When to Time Sex or IUI After Trigger Shot

You took the trigger shot tonight at 9pm, and now you are looking at the next two days trying to work out exactly when to have intercourse, or when your IUI is scheduled, or both. This post breaks down the hours after the shot in concrete terms, so you can stop refreshing forum threads and just follow a plan.

The cleanest fact about trigger shot timing is this: ovulation occurs 36 to 40 hours after the injection in the great majority of cycles.¹ Everything else, when to have sex, when IUI is scheduled, whether to do anything on the night of the shot, all flows from that one number.

Trigger shot timing, hour by hour

If you took the trigger at 9pm on a Tuesday night, the cycle runs like this.

• Hour 0 (Tuesday 9pm): Trigger injection.
• Hour 12 to 24 (Wednesday morning to Wednesday evening): Egg is finishing its final maturation inside the follicle. The follicle wall is starting to thin.
• Hour 24 to 36 (Wednesday evening to Thursday morning): Pre-ovulatory phase. Most IUIs are scheduled here.
• Hour 36 to 40 (Thursday morning to Thursday afternoon): Ovulation. The egg is released into the fallopian tube.
• Hour 40 to 64 (Thursday afternoon through Friday): Egg is viable for fertilisation for roughly 12 to 24 hours after release.²

Sperm, by comparison, survives 3 to 5 days in fertile cervical mucus. The Wilcox NEJM study on timing of intercourse and conception is the foundational evidence on this: the highest-probability days for conception are the day of ovulation and the five days before it, with peak probability in the two days immediately before ovulation.² In a triggered cycle, those two days are the night of the trigger and the day after.

If you are doing IUI

IUI cycles are scheduled around the trigger, not the other way around. Most clinics aim to place the washed sperm in the uterus 24 to 36 hours after the trigger injection, which puts the sperm in the tubes just before the egg is released.³ This is why your trigger time was given as a specific hour, not just a date.

A few practical points.

Arrive on time. The sperm sample is prepared in the lab on a timed schedule. If you are late, the sample may have to be re-prepared, and the timing margin narrows.

Some clinics do back-to-back IUI. Two inseminations in one cycle, usually 12 and 36 hours after trigger. Cochrane reviews have not found a consistent advantage of double IUI over single IUI for most indications,⁴ but some clinics use it for severe male-factor or when timing is uncertain. If your clinic uses single IUI, that is the evidence-based standard.

Intercourse the night of the trigger is generally fine. Many patients also have intercourse on trigger night before the IUI the next morning. This provides backup sperm in case the IUI timing is slightly off. Confirm with your clinic, because some practices ask you to abstain for 48 to 72 hours before the IUI to optimise the sperm sample your partner provides.

Intercourse the night after IUI is fine and may add a small benefit. There is no evidence that intercourse displaces the washed sperm from the uterus.

If you are doing timed intercourse only

If your cycle is letrozole or clomid with a trigger but no IUI, the goal is to cover the fertile window with multiple opportunities. The pattern I usually recommend is:

1. Trigger night: intercourse the same evening as the shot. Sperm needs hours to transit through the cervix and into the fallopian tubes, and having sperm already in position when ovulation occurs is the most reliable strategy.
2. Day after trigger (about 24 hours later): intercourse again. Sperm survival is days, but topping up the supply ensures fresh, motile sperm is in the tubes at the moment of ovulation.
3. Two days after trigger (about 48 hours later): intercourse one more time. The egg may still be viable, and this catches any cycle that ovulates slightly later than expected.

Day 3 after trigger is optional. By then, the egg is past its viable window in most cycles, but for couples who want to add one more opportunity at a low cost, there is no harm.

What about frequency? Most studies on intercourse frequency are reassuring: daily intercourse during the fertile window does not deplete sperm quality in couples with normal semen parameters. If your partner has known low motility or count, your RE may suggest every-other-day intercourse to optimise the sample. Confirm with your clinic.

Why the night of the trigger matters

This is the timing question I get most often. Patients ask whether intercourse on the night of the shot is worthwhile, or whether they should wait for the morning after, since ovulation is not yet happening.

The answer is that the night of the trigger matters, and skipping it loses ground.

Sperm transit through the cervix into the fallopian tubes takes several hours. The sperm population that fertilises the egg has typically been waiting in the tubes for some time. By having intercourse on the night of the trigger, you put sperm into transit so that by the time the egg is released roughly 36 hours later, sperm is in position.

If you skip the trigger night and have intercourse only the day after, the margin narrows. There is still a fertile window, but you are relying on sperm getting from the cervix to the tubes in a tighter window. For couples with no male-factor issues, this still works. For couples where every variable matters, the trigger night is an easy win.

Common timing mistakes

A few patterns I see in clinic that are worth naming.

Treating the OPK like it still matters: after a trigger shot, your urine LH will read positive because the trigger itself produces an LH-like signal. Patients sometimes wait for an OPK to turn positive after the trigger to confirm the timing, which delays the fertile window unnecessarily. Once the trigger is in, the OPK is no longer the navigation tool. The clock is.

Waiting until 48 hours post-trigger and missing the peak: some couples plan intercourse only for 48 hours post-trigger, on the theory that ovulation will have just happened. The window is still open at 48 hours, but the egg is past its peak viability and may have already been fertilised or not. Earlier is better.

Trying to ovulate "naturally" after the trigger: the trigger overrides any natural surge. Whatever pattern you have noticed in past unmedicated cycles, set it aside for this one. The shot sets the clock.

Worrying that bloating means OHSS: mild bloating starting 12 to 24 hours after the shot is the expected response of the dominant follicle to hCG. OHSS is uncommon in oral medication cycles. The pattern that worries me is rapid abdominal distension, severe pain, or reduced urine output, not the mild fullness most patients feel. I have a longer post on Ovidrel side effects that covers what to watch for.

What if you ovulated early or late

Most patients ovulate in the 36 to 40 hour window. A smaller proportion ovulate slightly outside it.

Earlier ovulation (less than 24 hours post-trigger) is uncommon when follicle sizing is correct.⁵ The follicle has to be mature enough to respond to the LH signal, and clinics trigger at sizes (typically 18 to 22mm) that produce a reproducible 36 to 40 hour window. If you have a history of early ovulation despite an appropriately sized follicle, your RE may take that into account on the next cycle.

Later ovulation (more than 40 hours post-trigger) happens occasionally and is more common with slightly smaller follicles or higher individual variability. If your follow-up scan or beta hCG suggests timing was off, this is data for the next cycle. One cycle is not a verdict.

A useful framing: timing is rarely the single reason a cycle does not work. Sperm survival, egg quality, tubal patency, and implantation all matter. If a cycle does not result in pregnancy, "the timing must have been wrong" is rarely the right conclusion.

A simple plan to follow tonight

If you took the trigger tonight and want a one-paragraph plan to execute, here it is.

Set an alarm for trigger night intercourse if needed. Plan intercourse again the following evening, and again the evening after that. If your IUI is the morning after the trigger, confirm whether your clinic wants abstinence first, and assume intercourse is fine the night after the IUI. Watch for the side effects in the Ovidrel post, but expect mild bloating and a quieter cycle than the build-up suggests. Two weeks from the trigger, you have a beta hCG draw. Do not test at home before then unless you understand that any positive in the first week is the shot, not pregnancy.

What's next

• If you want the foundational explainer: The HCG Trigger Shot: What It Does and Why You Take It
• If you are doing IUI tomorrow and want to know what happens: IUI Explained
• If you tested early and saw a faint line: Trigger Shot False Positives on Pregnancy Tests
• If your cycle is unmedicated next time: Timing Intercourse: When and How Often

Sources

1. Andersen AG, Als-Nielsen B, Hornnes PJ, Franch Andersen L. Time interval from human chorionic gonadotrophin (HCG) injection to follicular rupture. Human Reproduction 1995;10(12):3202-3205. https://doi.org/10.1093/oxfordjournals.humrep.a135888
2. Wilcox AJ, Weinberg CR, Baird DD. Timing of sexual intercourse in relation to ovulation. Effects on the probability of conception, survival of the pregnancy, and sex of the baby. New England Journal of Medicine 1995;333(23):1517-1521. https://www.nejm.org/doi/full/10.1056/NEJM199512073332301
3. Practice Committee of the American Society for Reproductive Medicine. Evidence-based treatments for couples with unexplained infertility: a guideline. Fertility and Sterility 2020;113(2):305-322. https://doi.org/10.1016/j.fertnstert.2019.10.014
4. Cantineau AEP, Janssen MJ, Cohlen BJ, Allersma T. Synchronised approach for intrauterine insemination in subfertile couples. Cochrane Database of Systematic Reviews 2014;(12):CD006942. https://doi.org/10.1002/14651858.CD006942.pub3
5. Goldman MB, Thornton KL, Ryley D, et al. A randomized clinical trial to determine optimal infertility treatment in older couples: the Forty and Over Treatment Trial (FORT-T). Fertility and Sterility 2014;101(6):1574-1581. https://doi.org/10.1016/j.fertnstert.2014.03.012
6. Damewood MD, Shen W, Zacur HA, Schlaff WD, Rock JA, Wallach EE. Disappearance of exogenously administered human chorionic gonadotropin. Fertility and Sterility 1989;52(3):398-400. https://pubmed.ncbi.nlm.nih.gov/2670598/