Risks and responsibilities arising from Prenatal Ultrasound
MIDIRS Midwifery Digest 2012:
Cohain JS.
Most people love the occasional scary movie. Adrenalin is released, your heart beat increases and at the end, if it was a really good movie, you have to deliberately calm yourself by reminding yourself that it was just a movie and there is no bogeyman under the bed. The results of routine prenatal ultrasound testing can be equivalent to the impact of a scary movie. You might have to remind yourself afterwards that prenatal ultrasound screening is a cheap thrill that is unable to improve pregnancy outcomes but can have long term physical consequences for the mother, in terms of surgery that could have been avoided, unknown injury to the fetus and all their long term ramifications.
Ten billion years of evolution smoothed out the wrinkles in human birth. In the absence of viable random mutations, smoking, overeating, or drug addiction, every average sized pregnant woman who; eats
Routine Ultrasound screening
Based on systematic meta-analysis of RCT studies failing to show improved outcomes and lack of knowledge of the adverse effects of ultrasound at the doses currently used, the evidence-based recommendation would be to undertake prenatal ultrasound routinely only when ultrasound can be of assistance: see Table 1.
Table 1: Prenatal ultrasound with evidence of improved outcomes
Adjunct to ECV (Turning a breech baby to vertex)
Adjunct to fetal transfusion and amniocentesis
Evaluation of pelvic tumors or fibroids
Evaluation of hydatidiform mole
Evaluation for ectopic pregnancy
Confirmation of fetal death
Confirmation of presentation (where practitioners are not taught how to ascertain evaluate presentation without ultrasound).
The following uses of ultrasound (see Table 2) have been tested in RCT studies on tens of thousands of women. While such tests have the potential to suspect harmful conditions, they have not been shown to improve fetal outcomes. These tests are used to screen for and cleverly diagnose Suspected Fetal Growth Restriction (FGR) as well as Suspected Placental Insufficiency, and/or Suspected Postdates Pregnancy. These diagnoses are routinely used to justify induction of labour or to deliver the baby by cesarean section, supposedly in order to prevent stillbirth. However, the information obtained from these scans have not been shown to be responsible for a decrease in stillbirth rates or lower perinatal mortality rates as was once hoped. Women undergoing induction for a diagnosis of suspected postdates or suspected IUGR have not been shown to have fewer stillbirths in any rigorous research study, nor lower perinatal mortality rates while they do have higher cesarean rates as a result of failed induction (Menticoglou and Hall, 2002). Induction is considered to be an independent risk factor for postpartum haemorrhage (PPH) (Belghiti et al 2011, Sheiner et al 2005).The long term effects of induction on the newborn have also not been elucidated in full.
Table 2: Prenatal ultrasound with no evidence of improved outcomes
- First trimester ultrasounds for dating (Menticoglou and Hall, 2002)
- Second trimester 15 minute Organ Scan: Defects detected with accuracy of 13%-85% & high rates of false positive. (ACOG Practice Bulletin 2009)
- Amniotic Fluid Index (AFI) (Locatelli 2004, Nabhan et al 2008, Magann 2007, Haws et al 2009, Khunpradit et al. 2010)
- Biphysical profile (BPP) (Lalor et al. 2008, Haws et al 2009)
- Placental grading (Moran et al. 2011, Haws et al 2009)
- Doppler velocity for no risk pregnancy (Alfirevic et al. 2010#2, Haws et al 2009)
- Doppler velocity for high risk pregnancy (Alfirevic et al. 2010, Haws et al 2009)
Screening for fetal compromise
Intra-uterine growth retardation, is a term which was recently sanitized or euphemized into Intrauterine growth restriction or fetal growth restriction (FGR), but the meaning is the same. IUGR describes all fetuses estimated to be below the 10th percentile for weight. By arbitrarily defining IUGR as the 10% of fetuses who fall in the bottom 10th percentile, 10% of fetuses will always be defined as having IUGR. The theory proposed to explain why a fetus is in the 10th percentile is because the placenta is limiting the growth of the fetus which, supposedly, will in turn affect their potential growth and development. Under the excuse of attempting to prevent fetal morbidity, once a fetus is judged to be in the 10th percentile, a barrage of prenatal testing is begun. The disconnection between acquiring data and whether benefit arises from taking action based on this data occurs here: As can be seen from table 2, prenatal ultrasound testing for placental insufficiency has not been shown to be useful in improving outcomes. The Organ scan identifies defects that cannot be treated in utero, with large numbers of false positives and negatives. The Amniotic Fluid Index (AFI) fails to predict lack of fetal well-being and had “no prognostic significance”(Locatelli et al 2004) and a Cochrane review found “the use of the amniotic fluid index increases the rate of diagnosis of oligohydramnios and the rate of induction of labor without improvement in peripartum outcomes” (Nabhan and Abdelmoula 2008). Magann (2007) found that single deepest pocket (SDP) measurement is as useless as AFI. When amniotic fluid index (AFI) was done on admission versus no sonographic assessment of AFI on admission, cesarean section for fetal distress was double that of controls, but there was no improvement in newborn outcomes. (Khunpradit et al. 2010). BPP is also incapable of improving outcomes; (Lalor et al. 2008) but is associated with a significant increase in induction and caesarean section. “Furthermore, the impact of the BPP on other interventions, length of hospitalisation, serious short-term and long-term neonatal morbidity and parental satisfaction requires further evaluation.” (Lalor et al. 2008)
If the fetus fails the BPP, the client is referred for Doppler assessment of blood flow in the umbilical cord, followed by Doppler assessment of both uterine arteries, and if there is any concern about those values, Doppler assessment of a middle cerebral artery of the fetus. All of these are then assessed, in conjunction with the prenatal appearance of the placenta. Each test is presumed to be safe, effective and life saving, however this presumption is not supported by irrefutable evidence of either safety or benefit . Doppler ultrasound assessment is a relatively new technique. Despite its novelty, it has been evaluated by more RCTs than any other biophysical test of fetal growth or well-being. A Cochrane review of Doppler ultrasound for high risk pregnancy trials, involving 10,000 women, (Alfirevic et al. 2010) found the evidence was of unclear quality with some evidence of possible publication bias. Uterine artery Doppler waveform analysis accurately identifies compromised fetuses at risk of stillbirth, in cases of placental underperfusion associated with pre-eclampsia and/or growth restriction, but no studies have shown any ability of subsequent intervention to prevent stillbirth. Studies of high quality with follow-up studies on neurological development are lacking. (Alfirevic et al. 2010) Cochrane review of Doppler ultrasound for low risk pregnancy found no conclusive evidence that the use of routine umbilical artery Doppler ultrasound, or combination of umbilical and uterine artery Doppler ultrasound in low-risk or unselected populations benefits either mother or baby. (Alfirevic et al 2010 #2)
Routine pregnancy ultrasound at any trimester was not associated with improvements in overall perinatal mortality. A recent meta-analysis identified nine RCTs (N = 35,049
women) which compared the outcome of perinatal mortality for ultrasound in early pregnancy versus no or selective use of ultrasound in early pregnancy (before 24 weeks) and found no significant difference between the two groups when the results were pooled. (Haws et al 2009).
There is also a need to raise concern about whether enough is known about the effects of ultrasound when used in pregnancy (Table 3). Questions should also be asked about what information is given to women related to the lack of knowledge as well as the supposed belief in its benefits.
Table 3
Potential Dangers of Prenatal Ultrasound
- It is plausible to state that there is no association between use of diagnostic ultrasound during pregnancy using commercial devices available before 1990, which use doses up to 94 mW/cm2 and childhood cancer; reduced birth weight; impaired childhood growth; and neurologic development in childhood. (Stratmeyer, et al 2008)
- Ultrasound Levels approved for use since 2002 of up to 720 mW/cm2 are 4 times higher than those tested. (Abramowicz 2008)
- Ultrasound Levels used today have never been studied epidemiologically. (Stratmeyer, et al 2008)
- First trimester is a period of high sensitivity of the fetus to teratologic insults. Ultrasound causes heat, and heat causes terotologic insults.
- Focused ultrasound is currently used to destroy kidney stones, uterine fibroids, brain tumors and small defects in spinal cord. To learn more search terms: Yoav Medan Ultrasound surgery Healing without cuts
- Sonographers have poor knowledge of thermal and mechanical effects of Ultrasound (Sheiner and Abramowicz 2008)
The role of the placenta
To date, no one has defined any placental characteristic associated exclusively with IUGR and not commonly found in normal placentas as well. This includes placental infarct and partial placental abruption. Grade III placenta, diagnosed after birth of a compromised newborn has been defined as being an indication of placental insufficiency. However, placental grading before birth has unable to identify placental grading accurately. Five highly trained, expert sonographers independently graded 90 ultrasound images either 0, I, II and III placentas on two occasions, separated by 1 week under ideal lighting conditions. (Moran et al. 2011) Consistent reporting only occurred for nine of the 90 images where they were given the same grade 0, I, II and III by all five observers. One image was graded 0, I, II and III by different sonographers. This suggests that grading of the placenta is not a reliable technique even among expert observers, although it is used to diagnose “placental insufficiency”.
Ultrasound is not accurate enough to identify deviant characteristics of the placenta in utero. Even where this is a suspicion of a placental variant, this does not enable identification of the fetus who is in danger. The most prominent and easy to identify variant of placenta is the circumvallate placenta. It has a raised white ring,
The placenta is usually examined following the birth to determine whether it can give any information about the intrauterine life it has supported for nine months, as well as assess the possibility of retained tissue. Some placentas have white circles in the fetal side of the placenta which have been given the rather nefarious sounding name of Amnion cell metaplasia or amnion nodosum. These plain white circles are present in 65% term healthy placentas (Apel-Sarid et al. 2010). Syncytial knots are protrusions from the trophoblastic surface in and amongst the placental villi, and while they sound ominous they are known to appear in 10-50% of normal terminal villi at term and are not thought to be linked to morbidity. Apel-Sarid (2010) states “The presence of increased syncytial knots in preterm Fetal Growth Restricted (FGR) neonates is probably due to exposure to hypoxia and reactive oxygen agents.” However, the paper does not define what increased means, and only found ‘increased syncytial knots” in 11% of FGR < 37 weeks, which is well within the rate for normals. Even when aiming to define placental deviations, 61% (<34 weeks) to 70% (full term) of IUGR babies born at any week delivered with a placenta lacking anything notable. (Apel-Sarid et al. 2010) The authors did not respond to my emails requesting a comment on this. Only 30% of full term and 39% < 34 weeks had one or more of the following deviations/variations present:
- Acute Chorioamnionitis
- Amnion cell metaplasia, a.c.a. amnion nodosum (present in 65% of normal placentas.
- Calcifications (not defined, no pictures)
- Infarct- focal or diffuse
- Thickening of blood vessels and poor vascularity of chorionic villi defined when terminal villi capillaries occupy less than “about” 50% of the villi volume or when <40% of capillaries were on the villous periphery.
- Increased syncytial knots (little white dots). Increased was not defined.
Salafia (1997) found that 68% of IUGR placentas had no unusual findings and 32% of the placentas born to normal term newborns had pathological placental findings present, which is similar to what was found by Apel-Sarid. To date, there is no strong evidence for being able to identify placental variations after birth that are associated with IUGR. Therefore, attempting to diagnose placental insufficiency with ultrasound examination of the placenta before the birth is ungrounded.
Conclusions
It has to be surmised that within the normal physiology of a pregnancy, the placenta will sustain the fetus until the time of birth. In the cases of partial abruptions, infarcts, or placental tumors during pregnancy, the placental villi can grow compensatory collateral blood supplies, similar to other organs in the body. An example of physiology at odds with our perception of damage and failing function is when women grow compensatory collateral blood vessels to their uterus following a trilateral uterine artery ligation to treat catastrophic hemorrhage during cesarean surgery and go on to carry subsequent pregnancies to term. (Blanc et al 2011). There is no hard evidence that either fetuses or placentas stop growing before the moment of the birth and there is some logic to support the assumption that the placenta continues to grow in the absence of factors that would inhibit this. Taken at its most basic level then, where the fetus is born alive, the placenta is definitely functioning. From this unquestionable fact, it may be thought of as incorrect to use the term dysfunctional placenta for a placenta that produces a live newborn.
Placental dysfunction is commonly named as a main cause of miscarriage at every week of pregnancy. However, for the vast majority of miscarriage, the cause is unknown and chromosomal defects that are undetectable to date are just as good an explanation as undiagnosed placental dysfunction.
Conversely, it could be that the placenta is much more involved in a whole range of events that occur during the pregnancy and in labour but that we are, at present unable to detect the extent of these and have only just begun to appreciate how or whether some of these differences may impact.
Ultrasound is documented to be horrendously inaccurate. A recent study found a full third or 34% of ultrasound fetal weight estimates to be outside of the expected +10% to – 10% range.; (Hargreaves 2011). When a fetus is suspected to be small-for-dates, there are many possible causes, but one must consider what purpose there is in making the diagnosis. The same potentially helpful behavioral, social and environmental influences that could be changed like cessation of smoking, stress management and improved nutrition can be provided in the absence of a diagnosis of IUGR.
Perhaps the hardest truth to get used to is that pregnancy is full of intricate, cleverly designed and interconnected systems without any one way to predict or control them successfully, particularly without causing more damage than one prevents, such as by routine induction or cesarean surgery. Exceptions are the rule in obstetrics. And more so when it comes to the placenta. The placenta is an incredibly dynamic and changing short lived organ and the least well studied organ in the body. I would love to see a large RCT study where one third of the women are assigned to accepted practice prenatal care with every test imaginable in the absence of any interpersonal support, another third assigned to prenatal visits in their home, with lots of nutritional, exercise and stress counseling and not a single formal prenatal test, or blood test, aside from blood type, and the remaining third provided with both. It is easy to imagine someone winning a Nobel prize for being able to predict stillbirth and prevent perinatal mortality by diagnosing a gross, easy-to-see defect of the placenta using ultrasound; but it is difficult for me to imagine a Nobel prize awarded to the person who proved that frequent home visits by the same midwife are more effective than all the prenatal testing currently known to man.
Why is more prenatal testing always the direction of prenatal care? Since cesarean increases the late third trimester stillbirth rate from 1/1000 to 1/500, why not limit cesarean to women having their last birth? We know stillbirth occurs more in the
This is an area without conflicting evidence, but rather a disconnection between accepted protocol and its ability to show benefit. It’s not a matter of confounding variables. There may be dysfunctional placentas or not, but there is no way to diagnose them during pregnancy which can then confer benefit to the mother and baby.
References
Abramowicz JS, Fowlkes JB, Skelly AC, Stratmeyer ME, Ziskin MC. Conclusions regarding epidemiology for obstetric ultrasound. J Ultrasound Med. 2008;27(4):637-44.
ACOG Practice Bulletin No. 101: Ultrasonography in Pregnancy. (2009).OBGYN 113(2):451-61.
Alfirevic Z, Stampalija T, Gyte GM. Fetal and umbilical Doppler ultrasound in high-risk pregnancies. Cochrane Database Syst Rev. 2010.20;(1):CD007529.
Alfirevic Z, Stampalija T, Gyte GM. Fetal and umbilical Doppler ultrasound in normal pregnancy. Cochrane Database Syst Rev. 2010. 4;(8):CD001450.
Apel-Sarid L, Levy A, Holcberg G, Sheiner E. Term and preterm (<34 and <37 weeks gestation) placental pathologies associated with fetal growth restriction.Arch Gynecol Obstet. 2010;282(5):487-92.
Belghiti J, Kayem G, Dupont C, Rudigoz RC, Bouvier-Colle MH, Deneux-Tharaux C. Oxytocin during labour and risk of severe postpartum haemorrhage: a population-based, cohort-nested case-control study. BMJ Open. 2011:21;1(2).
Blanc J, Courbiere B, Desbriere R, Bretelle F, Boubli L, d’Ercole C, Carcopino X. Is uterine-sparing surgical management of persistent postpartum hemorrhage truly a fertility-sparing technique? Fertil Steril. 2011;95(8):2503-6.
Fetal Ultrasound Website: http://www.fetalultrasound.com/online/text/33-020.htm
Ghidini A. Idiopathic fetal growth restriction: a pathophysiologic approach. Obstet Gynecol Surv 1996;51:376–82.
Hargreaves K, Cameron M, Edwards H, Gray R, Deane K. Is the use of symphysis-fundal height measurement and ultrasound examination effective in detecting small or large fetuses? J Obstet Gynaecol. 2011;31(5):380-3.
Harris RD, Wells WA, Black WC, Chertoff JD, Poplack SP, Sargent SK, Crow HC. Accuracy of prenatal sonography for detecting circumvallate placenta. AJR Am J Roentgenol. 1997;168(6):1603-8.
Haws RA, Yakoob MY, Soomro T, Menezes EV, Darmstadt GL, Bhutta ZA. Reducing stillbirths: screening and monitoring during pregnancy and labour. BMC Pregnancy Childbirth. 2009;9 Suppl 1:S5.
Khunpradit S, Lumbiganon P, Laopaiboon M. Admission tests other than cardiotocography for fetal assessment during labour. Cochrane Database Syst Rev. 2011;(6):CD008410.
Lalor JG, Fawole B, Alfirevic Z, Devane D. Biophysical profile for fetal assessment in high risk pregnancies. Cochrane Database Syst Rev. 2008;(1):CD000038.
Locatelli A., A. Zagarella, L. Toso, et al. 2004. “Serial assessment of amniotic fluid index in uncomplicated term pregnancies: prognostic value of amniotic fluid reduction.” J Matern Fetal Neonatal Med 15 (4): 233–6.
Magann EF, Chauhan SP, Doherty DA, Magann MI, Morrison JC.The evidence for abandoning the amniotic fluid index in favor of the single deepest pocket. Am J Perinatol. 2007;24(9):549-55.
Moran M, Ryan J, Higgins M, Brennan PC, McAuliffe FM. Poor agreement between operators on grading of the placenta. J Obstet Gynaecol. 2011;31(1):24-8.
Menticoglou SM, Hall PF. Routine induction of labour at 41 weeks gestation: nonsensus consensus. BJOG. 2002;109(5):485-91.
Nabhan AF. Abdelmoula YA. 2008. “Amniotic fluid index versus single deepest vertical pocket as a screening test for preventing adverse pregnancy outcome.” Cochrane Database Syst Rev 3:CD006593.
Salafia CM. Placental pathology of fetal growth restriction. Clin Obstet Gynecol. 1997;40(4):740-9.
Sheiner E, Abramowicz JS. Clinical end users worldwide show poor knowledge regarding safety issues of ultrasound during pregnancy. J Ultrasound Med. 2008;27(4):499-501.
Sheiner E, Sarid L, Levy A, Seidman DS, Hallak M.Obstetric risk factors and outcome of pregnancies complicated with early postpartum hemorrhage: a population-based study. J Matern Fetal Neonatal Med. 2005 Sep;18(3):149-54.
Shen O, Golomb E, Lavie O, Goldberg Y, Eitan R, Rabinowitz RR. Placental shelf – a common, typically transient and benign finding on early second-trimester sonography. Ultrasound Obstet Gynecol. 2007;29(2):192-4.
Stratmeyer ME, Greenleaf JF, Dalecki D, Salvesen KA. Fetal ultrasound: mechanical effects. REVIEW. J Ultrasound Med. 2008;27(4):597-605.
