133 cases with cs niche undergoing ART will be included. Pituitary suppression will be achieved by long or antagonist protocol. For long protocol, GnRH agonist will be administered for 10-14 days starting from mid-luteal phase of preceding cycle. After confirmation of down regulation, gonadotropins will be given from second or third day of cycle in a daily dose of (150-300 IU). Gonadotropins therapy will be tailored according to age, BMI, antral follicle count, antimullerian hormone and previous response. In antagonist protocol, gonadotropins will be given from second or third day of cycle in a daily dose of (150-300 IU). GnRH antagonist will be adjusted according to patient response. On the 5th -6th day of stimulation, sonography will be performed and repeated every 1-3 days with regular estradiol assessment. When at least 3 follicles reach ≥ 17 mm in mean diameter, trigger will be given. Oocytes pick up will be performed 34-36 hour after triggering.

133 cases without cs niche undergoing ART will be included. Pituitary suppression will be achieved by long or antagonist protocol. For long protocol, GnRH agonist will be administered for 10-14 days starting from mid-luteal phase of preceding cycle. After confirmation of down regulation, gonadotropins will be given from second or third day of cycle in a daily dose of (150-300 IU). Gonadotropins therapy will be tailored according to age, BMI, antral follicle count, antimullerian hormone and previous response. In antagonist protocol, gonadotropins will be given from second or third day of cycle in a daily dose of (150-300 IU). GnRH antagonist will be adjusted according to patient response. On the 5th -6th day of stimulation, sonography will be performed and repeated every 1-3 days with regular estradiol assessment. When at least 3 follicles reach ≥ 17 mm in mean diameter, trigger will be given. Oocytes pick up will be performed 34-36 hour after triggering.

A niche is formally defined by the European Niche Taskforce as an indentation of the uterine myometrium of at least 2 mm at the site of the CS scars. A niche can be sub classified as follows:

1. Simple niche
2. Simple niche with one branch
3. Complex niche (with more than one branch).

The following measurements will be taken:

• Length.
• Depth.
• Width.
• RMT (residual myometrium thickness).
• AMT (adjacent myometrium thickness).
• Distance between the niche and the VV (vesico-vaginal) fold.
• Distance between the niche and the external os. We will also comment on the position of the uterus (AVF or RVF), presence or absence of intra cavitary fluid and its thickness.

Ongoing pregnancy: defined as a viable intrauterine pregnancy of at least 12 weeks duration confirmed on an ultrasound scan

Clinical pregnancy: A pregnancy diagnosed by ultrasonographic visualization of one or more gestational sacs.