocol, built around your own AMH, AFC and medical history, matters more than a standardised one-size-fits-all approach to stimulation.
Rarer retrieval-related risks
Beyond the anaesthesia itself, which carries its own standard, small risks your clinic will talk you through in advance, acute complications from the retrieval procedure, such as infection or internal bleeding, occur in under 0.5% of cycles (CUH NHS Foundation Trust, 2026). Clinics take specific precautions to minimise these risks, including sterile technique during the procedure and clear aftercare instructions covering signs of infection to watch for in the days that follow.
Call your clinic immediately if you experience
A fever above 38.3 degrees Celsius (101 degrees Fahrenheit); severe abdominal pain that does not respond to over-the-counter pain relief; persistent, severe nausea or vomiting; heavy vaginal bleeding, defined as soaking a pad within an hour; difficulty urinating; or fainting or significant dizziness. Clinics would always rather hear from you and rule something out than have you wait it out at home, and calling with a symptom that turns out to be nothing is never treated as an overreaction.
How to tell ordinary discomfort from something worth flagging
A useful, general rule many clinics suggest is to think in terms of trajectory rather than a single moment: ordinary side effects tend to plateau or gradually improve day to day, while something that needs attention tends to get noticeably worse rather than better, or arrives suddenly and intensely rather than building gradually. Trust that shift in trajectory as much as the specific symptom itself. If something feels different from what you were told to expect, whether or not it appears on either list above, it is always reasonable to call and ask, and clinics genuinely prefer this to patients trying to reason their way through uncertainty alone.
If OHSS does develop, what happens next
If your clinic identifies signs of a strong ovarian response during monitoring, the first response is usually a protocol adjustment rather than immediate intervention, such as lowering your medication dose, changing your trigger medication to one associated with a lower OHSS risk, or, in some cases, recommending that all resulting embryos or eggs be frozen with no fresh transfer planned, removing pregnancy-related hormone changes that can otherwise worsen OHSS. For confirmed mild to moderate OHSS after retrieval, management typically focuses on rest, hydration, monitoring fluid balance, and pain relief, with most cases resolving within one to two weeks without further intervention. Severe OHSS is managed more closely, sometimes requiring hospital admission for fluid management and monitoring, though this remains uncommon precisely because of how closely clinics track response throughout stimulation. Knowing that a clear management pathway exists, rather than assuming OHSS is an unpredictable emergency with no plan attached, tends to make the whole topic considerably less frightening to read about in advance.
Emotional side effects, and why they deserve equal attention
Alongside the physical symptoms above, it is worth naming the emotional side of a stimulation cycle directly, since it is just as real and just as commonly reported. Heightened sensitivity, low mood, irritability and a general sense of being more emotionally reactive than usual are widely reported during stimulation, driven by the same hormone shifts responsible for the physical symptoms. For some women, the retrieval and the wait that follows also bring up feelings about the broader decision to freeze, unrelated to the medication itself, and both are entirely normal responses to a process that is, however routine for a clinic, a significant personal experience. Most clinics can point patients toward counselling support if the emotional side of a cycle feels heavier than expected, and asking about this option is treated the same way as asking about a physical symptom, as a normal, expected part of good care rather than an unusual request. Bringing a trusted friend or partner to appointments where major decisions are discussed can also help, since it gives you a second set of ears on information delivered during what is often an emotionally charged stretch of time, and someone to talk it through with afterward once the appointment itself is over.
Looking after yourself day to day during stimulation
Alongside knowing what to watch for, a few simple habits tend to make the stimulation window more comfortable. Staying well hydrated, eating regularly even when nausea makes food unappealing, wearing loose, comfortable clothing as bloating develops, and pacing physical activity down slightly rather than maintaining an intense exercise routine, are all commonly recommended. None of these prevent side effects outright, but they tend to make the ordinary, expected ones easier to sit with, and give you a sense of active participation in your own comfort during a fortnight that can otherwise feel like something that is simply happening to you. Many clinics also provide a written symptom guide at the start of stimulation, worth keeping somewhere easy to find, so you are never relying purely on memory to judge whether something you are feeling falls inside or outside the ordinary range on any given day.
This article summarises commonly reported side effects and is not medical advice or a substitute for your clinic's guidance. Always follow the specific red-flag instructions your own clinic gives you, and contact them directly with any concerns during your cycle.
References
- Cofertility (2026) Side effects and risks of egg freezing. Available at: https://www.cofertility.com/freeze-learn/side-effects-and-risks-of-egg-freezing (Accessed: 23 September 2026).
- CUH NHS Foundation Trust (2026) Egg freezing: information for patients. Available at: https://www.cuh.nhs.uk/patient-information/egg-freezing-information-for-patients/ (Accessed: 23 September 2026).