Ultrasonography will be used to determine the total blood flow to and from the uterus. This is done by measuring the blood vessels coming from and going to the uterus. This wil hopefully prove viable and open the possibility to further research in the clinical relevance of these measurements.

This prospective pilot study takes place between 14- and 16-weeks' gestation (GA14 to 16 weeks). This is a feasibility study, as the perfusion measurements have not yet been performed this early in pregnancy. First the feasibility is assessed, before conducting a full-scale research project. The study will take place in a tertiary care obstetric centre, Máxima Medical Center, in Veldhoven The Netherlands. Measurements will be done at the out patient clinic of obstetrics. Duration of the study is 2 months. This gives ample time for recruitment of the subjects.

Recruitment will take place at the outpatient clinic of Máxima Medisch Centrum in Veldhoven. Women with singleton pregnancies coming for their 11-12 weeks' gestational ultrasound, where the pregnancy is dated, will be given a patient information folder in either Dutch or English and asked if the researcher can contact them. Participation is completely on voluntary basis. Patients will be called in the next days by the researcher to answer additional questions and to ask if patients are willing to participate. Contact information of the researchers will be available on the folder in case of questions.

Upon inclusion, the patients will be scheduled for a visit to perform all relevant measurements, henceforth referred to as 'measurement day' (MD) which is to take place between 14- and 16-weeks' gestation. The patient, henceforth to be referred to as participant, will be asked to rest for 5 minutes in a supine position. After 5 minutes of rest the blood pressure of the right arm will be measured, three times using the auto-sphygmomanometer. The three measurements will then be used to calculate the average systolic and diastolic blood pressures. After measurement of blood pressure, the ultrasound scan will be performed. The uterine and placental vessels will be measured according to the standard operating procedure attached to this document. All vessels will be measured 3 times during the ultrasound scan.

Inclusion Criteria:

• Age ≥ 18 years
• Between 14-16 weeks gestation on measurement day
• Placenta anterior
• BMI < 30kg/m2
• Ability to give consent
• Adequate mastery of the Dutch or English languages

Exclusion Criteria:

• Non-intact pregnancy at 13 week's gestational echo.
• Vanishing twin
• Multiple gestations
• Congenital or anatomical anomalies at 13 weeks' gestational echo.

The base population are women with singleton pregnancies between 14- and 16 weeks' gestation.