The aim of this study is to establish clinically meaningful ultrasound-based diagnostic criteria for AP. To this end, the investigators will prospectively collect clinical and ultrasound data from early intrauterine pregnancies and correlate this data with pregnancy outcomes (particularly with risk of miscarriage), to establish whether there are any diagnostic criteria that can be used to make the diagnosis, facilitate increased surveillance of at risk pregnancies and reassure those with normally located pregnancies. The collected data will be used to correlate incidence of angular pregnancy and clinical variables such as maternal age, uterine fibroids, assisted conception, multiple pregnancy, ethnicity, previous uterine and adnexal surgery.

Inclusion Criteria:

• Have capacity to understand the study and to provide signed and dated informed consent.
• Willing to comply with all study procedures and be available for the duration of the study including consenting to follow up of the pregnancy outcome by letter, phone or email according to individual preference.
• Age 16 years or over
• Mean gestational sac diameter (GSD) on ultrasound of 2-15mm inclusive
• GS implantation site within the upper half of the uterine cavity on 2D USS

Exclusion Criteria:

• Women with pregnancies of unknown location, ectopic pregnancies or larger GSD than specified in the inclusion criteria.
• Implantation site within the lower half of the endometrial cavity on 2D USS screening.
• Intention to terminate the pregnancy
• Women with unicornuate uteri or unicornuate uteri with rudimentary horns
• Women with uterine fibroids which distort the uterine cavity

Pregnant women who are attending for a scan in the early pregnancy unit, aged over 16 years.

Data is available for reasonable requests including study protocol and anonymised data.