Nearly 42,000 women got a foetal anomaly ultrasound in 2016
One-in-four Irish maternity units do not offer pregnant women scans for fatal foetal abnormalities.
The ultrasounds are considered a routine part of antenatal care in many other countries, according to researchers at University College Cork (UCC).
A team conducted a telephone survey of all 19 obstetric units in Ireland.
It found every unit has a dedicated Early Pregnancy Assessment Ultrasound service, while 84% of the units have a dedicated maternity ultrasound department.
Foetal anomaly ultrasound is offered to all women in 37% of units, selectively to some women in 37% of units and not offered at all in the remaining 26%.
"In units offering selective anomaly scanning the variation in percentage of women receiving a scan ranges from 10-42%," it adds.
Overall 41,700 women received a foetal anomaly ultrasound nationally in 2016.
The researchers say: "Obstetric ultrasound is a recognised and necessary component of good antenatal care.
"Internationally, the widely accepted minimal schedule for antenatal ultrasound comprises of two examinations.
"Routine first trimester ultrasonography is usually performed between the gestational age of 10+0 and 13+6 weeks.
"This is the most appropriate time point at which to accurately date a pregnancy".
The paper, which is published in the Irish Medical Journal, adds: "The foetal anomaly scan is best performed between 20+0 to 22+6 weeks’ gestation as this time point allows the best visualisation of foetal anatomical structures".
The Royal College of Obstetricians and Gynaecologists (RCOG) has recommended since the year 2000 that all pregnant women should be offered these two ultrasounds.
A two-stage ultrasound is also endorsed by the National Institute for Health and Clinical Excellence (NICE).
In January 2016, the Department of Health published the National Maternity Strategy.
This recommended all women have "equal access to standardised ultrasound services, to accurately date the pregnancy (and) to assess the foetus for ultrasound diagnosable anomalies as part of a planned Prenatal Foetal Diagnostic Service".