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CoSy-trial (ZinenZwangerstudie)


Internet-based sex COunselingand chances on natural conception in couples with idiopathic SubfertilitY: arandomized clinical trial

Go to the CoSy website.


About 20,000 Dutch couplesper year are faced with subfertility as they fail to conceive after at leastone year of unprotected intercourse. 5,000 Of these heterosexual couples are diagnosedwith unexplained subfertility and a good prognosis (≥ 30% chance on a live-bornchild after natural conception within 12 months). The guidelines of the DutchSociety of Obstetrics and Gynaecology (NVOG) and the Dutch College of Generalpractitioners (NHG) currently advise postponing medically assisted reproduction(MAR) for six months in these couples as this is equally effective as sixmonths of intra-uterine insemination (IUI) with controlled ovarian stimulation.Until now, expectant management simply means sending couples home forcontinuing to attempt natural conception without guidance on sexual activity,surveillance or support.

Expectant management proves to be challenging in clinical practice because of pressure fromdesperate couples who have a lack of confidence in natural conception and whooverestimate success rates of MAR.

According to a small cohort study, sex counselling canincrease the proportion of couples having intercourse during their fertile daysand can thereby increase ongoing pregnancy rates. Whether sex counsellingindeed increases ongoing pregnancy rates, however, has never been demonstratedin a randomized clinical trial.


To compare the effectiveness, expressed in termsof naturally conceived ongoing pregnancy rate, and the cost-effectiveness ofsix months of internet-based sex counseling to six months of expectantmanagement without guidance on sexual activity, surveillance or support incouples with unexplained subfertility and a good prognosis.

Study design
An international (the Netherlands and Belgium)multicentre Randomized Clinical Trial (RCT) with cost-effectiveness analysis.

Study population
Heterosexual couples diagnosed in Dutch or Belgiansecondary or tertiary fertility clinics with unexplained subfertility and agood prognosis, in which the woman is at least 18 years old. Couples arediagnosed with unexplained subfertility and their calculated prognosis on anongoing pregnancy after natural conception is at least 30% within 12 months. Inaddition, being eligible for this trial requires that no somatic orpsychological problems interfering with the couplesí ability to haveintercourse have been identified during history taking and basic fertilityworkup.

Intervention [or: Methods]
Six months of internet-based sex counselling in 8consecutive modules (experimental arm) versus expectant management withoutadditional counselling for six months (standard or control arm).


Outcome measures
The primary outcome is ongoing pregnancy (i.e. aviable intrauterine pregnancy of at least 12 weeks duration confirmed on anultrasound scan) naturally conceived within six months after randomization.

The secondary outcomes are: time to pregnancy, meanchange in sexual activity, mean change in each partnersí sexual functioning,mean change in individual wellbeing of each partner, health care expenditure.


Power/data analysis
Assuming an ongoing pregnancy rate of 27% in thecontrol group(7) and 35% in the intervention group and 10% drop-out, we willneed 582 couples in each arm (two-sided test, power of 80%, alpha=0.05).

Economic evaluation
The time horizon of the cost andcost-effectiveness analysis will be six months after randomization or until anongoing pregnancy conceived within six months is confirmed by ultrasound.Average costs per couple of the internet-based sex counselling will becalculated from the perspectives of the healthcare system and of the healthcare payer. The costs per ongoing pregnancy in both arms of the RCT (internetbased sex-counseling or expectant management) will be calculated and comparedusing a decision model to take costs, ongoing pregnancies and QALY intoaccount.

A total of 36 months will be needed.

dr. IM Custers


AMC Amsterdam


dr. M. van Wely


AMC Amsterdam 

E: m.vanwely@amc.uva.nl



Contact (researcher)

dr. E.A.F.Dancet


Centre forReproductive Medicine

AcademicMedical Centre, the Netherlands


T: +3120 5667403