Best Time for IUI after hCG Shot Compared (36 vs 42 Hours)

Home » IUI » Best Time for IUI after hCG Shot Compared (36 vs 42 Hours)

Best time for IUI after hCG shot compared (36 vs 42 hours)

Comparing the Effectiveness of Doing Intra-uterine Insemination 36 and 42 Hours After Human Chorionic Gonadotropin (HCG) Injection on Pregnancy Rate: A Randomized Clinical Trial


Several studies have previously investigated the optimal time for IUI following hCG injection however there is still a lack of consensus among the research community due to recent reports.

In 2016 a new study found a significant increase in the pregnancy rate by delaying IUI to 48 hours, after hCG injection, contrary to the findings of a Cochrane systematic review in 2014.

For this reason further studies are now required to confirm if delayed IUI beyond the normal 36 hours is of clinical significance for couples.


A randomized clinical trial of women with unexplained infertility was performed to find any difference in pregnancy rates following intra-uterine insemination, 36 and 42 hours, post human chorionic gonadotropin (hCG) injection.

Women were initially recruited from the educational hospital (Ali Ibn Abi Talib) in Zahedan, Iran. After assessment against the set inclusion / exclusion criteria, a total of 154 women undergoing IUI for the first time participated in the trial.

The women were then randomly divided into 2 groups, with Group 1 (n=77) undergoing IUI 36 hours, post hCG injection, and Group 2 (n=77) 42 hours post injection. For reference, all male partners had normal semen analysis.

Ovarian stimulation was carried out using Letrozole followed by booster shots of HMG (human menopausal gonadotropins) on day 10 as required. Once 1 or 2 follicles reached 18µm or greater, a hCG trigger shot was injected to induce ovulation.

On the day of transfer, semen samples were then prepared according to procedure, using a swim up double wash technique. A fixed volume (0.5cc) of prepared semen was then transferred into the catheter, for injection into the cervix, with progesterone support administered the next day.

Interestingly participants were advised to have sexual intercourse 12 hours after IUI to maximise the rate of fertilisation among women who may not ovulate in a timely manner.

Serum β-hCG levels were measured 16 days after hCG injection to assess for clinical pregnancy with transvaginal ultrasound carried out 4 weeks later to confirm clinical pregnancy. Patients were then followed up till the 12th week of gestation to confirm ongoing pregnancy or other outcomes (ectopic, twins, abortion).


Of the 154 initial women, 150 completed the trial (Group 1 [36hr] = 74, Group 2 [42hr] = 76). Basic characteristics of each group showed no significant differences in mean age, BMI, AMH, TSH, Prolactin or infertility duration.

Analysis of results however showed significant differences between the 2 groups, with higher chemical (32% vs 14%) and clinical (28% vs 14%) pregnancy rates in the post 42 hour IUI group, while rates of abortion or twin pregnancy’s did not differ significantly.

Overall this study adds further weight to the body of evidence suggesting IUI 42 hours post ovulation may result in significantly higher rates of pregnancy per each cycle of IUI.


According to this study and others, the best time for IUI after injecting the hCG trigger shot is 42 hours, causing a doubling in the clinical pregnancy rate (28% vs 14%), which may be explained by the large window of time in which follicle rupture can occur naturally (36 to 48 hours).


  1. Small sample size overall
  2. Live birth rates not reported

Similar studies

Yumusak O H, et al. (2017). Does intrauterine insemination timing matter for achieving pregnancy during ovulation induction using gonadotropins? A retrospective cohort study.

Soliman B S, et al. (2016). Effect of time interval between human chorionic gonadotropin injection and intrauterine insemination on pregnancy rate.

Kamel A M, et al. (2015). The effect of delaying intrauterine insemination till 48 h after hCG injection on pregnancy rate.

Weiss A, et al. (2015). A randomized trial comparing time intervals from HCG trigger to intrauterine insemination for cycles utilizing GnRH antagonists.


Irregular Periods Overview

Ovulation disorders are very common and present in 18-25% of couples who see a specialist for infertility treatment. In the general population…. Read more

Polycystic Ovary Syndrome Overview

Polycystic ovary syndrome is a common endocrine condition that affects how a woman’s ovaries work. Described as a low-grade chronic…. Read more

Questions or comments?