Pregnyl is an hCG injection that starts your ovulation, usually about 36 to 48 hours after it is given. You get it at the end of a stimulation cycle, at the moment your follicles are large enough.
It is one of the oldest drugs in fertility care, and that raises the same question in many women: is this not outdated compared with the modern pens? The honest answer is no, and the studies on it are surprisingly clear.
What is Pregnyl and how does it work?
Pregnyl contains human chorionic gonadotrophin, purified from urine. That hormone closely resembles your own LH, the hormone that normally drives your ovulation. The injection takes over that role temporarily.
Your eggs receive their final maturation signal from it. Without that signal they stay inside the follicle, even when it is large enough.
So Pregnyl does not grow your follicles. The FSH injections in the days before did that, and Pregnyl adds the closing note.
Why do you get Pregnyl in IVF?
Because the retrieval has to be planned to the minute. The clinic wants to collect your eggs when they are just mature but not yet released, and that window is narrow.
By giving the starting signal themselves, the team knows exactly when that window opens. The retrieval is therefore usually planned about 34 to 38 hours after your injection.
That explains why you get such a specific time, often to the quarter hour. If that time does not work out, call your clinic rather than shifting it yourself. More about that day at the IVF egg retrieval.
How many hours after Pregnyl is ovulation?
In most women ovulation follows about 36 to 48 hours after the injection. With an IUI or a natural attempt, many clinics therefore advise intercourse on the evening of the injection and the two days after.
With an IVF retrieval, do not do the maths yourself. The clinic deliberately plans just inside that window, so the eggs are still in the follicle.
Always follow your own treatment team schedule, because protocols differ per clinic and per treatment.
Pregnyl or Ovitrelle: which is better?
On the outcomes that matter they probably do not differ. A Cochrane review of 18 trials with 2,952 participants found no difference between urinary hCG and recombinant hCG in live births, ongoing pregnancies or hyperstimulation (PMID 27106604).
The difference is in convenience, not in the odds.
| Pregnyl | Ovitrelle | |
|---|---|---|
| Active substance | Human chorionic gonadotrophin | Choriogonadotropin alfa |
| Origin | Purified from urine | Recombinant, from cell lines |
| Preparation | Dissolve powder with solvent | Ready to use |
| Administration | Under the skin or into muscle | Under the skin |
| Ovulation after injection | About 36 to 48 hours | About 36 to 48 hours |
| Difference in live births | No difference shown (PMID 27106604) |
So if your clinic prescribes Pregnyl, that is not a second choice. Often it is simply what is in stock or what fits the protocol. Read also Ovitrelle and ovulation timing.
Side effects of Pregnyl
The side effects reported most are pain or redness at the injection site, headache, tiredness, abdominal pain and tender breasts. Because it is usually a single injection, the complaints stay short.
The Farmacotherapeutisch Kompas also lists bloating and, less often, ovarian hyperstimulation syndrome. That last one needs attention, because hCG keeps stimulating your ovaries for days.
Contact your clinic if your belly swells quickly, or with severe abdominal pain, nausea with vomiting, shortness of breath or clearly reduced urine output. Do not wait for the next appointment with that.
A Cochrane review on prevention showed that in women at raised risk the chance of moderate or severe hyperstimulation fell from roughly 27 percent to about 8 to 14 percent with dopamine agonists (PMID 33851429). Those figures apply to the high risk group, not to everyone.
Pregnyl experiences: what do users report?
Preparing it is what women mention most. Dissolving a powder feels awkward if you have never prepared an injection before.
What comes back positively:
- After one demonstration, dissolving it goes fine
- The injection itself is short and usually manageable
- Many women barely notice side effects
- It is a clear turning point in the process
What they find difficult:
- The tension around the exact time
- A heavy or pressing feeling low in the belly afterwards
- With an intramuscular injection, a sore spot that lingers a day
- The temptation to test too early
Picture two women who inject at 9.30 pm on a Tuesday. One feels clear cramps on Thursday morning around the retrieval. The other notices nothing at all and doubts whether it worked. Both have mature eggs at retrieval. Feeling something is not a measure.
Why you should not test too early after Pregnyl
A pregnancy test measures hCG, and Pregnyl is hCG. If you test within about ten days of the injection, you may be measuring the remains of the trigger instead of a pregnancy.
That is why your clinic names a test date rather than leaving you to judge it. A false positive result is emotionally expensive.
A blood test that reports hCG as a number does help here, because you see a rise or a fall instead of a line. See how fast hCG should rise, use the hCG calculator to compare two results, or have the IVF blood test done with an assessment by a BIG-registered doctor. The whole route is laid out at what IVF involves.
Frequently asked questions
How quickly does Pregnyl work?
The hormone starts working immediately, but ovulation follows only about 36 to 48 hours later. You usually notice little in between. Sometimes you feel some pulling pain towards the end of that window.
How many units of hCG are in Pregnyl?
Pregnyl comes in different strengths, and which you get depends on your treatment. A trigger often uses a higher strength than other uses. Check your own leaflet and your clinic schedule.
Where do you inject Pregnyl?
Depending on the prescription, under the skin of your abdomen or thigh, or into a muscle. An intramuscular injection more often aches afterwards. Follow the instruction you were given at the clinic.
How many days after Pregnyl does your period come?
If no pregnancy develops, your period usually comes about two weeks after ovulation. With IVF that differs, because you often also use progesterone. Your clinic will say when you may stop.
Can Pregnyl cause twins?
The injection itself does not raise that chance. The number of mature follicles or embryos transferred does. That is why the clinic counts exactly how many follicles take part before triggering.
My advice would be to have the preparation demonstrated once, calmly, at the clinic, and then not to improvise with the timing at home. The rest of this drug is less dramatic than it feels: a well studied hormone that does one thing, at one moment. Put your clinic test date in your diary and leave the test strips in the cupboard until then.
Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP or your gynaecologist.
References
- Farmacotherapeutisch Kompas. Chorionic gonadotrophin. Accessed 2026.
- Thuisarts.nl. I am having IVF. Accessed 2026.
- Youssef MA, Abou-Setta AM, Lam WS. Recombinant versus urinary human chorionic gonadotrophin for final oocyte maturation triggering in IVF and ICSI cycles. Cochrane Database of Systematic Reviews, 2016. PMID 27106604.
- van Wely M, Kwan I, Burt AL, Thomas J, Vail A, Van der Veen F, Al-Inany HG. Recombinant versus urinary gonadotrophin for ovarian stimulation in assisted reproductive technology cycles. Cochrane Database of Systematic Reviews, 2011. PMID 21328276.
- Tang H, Mourad SM, Wang A, Zhai SD, Hart RJ. Dopamine agonists for preventing ovarian hyperstimulation syndrome. Cochrane Database of Systematic Reviews, 2021. PMID 33851429.
Autor
Lunarahealth
Dr. Naimi, lekarz wpisany do holenderskiego rejestru BIG, nadzoruje standardy medyczne naszych treści i ocen. Przeczytaj naszą politykę medyczną
