Follicular aspiration as well as follicular flushing are standardized techniques and have been practiced in polyfollicular IVF (in vitro fertilization) therapy for years. Monofollicular IVF therapy is a standard technique as well. IVF can be done in natural cycles or with a minimal stimulation with clomifen citrate to achieve a monofollicular response. Our study aims to compare follicular aspiration and follicular flushing in monofollicular stimulation. First the investigators want to answer the question whether flushing is beneficial for the oocyte yield. In case of a positive result the investigators want to establish a recommendation about the optimal number of flushings taking into account the duration of the procedure and the pain during manipulation.

There is an increase in mono- and oligofollicular IVF therapies worldwide. With the increase in oligo- and monofollicular IVF techniques, a re-evaluation of the aspiration techniques is necessary. The lower the number of mature follicules, the higher the need to obtain the oocyte. The number of embryos obtained is dependent on the number of oocytes retrieved (Wood 2000).

Von Wolff et al. showed (2013) that, three flushings almost doubled not only the number of aspirated oocytes but also the transfer rate in monofollicular IVF. Oocytes, collected by flushing, were as mature and fertilizable as those aspirated without flushing. Mendez Lozano et al. performed an aspiration without flushing in 79 women and with triple flushing in 47 women. They were stimulated with HMG (human menopausal gonadotropin) and controlled with GnRH (Gonadotropin releasing hormone) antagonists in a semi natural cycle IVF. The percentage of patients with a good embryo was 28.8% in the group without flushing and 37.8% in the group with flushing; however, the difference was not significant. Women with an indication for an IVF therapy and the wish of natural cycle IVF are randomized to the intervention (flushing) or control arm (no flushing). In natural cycle IVF, there is no gonadotropin stimulation. Clomifen citrate (25mg e.g. Serophene®, Merck Serono, from the 6th day of cycle) or singles doses of GnRH-antagonists (e.g. Orgalutran®, MSD, Merck Sharp & Dohme AG) are only given to avoid premature ovulation. Once maturity of the follicle is achieved (follicle size ≥16mm), 5000IU urinary human chorionic gonadotropin (uHCG) is used to trigger ovulation. Oocyte pickup (OPU) is performed 36.5 (36-37) hours after ovulation induction. No anesthesia is used for this procedure. For the aspiration 19 gauge single lumen needles are used. After the aspiration the needle is removed and flushed. Depending on randomisation the follicle is not flushed (group A) or flushed adapted to follicule size (16mm 2ml, 18mm 3ml, and 20mm 4ml etc.) up to five times with (e.g.flushing media with heparin (SynVitro® Flush, Origio, Berlin, Germany). In case more than 1 follicle develops, only the largest follicle is analysed. The flushings are collected each in a separate collecting tube (group B). The analysis of the collected oocytes is performed in the IVF lab. The aspirated fluid is analyzed in the IVF lab by the independent biologist. Pain is monitored by VAS (visual analogue scale) score and time of intervention is measured. In the IVF lab the oocytes are fertilised by ICSI (intracytoplasmatic sperm injection) and the embryo transferred 2-3 days later.

Inclusion Criteria:

• Indication for in vitro Fertilisation
• Desire of natural cycle IVF and ICSI fertilisation
• Regular menstrual cycle, both ovaries can be reached for follicule aspiration
• 18-42 years
• size of the follicle ≥16mm
• max. 2 previous embryo transfers

Exclusion Criteria:

• <18 and >42 years
• Preterm ovulation
• >= 3 previous embryo transfers