IRIS study

Of all babies that die after 25 or more weeks of gestation, 40% are small-for-gestational age (SGA). In the Netherlands third trimester ultrasound (US) screening is increasingly being used to monitor fetal growth, even though evidence on its effectiveness and cost-effectiveness is lacking.

The IRIS study fills the urgent need to evaluate the value of third trimester US in monitoring fetal growth among low risk women in primary care. If shown to be effective, routine third trimester US will contribute to reducing the national perinatal mortality and severe morbidity rate. 


Data collection of the IRIS study has started on January 1st, 2015.

Study design
A nationwide stepped wedge cluster randomised trial in which primary care midwifery practices will be randomised.

Women who receive/continue care in the participating midwifery practice after the 20 weeks structural ultrasound and who have a singleton pregnancy.

Primary outcomes
The clinical primary outcome is a dichotomous composite measure 'severe adverse perinatal outcome' up to 7 days after birth, including: perinatal death; Apgar score below 4 at 5 minutes after birth; impaired consciousness; need for assisted ventilation for more than 24 hours; asphyxia; septicaemia; meningitis; bronchopulmonary dysplasia; intraventricular haemorrhage; cystic periventricular leukomalacia; neonatal seizures or necrotizing enterocolitis. Also direct and indirect costs are primary outcomes.

Sample size
A total of 15.000 women in 60 midwifery practices.

Main data analysis and economic evaluation
Multivariable logistic regression analyses, taking into account the clustered design. The economic evaluation will consist of a cost-effectiveness and a cost-utility analysis and will be performed from both a health care provider and societal perspective. We will base all primary analyses on intention to treat.

Pre-planned sub-studies
We will perform two sub-studies. In sub-study A we will develop the IRIS consensus-based protocol for detection and management of suspected SGA, including the role of third trimester US, and study professionals' adherence to this protocol. In sub-study B we will evaluate women's positive and negative experiences with the approach to fetal growth monitoring in the third trimester, including informed choice and dealing with unclear, incorrect and unexpected US findings. If more funding will become available, other sub-studies will be carried out as well.

48 months.

Study Protocol (23-10-2014)

Leaflet IRIS study (27-10-2014)

Baseline data IRIS study

Informed Consent IRIS study (27-10-2014)