The aim of this study is to determine whether direct tubal flushing with oil-based contrast at HSG incorporated in the fertility work-up results in 10% more ongoing pregnancies and a shorter time to pregnancy, which will therefore be effective and cost-effective compared to delayed tubal flushing 6 months after fertility work-up is completed in women at low risk for tubal pathology.

Rationale: The investigators hypothesize that direct tubal flushing with oil-based contrast at HSG incorporated in the fertility work-up results in 10% more ongoing pregnancies and a shorter time to pregnancy compared to delayed tubal flushing 6 months after fertility work-up is completed in women at low risk for tubal pathology, which will lead to a reduction in the need for expensive fertility treatments like IVF and/or ICSI, and will therefore be an effective and cost effective strategy.

Objective: The aim of this study is to determine whether direct tubal flushing with oil-based contrast at HSG incorporated in the fertility work-up results in 10% more ongoing pregnancies and a shorter time to pregnancy, which will therefore be effective and cost-effective compared to delayed tubal flushing 6 months after fertility work-up is completed in women at low risk for tubal pathology.

Study design: The investigators plan a multicentre randomized controlled trial with an economic analysis alongside it. Infertile women at low risk for tubal pathology will be randomized to direct tubal flushing with oil-based contrast incorporated in the fertility work-up or delayed tubal flushing 6 months after fertility work-up is completed.

Study population: Infertile women 18-38 years of age, who have a spontaneous menstrual cycle and at low risk for tubal pathology, undergoing fertility work-up.

Intervention (if applicable): Direct tubal flushing with oil-based contrast at HSG as part of the fertility work-up compared to delayed tubal flushing 6 months after the fertility work-up is completed.

Main study parameters/endpoints: The primary outcome is time to live birth, calculated from positive pregnancy test and within 12 months after randomization.

Our hypothesis is that tubal flushing at HSG with oil-based contrast incorporated in the fertility work-up will result in 10% more ongoing pregnancies and a shorter time to pregnancy, and thus reducing the need for ART and reducing costs.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness: As two strategies are compared (tubal flushing with oil-based contrast at HSG incorporated in the fertility work-up versus 6 months after completion of fertility work-up) that are already applied in current practice, no additional risks or burdens are expected from the study.

Inclusion Criteria:

• Women between 18-39 years of age
• Spontaneous menstrual cycle
• Perceived low risk for tubal pathology
• Undergoing fertility work-up

Exclusion Criteria:

• Women with known endocrine disorders (e.g. the polycystic ovary syndrome, diabetes, hyperthyroidism and hyperprolactinemia. Except for well managed hypothyroidism with TSH between 0.3 and 2.5mIU/l)
• Ovulation disorders defined as less than eight menstrual cycles per year
• Iodine allergy
• Male subfertility defined as a post-wash total motile sperm count < 1 x10^6 spermatozoa/ml
• Not willing or able to sign the consent form