Department of Obstetrics and Gynecology, Hospital Universitario Getafe, 28905 Madrid, Spain
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Abstract |
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Key words: early pregnancy/spontaneous abortion/trophoblast
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Introduction |
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It is estimated that of every 100 potential pregnancies only 31 progress, taking into account failures of fertilization (Barri, 1997). If we take into consideration pregnancies starting at the implantation stage, the frequency of spontaneous abortion is 3040% (Knudsen et al., 1991
; De La Fuente, 1997
). For this reason and in view of the anxiety a couple may undergo waiting for a successful outcome, many authors have studied the prognosis of pregnancy based on ultrasound criteria obtained prior to the eighth week of pregnancy.
The aim of this study was to determine the prognostic value of a new sign, the trophoblastic thickness at the embryonic implantation site, on the progression of pregnancy during the first trimester.
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Materials and methods |
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Trophoblastic thickness was recorded at each week of gestation and this was subsequently related to gestational age. The progressing of each pregnancy was followed through to week 12 to determine whether the trophoblastic thinning at the site of implantation in comparison to the gestational age in the terms described was a risk factor for spontaneous abortion.
The ultrasound scanner used was an Aloka 2000 (Tokyo, Japan) with a 10 MHz vaginal probe and a colour-coding system of blood flow in real time. The repetition frequency of pulses was 4.1 to 15 kHz. The frequency filter was placed at 50 Hz and the acoustic power (SPTA) was constantly lower than 94 mW/cm2, which is recommended by the US Food and Drug Administration, Rockville, MD, USA for the use of colour Doppler in embryo study. Maximum study time was 5 min without Doppler. The statistical analysis was carried out using the 2-test. All women were informed of the study and gave their written consent.
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Results |
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According to our data, a difference of 3 mm between gestational age (weeks) and trophoblastic thickness at the site of embryonic implantation was statistically significant (P < 0.001). When used as the only sign in predicting poor pregnancy outcome in the first trimester, it presented a sensitivity of 82%, a specificity of 93%, a positive predictive value of 63% and a negative predictive value of 97% (Table II
).
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Discussion |
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The following series of ultrasound signs found in early pregnancy predicting poor prognosis have been described: (i) gestational sac anomalies (Bromley et al., 1991; Nazari et al., 1991
; Dickey et al., 1992
); (ii) early bradycardia (Laboda et al., 1989
; May and Sturtevant, 1991
; Stefos et al., 1998
); (iii) yolk sac anomalies (Lidsay et al., 1992
; Fadda et al., 1993
; Stampone et al., 1996
; Sza1bo et al., 1996; Cepni et al., 1997
; Rempen, 1998
); (iv) subchorionic haematomas (Bennet et al., 1996
; Kurjak et al., 1996
); (v) slow embryonic growth (Koornstra and Exalto, 1991
; Bessho et al., 1995
).
Alterations of thickness, echogenicity and structure of the trophoblastic corona have always been associated with poor prognosis in pregnancy. However, as far as we can see, never before has the relationship between trophoblastic thickness at the embryonic implantation site and the gestational age in weeks been studied as a possible risk factor.
Until the seventh week of amenorrhoea, the corona has uniform thickness of 710 mm. At week 8 the trophoblast starts growing more unequally at the embryonic implantation site. Growth is progressive and, according to our study, proportional to gestational age. Consequently in those pregnancies presenting a difference between gestational age in weeks and trophoblastic thickness of 3 mm (i.e. disproportional), close ultrasound monitoring should be carried out because of greater risk of spontaneous abortion.
Nevertheless, we do not fully understand the relationship between this ultrasound sign and the subsequent loss of pregnancy although from our observations we can deduce that a decrease in thickness at the site of the future placenta could indicate `early placental insufficiency' and a placenta that cannot meet the nutritional requirements of the embryo.
In the light of our study, we consider that a difference of 3 between correct gestational age in weeks and trophoblastic thickness in mm at the embryonic implantation site should be seen as an indication that closer monitoring of the pregnancy is required since, as seen in our results, this could mean a poor outcome.
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Notes |
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References |
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Submitted on November 22, 1999; accepted on March 29, 2000.