Public Release: 

Study suggests tightening up of criteria for definition of intrauterine growth restriction

Society for Maternal-Fetal Medicine

In a study to be presented on February 14 between 1:15 p.m., and 3:30 p.m. PST, at the Society for Maternal-Fetal Medicine's annual meeting, The Pregnancy Meeting ™, in San Francisco, researchers will report that the practice of using an arbitrary Estimated Fetal Weight (EFW) less than the 10th centile may not be an efficient practice for defining true Intrauterine Growth Restriction (IUGR).

The study was conducted by the Perinatal Ireland Research Consortium, a nationwide collaborative research network comprising of the seven largest academic obstetric centers in Ireland. The PORTO Study, which was funded by the Health Research Board (HRB) in Ireland, investigated the optimal management of the IUGR fetus.

Between January 2010 and June 2012, the PORTO Study recruited 1,200 pregnancies with babies who were affected by intrauterine growth restriction, defined as having an EFW on ultrasound below the 10th centile for gestation. The study aimed to challenge whether this traditional definition on its own really matters in predicting poor pregnancy outcome. All eligible pregnancies underwent serial ultrasound evaluation at 2-week intervals until birth. Outcomes for mothers and their babies were recorded.

"Our study demonstrates that almost all of the adverse outcomes associated with having a growth restricted fetus occur in the group of pregnancies with EFW less than the 3rd centile, or when additional abnormal ultrasound features are found," said Dr. Julia Unterscheider of the Royal College of Surgeons in Ireland.

Dr. Sean Daly, a senior co-author of the study further suggested, "For example, having an EFW less than the 10th centile, but greater than the 3rd centile, together with otherwise normal ultrasound features, was almost always associated with delivery of a normal healthy baby."

Of 1,200 recruited pregnancies with EFW below the 10th centile, 78 percent were enrolled before 34 weeks' gestation and detailed outcomes were obtained on 98 percent of all patients. Overall, there were four stillbirths and four neonatal deaths corresponding to an overall perinatal mortality rate of 7.2 per 1,000 births, but all of these deaths occurred in the sub-group of pregnancies with EFW less than the 3rd centile. There were very few adverse outcomes found in the group with EFW between the 3rd and 10th centiles and in whom other ultrasound features were normal.

This study suggests more precise criteria for the diagnosis of true IUGR based on pregnancy outcomes and challenges the reader to re-think the traditional cut-offs used for the definition of intrauterine growth restriction. Professor Fergal Malone, Chairman of the Perinatal Ireland Research Consortium commented, "The major benefit of this study is the potential to radically change the focus and intensity of current methods of fetal surveillance for the apparently small fetus diagnosed prenatally."


A copy of the abstract is available at and below. For interviews please contact Vicki Bendure at 202-374-9259 (cell), or Meghan Blackburn at, 540-687-5099 (office) or 859-492-6303 (cell).

The Society for Maternal-Fetal Medicine (est. 1977) is a non-profit membership group for obstetricians/gynecologists who have additional formal education and training in maternal-fetal medicine. The society is devoted to reducing high-risk pregnancy complications by providing continuing education to its 2,000 members on the latest pregnancy assessment and treatment methods. It also serves as an advocate for improving public policy, and expanding research funding and opportunities for maternal-fetal medicine. The group hosts an annual scientific meeting in which new ideas and research in the area of maternal-fetal medicine are unveiled and discussed. For more information, visit or

Abstract 25:

Julia Unterscheider1, Sean Daly2, Michael Geary3, Mairead Kennelly4, Fionnuala McAuliffe5, Keelin O'Donoghue6, Alyson Hunter7, John Morrison8, Gerard Burke9, Patrick Dicker10, Elizabeth Tully1, Fergal Malone1

1Royal College of Surgeons in Ireland, Obstetrics & Gynecology, Dublin, Ireland; 2Coombe Women and Infants University Hospital, Obstetrics & Gynecology, Dublin, Ireland; 3Rotunda Hospital, Obstetrics & Gynecology, Dublin, Ireland; 4Coombe Women and Infants University Hospital, UCD Center for Human Reproduction, Dublin, Ireland; 5National Maternity Hospital, UCD Obstetrics & Gynecology, School of Medicine and Medical Science, Dublin, Ireland; 6University College Cork, Cork University Maternity Hospital, Obstetrics & Gynecology, Cork, Ireland; 7Royal Jubilee Maternity Hospital, Obstetrics & Gynecology, Belfast, Ireland; 8National University of Ireland, Obstetrics & Gynecology, Galway, Ireland; 9Mid- Western Regional Maternity Hospital, Obstetrics & Gynecology, Limerick, Ireland; 10Royal College of Surgeons in Ireland, Epidemiology & Public Health, Dublin, Ireland.

OBJECTIVE: The PORTO Trial is a multicenter prospective trial conducted at the seven largest obstetric centers in Ireland, with its goal being to evaluate optimal management of the IUGR fetus. For the purposes of the Trial, IUGR was defined as EFW less than the 10th centile. It is unclear however whether this definition is of clinical significance. The objective of this analysis is to document the outcomes of this population.

STUDY DESIGN: A total of 1,056 ultrasound-dated singleton pregnancies with EFW <10th centile were recruited between 24 0/7 and 36 6/7 weeks 'gestation between January 2010 and June 2012. Perinatal and early neonatal outcomes were documented for all participants.

RESULTS: Of 1,056 pregnancies with EFW <10th centile at recruitment, 820 (78%) remained <10th centile until delivery. 492 (47%) had abnormal umbilical artery (UA) Doppler's and 82 (8%) developed UA AEDF or REDF. Table 1 summarizes the maternal and fetal characteristics. Mean gestational age (GA) at enrollment and delivery were 29.8 and 37.6 weeks, respectively. There were 8 aneuploidies and 40 congenital anomalies. The overall perinatal mortality rate in this cohort was 14.2 per 1000 births. Among the normally formed infants with normal karyotype, there were 6 stillbirths (1:170) and 5 neonatal deaths (1:200).

CONCLUSION: Having an EFW less than the 10th centile is a transient finding in 22% of pregnancies. For the remaining 78% with persistently low EFW, constitutionally small size, rather than pathologic IUGR, is by far the most likely outcome. This calls into question the utility of EFW less than the 10th centile as a definition for possible IUGR. A careful evaluation of possible underlying structural or karyotypical abnormalities is warranted in these pregnancies.

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