Human Reproduction, Vol. 14, No. 2, 556-559,
February 1999
© 1999 European Society of Human Reproduction and Embryology
Case Report: Can nuchal cord cause transient increased nuchal translucency thickness?
Department of Obstetrics and Gynecology, Assaf Harofe Medical Center, Zrifin, 70300 (affiliated with Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv), Israel
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Abstract |
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When detected in a first trimester scan, an increased thickness of nuchal translucency (NT) may be associated with chromosomal, cardiac or genetic disorders. However, less attention has been devoted to the outcome of those fetuses who have confirmed normal anatomies and karyotyping, but have abnormal first trimester scans. Thus, a challenging new issue is how to counsel such cases of transient increased NT in which the translucency rapidly vanishes with no evidence of other underlying abnormalities. Two cases of transient increased thickness of NT are reported. In both, a nuchal cord was ultrasonographically demonstrated and a thorough work-up revealed chromosomally and anatomically normal fetuses. The pathophysiological theories behind these observations and their significance are discussed. Based on these observations, we suggest that transvaginal sonography combined with Doppler flow studies should be utilized for the presize detection of cord patterns to accomplish the work-up in cases of increased NT.
Key words: Doppler flow/nuchal cord/nuchal translucency/pregnancy/sonography/transient appearance
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Introduction |
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First trimester ultrasound offers the advantages of identifying and measuring small subcutaneous collections of fluid behind the fetal back and neck (Szabo and Gellen, 1990
), known as nuchal translucency (NT) (Pandya et al., 1995). The association between increased NT, chromosomal abnormalities (Ville et al., 1992; Snijders et al., 1996, 1998; Taipale et al., 1997), cardiac and other anatomical defects (Cha'bam et al., 1996; Hyett et al., 1997a; Montenegro et al., 1997) as well as some genetic syndromes (Hyett et al., 1997b; Reynders et al., 1997; Souka et al., 1998) are well documented. Occasionally, there are cases exhibiting markedly increased NT which resolve spontaneously within 10–14 weeks of gestation (Pajkrt et al., 1995; Fukada et al., 1997). The significance of this `transient appearance', and a reasonable explanation for its occurrence, are not thoroughly addressed in the literature. Two cases are reported of normal fetuses with increased NT, which resolved spontaneously before 14 weeks. In both cases, the finding of a nuchal cord may be associated with this `transient appearance' phenomenon.
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Case report |
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Case 1
A 28 year old primigravida woman was referred to our unit for first trimester ultrasound screening at 12 weeks and 4 days of gestation. Past medical and familial histories of the couple were unremarkable and they were not consanguineous. Nuchal translucency measurement was performed according to Nicolaides et al. (1992), using software developed for Down's syndrome risk assessment. The risk was calculated on the basis of maternal age and gestational age-related prevalence, multiplied by the likelihood ratio depending on the deviation from normal in NT thickness for crown–rump length (Nicolaides et al., 1992
; Snijders et al., 1996, 1998).
A transabdominal scan (4 MHz curvilinear abdominal transducer: Advanced Technology Laboratories, HDI 3000, Seattle, WA, USA) revealed a singleton fetus with a heart beat of 170 bpm and crown–rump length (CRL) of 47 mm, appropriate for 11 weeks and 5 days. NT thickness was 2.9 mm, which increased the risk of having a Down's syndrome newborn to 1 in 220. At that stage, no other ultrasonographic gross abnormalities or signs of hydrops were noticed. However, the appearance of a nuchal cord was observed (Figure 1A). On a repeat scan 6 days later, the increased NT had regressed significantly and no signs of a nuchal cord were detected (Figure 1B). Nevertheless, the patient underwent amniocentesis for karyotyping, detailed anomaly scanning and echocardiography. These examinations were normal and the patient was carefully followed until spontaneous term delivery of a normal infant.
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Case 2
A 32 year old woman (gravida 3, parous 2) was referred at 12 weeks and 4 days of gestation to our unit for first trimester ultrasound screening. The past medical and familial histories of the couple were unremarkable and they were not consanguineous.
A transabdominal scan revealed a singleton fetus with a heart beat of 167 bpm, CRL of 51 mm, appropriate for 11 weeks and 6 days gestation, and NT thickness of 4 mm. No other fetal anatomical abnormalities or hydrops were ultrasonographically detected. A detailed transvaginal examination (using a 9 mHZ transvaginal transducer), and Doppler flow scans were performed which demonstrated a nuchal cord (Figure 2A, B). The increased NT thickness heightened the risk of having a Down's syndrome newborn to 1 in 12. Four weeks later, the patient was rescanned; the increased NT had completely vanished and the nuchal cord was no longer demonstrated (Figure 2C). The patient was offered amniocentesis for karyotyping, detailed anomaly scanning, and echocardiography, all of which were completely normal. This patient was carefully followed until spontaneous term delivery of a normal infant.
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Discussion |
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The presence of skin elevation in the posterior and lateral neck region of aborted human fetuses was first reported in the 19th century (Steinwirker, 1872
). The advancement of ultrasonographic techniques has made earlier detection of such nuchal membranes feasible; appearing as hypoechogenic areas beneath the skin and outside the tissue covering the cervical vertebral column (Szabo and Gellen, 1990; Nicolaides et al., 1992; Cha'bam et al., 1996; Snijders et al., 1996; Hyett et al., 1997a,b; Montenegro et al., 1997; Reynders et al., 1997; Taipale et al., 1997). Although this sonographic feature is well described, accurate documentation of the pathophysiological and morphological basis of such a phenomenon is still uncertain. During early fetal life, the lymphatic vessels drain into two large sacs in the nuchal area connected to the jugular vein system. As a result, NT is physiologically and ultrasonographically detectable from gestational week 7, and generally resolves within the first trimester (Fukada et al., 1997).
Increased fluid accumulation has been reported in fetuses with Turner's syndrome, and includes cystic hygroma, which characteristically contains fluid-filled cavities. The aetiology of this formation is believed to be caused by abnormal lymphatic development or local lymphatic vessel aplasia interrupting their drainage into the jugular lymph systems (Chervenak et al., 1983; Brand-Saberi et al., 1994). The fluid then collects in the posterior neck fold, causing the ultrasonographic appearance of a septated or non-septated nuchal cystic hygroma. As the pregnancy continues, the fluid collection may resolve and a thick nuchal fold ensues (Chervenak et al., 1983).
In trisomy 21, the increased NT is explained by the subcutaneous accumulation of fluid in the neck of the fetus. In such cases, interstitial fluid has been found to be bound to collagen subtype IV, leading to a swelling of the fetal derma, including the nuchal and leg skin (Brand-Saberi et al., 1994). Another feature more commonly occurring in trisomy 21 fetuses is the alteration in fetal haemodynamics due to early heart failure, secondary to cardiac and/or great artery abnormalities (Hyett et al., 1997a; Montenegro et al., 1997). Primarily, this is a narrowing of the aortic isthmus which has been found at postmortem examination to be a common finding in fetuses with increased NT (Hyett et al., 1995, 1997a). These can be attributed to temporary strain caused by a high proportion of cardiac output narrowly diverted to the head and neck (Hyett et al., 1997a) either alone or in combination with an increase in mRNA expression of atrial natriuretic peptide and brain natriuretic peptide in trisomic fetuses (Hyett et al., 1996).
The `transient appearance' has been occasionally documented by sonographers performing first trimester scanning and screening (Pajkrt et al., 1995; Fukada et al., 1997; Huisman and Bilardo, 1997).
Although a large amount of data has been accumulated concerning the risk of chromosomal and organ abnormalities in fetuses with increased nuchal thickening, less attention has been given to the outcome of those fetuses who have confirmed normal anatomies and karyotyping, but have abnormal first trimester scans. With respect to these data, and the recent report that ~60% of fetuses with increased NT have adverse outcomes, regardless of its resolution (Fukada et al., 1997), additional information is needed to help counsel those patients. This need is especially reinforced due to the observation that spontaneous resolution of increased NT may occur and the only explanation which has been proposed is the correction of the haemodynamic disturbances occurring later in gestation (Hyett et al., 1997c; Huisman and Bilardo, 1997). Assuming that there is an association between transient NT thickness and the nuchal cord, we can speculate on two differing pathophysiological mechanisms: 1) a local effect of the cord causing disruption of the head and neck lymphatic drainage system, or 2) the tied cord alone may produce some narrowing of the cord vessels leading to transient heart failure, followed by neck congestion. These theories should be further studied to clarify a more precise pathophysiological explanation. In this respect, it is significant that other authors have focused on the nuchal cord between 10–14 weeks of gestation, reporting that such a phenomenon can be detected in ~8% of the screened fetuses (Schaefer et al., 1998). They also used Doppler flow for more accurate determination of the cord pattern. However, their main concern was to avoid the 1–2 mm of the cord added to the ultrasound measurement, thus reducing the false positive results (Schaefer et al., 1998).
The problem with such a `soft ultrasonic marker' is that even when common abnormalities have been ruled out, both the pregnant woman and her obstetrician will still be concerned as to their significance. Thus, information gained through ultrasound permits some hope. In cases of increased NT, we agree with other authors (Schaefer et al., 1998) who perform detailed transabdominal and transvaginal scannings, coupled with Doppler flow studies for visualizing the cord pattern: and should be follow-up scans. When the cord is visualized as encircling the fetal neck, i.e. a nuchal cord, it could be considered as a reassuring sign, providing another pathophysiological explanation, and avoiding a false positive measurement of the nuchal cord added to the NT. This occurs mainly when the translucency disappears and no other fetal anatomical or chromosomal abnormalities are detected.
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Acknowledgments |
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The authors thank Sally Esakov for her editorial assistance.
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Notes |
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1 To whom correspondence should be addressed
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Submitted on May 13, 1998; accepted on November 18, 1998.
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