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What is selective intrauterine growth restriction (sIUGR)?

Selective intrauterine growth restriction is present  when the fetal weight of one twin is  below the 10th percentile [1]  in one twin of a monochorionic  twin pregnancy while the co-twin is of normal size . sIUGR affects 12 - 25 % of monochorionic
(one placenta) twin pregnancies and is thought to be caused by unequal sharing of the placenta by the twins [2] .

In growth restricted fetuses ultrasound  Doppler velocimetry is used  to evaluate the hemodynamic status of the fetus.  Pulsed Doppler is performed on the umbilical arteries (UAs) in a free loop of umbilical cord, with the angle of insonation as near to zero as possible, in the absence of fetal and maternal breathing .  The figures below show three main patterns of blood flow that can be detected.

Positive end-diastolic flow in the umbilical artery (normal) Absent end-diastolic flow in the umbilical artery  Reversed end-diastolic flow in the umbilical artery

S = Systolic flow ;Flow through the umbilical artery during contraction of the fetal heart. D = End-diastolic flow; Continuing forward flow in the umbilical artery during the relaxation phase of the heartbeat

Gratacós E, et. .al have suggested fetuses with sIUGR may be classified into three types based on one of three main umbilical artery Doppler waveform patterns, as defined by the characteristics of diastolic flow: positive, persistently absent/reversed or intermittently absent/reversed .
Classification of sIUGR  [2]:

  • Type I (positive end-diastolic flow in the umbilical artery)
  • Type II (AREDF) : persistently absent or reversed end-diastolic flow
  • Type III (iAREDF). intermittent absent or reversed end-diastolic flow in the absence of fetal breathing.

Using the above classification system Gratacós E et. al. followed 134 MC twins diagnosed with sIUGR.  Fetal well-being was monitored by serial evaluation of Doppler waveforms in the umbilical arteries , middle cerebral artery and ductus venosus, in combination with fetal biophysical profile, and, from 28 weeks’ gestation onwards, fetal heart rate patterns[2].

Hospital admission was contemplated beyond 28 weeks if there was persistent AREDF in the UA Doppler examination, brain-sparing effect or abnormal ductus venosus Doppler flow. The management protocol considered the option of fetoscopy-guided cord occlusion in the smaller twin if severe fetal deterioration was observed before 28 weeks.

Fetal deterioration indicating the need for active management was defined as the presence of :

Before 28 weeks: 

  • Absent or reversed atrial flow in the ductus venosus (DV) *

After 28 weeks:

     Any of the following:

  • Persistent reversed end-diastolic flow in the umbilical artery
  • Ductus venosus pulsatility index (PI) persistently above two SD for gestational age
  • AND/OR persistently abnormal fetal heart rate traces and
    biophysical profile.

The table below shows the prevalence of some selected adverse events found by Gratacós E and co-workers according to the type of sIUGR

Type of sIUGR Prevalence of selected adverse events [2]
Unexpected fetal death Parenchymal brain lesion larger twin Parenchymal brain lesion in smaller twin
I 2.6 % 0 % 0 %
II 0 % 3.3 % 14.3 %
III 15.4 % 19.7 % 2 %
* The duration of absent or reversed flow during atrial systole in the DV has been found to be a strong predictor of stillbirth [5,6 ]

In the Fetus with IUGR The Society for Maternal-Fetal Medicine recommends [3]:

"When Doppler abnormalities are detected in the fetal arterial circulation, weekly follow-up Doppler studies are considered usually sufficient if forward umbilical artery end-diastolic flow persists. In the absence of specific data regarding the optimal frequency of testing, experts have recommended Doppler surveillance up to 2-3 times per week when IUGR is complicated by oligohydramnios, or absent or reversed umbilical artery end-diastolic flow."

  • Twice weekly nonstress testing with weekly amniotic fluid evaluation, or weekly biophysical profile testing, is commonly recommended when IUGR is suspected
  • Antenatal corticosteroids should be administered if absent or reversed end-diastolic flow is noted <34 weeks in a pregnancy with suspected IUGR.
  • Delivery of monochorionic diamniotic twins with isolated fetal growth restriction at 32 0/7–34 6/7 weeks of gestation is recommended [4].


Presently there is no treatment for sIUGR . At early gestational ages cord occlusion (radiofrequency ablation needle) or fetoscopic placental laser coagulation has been offered when the risk of death in the sIUGR twin is very high or imminent in order to prevent brain and other organ damage to the surviving co-twin.



1. Hadlock FP, et al., In utero analysis of fetal growth: a sonographic weight standard. Radiology. 1991 Oct;181(1):129-33.PMID: 1887021
2. Gratacós E, et. .al. A classification system for selective intrauterine growth restriction in monochorionic pregnancies according to umbilical artery Doppler flow in the smaller twin.
Ultrasound Obstet Gynecol. 2007 Jul;30(1):28-34. PMID: 17542039
3. Society for Maternal-Fetal Medicine Publications Committee, Berkley E, Chauhan SP, Abuhamad A.Doppler assessment of the fetus with intrauterine growth restriction.Am J Obstet Gynecol. 2012 Apr;206(4):300-8. doi: 10.1016/j.ajog.2012.01.022. Erratum in: Am J Obstet Gynecol. 2012 Jun;206(6):508. Am J Obstet Gynecol. 2015 Feb;212(2):246. PMID: PMID: 22464066
4. Medically indicated late-preterm and early-term deliveries. Committee Opinion No. 560. American College of Obstetricians and Gynecologists. Obstet Gynecol 2013;121:908–10. PMID:23635709
5. Turan OM, et. al., Duration of persistent abnormal ductus venosus flow and its impact on perinatal outcome in fetal growth restriction.Ultrasound Obstet Gynecol. 2011 Sep;38(3):295-302. doi: 10.1002/uog.9011.PMID:21465604
6.  Morris RK, et. al., Systematic review and meta-analysis of the test accuracy of ductus venosus Doppler to predict compromise of fetal/neonatal wellbeing in high risk pregnancies with placental insufficiency.
Eur J Obstet Gynecol Reprod Biol. 2010 Sep;152(1):3-12. doi: 10.1016/j.ejogrb.2010.04.017. Epub 2010 May 20. PMID:20493624




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