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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5786_Библиотеки_им_академика_М_И_Перельмана.pdf
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Examining the cervix by transvaginal ultrasound
Kjell Å Salvesen Sturla H Eik-Nes
ABSTRACT
Transvaginal ultrasound identifies women with high risk of preterm delivery.
Cervical funnelling is associated with spontaneous preterm birth. A short cervix is
commonly defined as a cervix <25 mm at 20–24 weeks of gestation. Sonographic
measurement of the cervical length can help the clinician to distinguish between
true and false labour. Of all women with a short cervical length, in only a minority
will this be due to cervical incompetence.
KEYWORDS
Cervical funnelling, cervical incompetence, cervical length, preterm labour.
INTRODUCTION
Preterm birth (PTB) is the leading cause of neonatal morbidity and mortality,
and is responsible for half of all neonatal deaths. Mortality rises from about 2%
for infants born at 32 weeks to more than 90% for those born at 23 weeks.1
Moreover, handicap or disability arises in about 60% of survivors after birth at
26 weeks and 30% in those born at 31 weeks.2 Furthermore, preterm birth is
associated with a huge cost to the health service because of the need for neonatal intensive care and the continuing support necessary after discharge from the
hospital.
These include preterm labour (PTL), preterm prelabour rupture of membranes
(PPROM) and indicated or iatrogenic preterm delivery (PTD). PTL is defined
as uterine activity that leads to cervical effacement and dilation in the absence
of PPROM. PPROM is defined as rupture of membranes >1 hour prior to uterine contractions (<37 weeks). Iatrogenic PTD is delivery secondary to maternal
3
There are three recognized aetiological categories that result in preterm birth.
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Preterm birth
Multiples
Delivery secondary
to maternal and
fetal complications
latrogenic deliveries Spontaneous deliveries
Preterm prelabour
rupture of
membranes
Preterm labour
(PTL)
Deliveries
Fetal anomalies
and IUDF
10%
1
3
10%80%
1
3
1
3
Fig. 8.1 Causes of preterm birth.
and fetal complications of pregnancy. The three aetiological categories are each
responsible for around one-third of preterm births in singleton pregnancies without malformation or intrauterine fetal death (Fig. 8.1).
Ultrasound in obstetrics and gynaecology
The processes that lead to both term and preterm spontaneous labour resemble an inflammatory reaction. Upregulation of inflammatory cytokines and prostaglandins that occurs over a period of several weeks leads to cervical ripening
and membrane rupture (PROM). This will again lead to myometrical contractility and labour. Ascending infection is likely to be an aetiological factor. The cervix
acts as a barrier to this stimulus, maintaining the distance from the vagina and
retaining the cervical mucus plug. Women with a short cervix will be at much
greater risk of this cervical barrier being breached. Once inflammation has been
stimulated, cervical ripening will occur, which will lead to shortening and funnelling of the cervix. A ‘vicious circle’ will ensue, in which further ascending infection causes increased inflammation.
TRANSVAGINAL ULTRASOUND OF THE CERVIX PREDICTS PRETERM DELIVERY
Transvaginal ultrasound is superior to digital examination and to translabial, transperineal or transabdominal ultrasound in evaluating the uterine cervix. It is well
accepted by pregnant women and provides high-quality images of the cervix.
Transvaginal ultrasound of the cervix enables us to identify women at high risk
of preterm delivery. The shorter the cervical length, the higher is the risk of preterm delivery and vice versa. A screening study at 22–24 weeks has shown that
the risk for spontaneous early preterm delivery increases with decreasing cervical
length, from about 0.2% at 60 mm to 1.1% at 25 mm, 4.0% at 15 mm and 78%
at 5 mm.4 Furthermore, demographic characteristics and obstetric history did not
134
have a substantial additional contribution to that of cervical length in the prediction of preterm delivery.
Funnelling is the protrusion of membranes into the endocervical canal. Zilanti
et al6 suggested that the cervix should be classified according to the shape of the
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funnel, and they suggested the mnemonics T, Y, V, U to denote the relationship
of the internal os to the lower segment and cervix. Figure 8.2 demonstrates a
V-shaped funnel of cervix in a transvaginal scan at 31 weeks. Iams has suggested
that funnelling is nothing but effacement of the cervix:
The process, called funnelling when it occurs in the second and early third trimesters,
is actually effacement in progress. It is dynamic, in that the internal os is seen to open
and close in the absence of palpable uterine contractions. It is probably normal after
32 weeks.
7
Berghella et al8 found that the prevalence of preterm birth before 35 weeks
of gestation was significantly higher in women with a short cervical length
when funnelling was present. In a logistic regression, controlling for cervical
length, funnelling remained associated with spontaneous preterm birth before
35 weeks.8 However, a cervix with funnelling is always short. Thus, the length
of the closed cervix has proven to be the single most important measurement
in predicting preterm delivery. Funnelling does not seem to add further clinical
information.
9
Cervical length was normally distributed in 2702 women attending ultrasound
at 23 pregnancy weeks at King's College Hospital in London. The median value
was 38 mm, and the fifth and first centiles were 23 mm and 11 mm respectively.
4,5
The cervical length was <25 mm in 8.1% and <15 mm in 1.6% of women at 23
weeks of pregnancy. Cervical length was significantly shorter in women of AfroCaribbean origin compared to Caucasians, those less than 20 years of age, and
those who had previous midtrimester losses or preterm delivery.
4,5
A similar distribution of cervical length was found in a study of 2915 US
women.10 The mean cervical length at 24 weeks was 34 mm for nulliparous
women and 36.1 mm for parous women, and the 10th centile was 26 mm and
the fifth centile was 22 mm.10 A Finnish study of 3694 singleton pregnancies
between 18 and 22 weeks found a mean cervical length of 40.7 mm and the third
Examining the cervix by transvaginal ultrasound
Fig. 8.2 Cervical incompetence with V-shape funnel. Transvaginal scan, 31 weeks.
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centile was 29 mm.11 Based on these studies, a short cervix is commonly defined
as <25 mm (10th centile) at 20–24 weeks. A cervix <15 mm will only occur in
around 1% of the pregnant population, but the risk of preterm delivery increases
exponentially below this length.
MEASUREMENT TECHNIQUE
The cervix should be examined with transvaginal ultrasound in a standardized
way to allow comparison with results from previous studies and to use the measurements for clinical judgement. The recommended standardized procedure is:
after patient voiding
•
no pressure on the cervix
•
identify the internal and external os in a sagittal view
•
apply gentle suprapubic or fundal pressure
•
measure the length of the closed cervix (do not trace)
•
measure three times – use the minimum.
Ultrasound in obstetrics and gynaecology
•
Measurement of the length of the closed cervix is demonstrated schematically in
Figure 8.3.
TRANSVAGINAL ULTRASOUND OF THE CERVIX IN THE CLINICAL JUDGEMENT OF PRETERM LABOUR
Transvaginal ultrasound of the cervix can be used in clinical judgement of preterm
labour. The Oracle II randomized trial enrolled 6295 women in spontaneous preterm labour with intact membranes and without evidence of clinical infection.12
In the placebo group with no treatment (n=1556 women), 85% were undelivered
after 7 days. This is in accordance with the clinical experience in most obstetric
units. There is an overuse of tocolytic drugs to allow for treatment with corticosteroids for lung maturation. Sonographic measurement of the cervical length can
help the clinician to distinguish between true and false labour.
136
Fig. 8.3 Schematic drawing of a measure of cervical length. A straight line is drawn from
the internal to the external os.
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In a study involving 216 women with singleton pregnancies presenting with regular and painful uterine contractions at 24–36 weeks of gestation, spontaneous delivery within 7 days occurred in only 1/173 with cervical length >15 mm, compared to
16/43 (37%) with cervical length <15 mm.13 Thus, if clinicians are in doubt about
true or false labour, they can rely on ultrasound measurements of the cervix.
This is also true for PPROM. In a study of sonographic measurement of cervical length in PPROM at 24–36 weeks including 101 women with singleton
pregnancies, delivery within 7 days of presentation occurred in 58/101 (57%)
pregnancies.14 Logistic regression analysis demonstrated that significant independent contribution in the prediction of delivery within 7 days was provided by
cervical length (odds ratio 0.91, 95% CI 0.86–0.96), gestational age at presentation (odds ratio 1.35, 95% CI 1.14–1.59) and presence of contractions (odds ratio
3.07, 95% CI 1.05–8.92).
14
TREATMENT OF CERVICAL INCOMPETENCE
A short cervical length on ultrasound has become synonymous with cervical
incompetence. However, any woman who is going to suffer from a spontaneous preterm delivery will develop a short cervix. Thus, a short cervix does not by
itself indicate cervical incompetence.
incompetence lies in differentiating this condition from other causes of early preterm delivery and pregnancy loss. ‘True’ cervical incompetence is believed to be
responsible for less than 10% of PTB, but it can be effectively treated by a surgical
procedure: cervical cerclage.
Figure 8.4 demonstrates an ultrasound picture of an incompetent cervix with
a cervical suture ad modum MacDonald.
15
The critical importance of clinical cervical
Examining the cervix by transvaginal ultrasound
Fig. 8.4 Cervical incompetence treated with cerclage ad modum MacDonald. Transvaginal
scan, 28 weeks. The suture can be seen as white spots within the cervical tissue
approximately 1.5 cm above the external os.
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Randomized clinical cerclage trials in women at high risk of preterm delivery,
and even meta-analysis of cerclage trials, present conflicting results.
16,17
explanation for these results may be suboptimal patient selection. A more effective way of identifying a high-risk group would be by transvaginal sonographic
measurement of cervical length.
To et al18 screened cervical length in 47,123 women between 22 and 25 pregnancy weeks. The cervix was 15 mm or less in 470 women. In all, 253 (54%) of
these women were randomized to have a cervical cerclage (n=127) or to expectant management (n=126). The proportion of preterm delivery before 33 weeks
was similar in both groups, 22% in the cerclage group versus 26% in the control
group (relative risk 0.84, 95% CI 0.54–1.31), with no significant differences in
perinatal or maternal morbidity or mortality.
There is a common misunderstanding that this trial demonstrates that cervical
cerclage does not prevent preterm birth in women with short cervix. This is not
correct. The trial demonstrates that ultrasound screening for short cervix in lowrisk women, followed by therapeutic cerclage, does not prevent preterm birth.
Ultrasound in obstetrics and gynaecology
Simcox et al19 advocate caution against extrapolation of the findings of this trial
to women with a history of previous midtrimester or preterm delivery. Furthermore,
they state that one rationale for the cerclage is to minimize ascending infection by
preventing membrane exposure and indicate that inserting a cerclage at a cervical
length of 15 mm might be too late.19 To et al, however, argue against decreasing
the threshold for cerclage to 20 mm or 25 mm.20 This would result in a threefold
and sevenfold increase, respectively, in the screen-positive rate, and subject many
women with a very low risk of preterm delivery to a surgical procedure.
A possible
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PROPHYLACTIC CERCLAGE OR TRANSVAGINAL FOLLOW-UP OF THE CERVIX
One important question is whether women at high risk should be subject to prophylactic cerclage or transvaginal ultrasound follow-up of the cervix. This has not
been formally tested in randomized controlled trials, but there is some evidence
from observational studies.
Groom et al21 performed a matched case–control study of women with a history of preterm birth, second-trimester loss or cervical surgery. Women either
received a prophylactic cerclage or were followed up with measurements of cervical length and had therapeutic cerclage, if necessary. A short cervical length was
found in 14 of 39 women (36%) in the follow-up group. No differences were
found between the groups.
Higgins et al22 performed a prospective cohort study of high-risk women. Women
were managed according to the obstetric unit to which they were referred. Some
of the obstetric units used elective cerclage, and some used therapeutic cerclage
after ultrasound follow-up. A short cervix before 24 weeks of gestation was found
in 12 of 38 women (32%) in the follow-up group, who were subsequently treated
with therapeutic cerclage. Preterm delivery before 30 weeks was significantly more
common in the prophylactic cerclage group (19% versus 2.6%, p=0.03).
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The two studies suggest that therapeutic cerclage after ultrasound follow-up
seems to be a better policy than prophylactic cerclage. However, firm conclusions
cannot be drawn from observational studies. Randomized controlled trials should
be done.
PROPHYLACTIC TREATMENT WITH PROGESTERONE IN PREGNANT WOMEN WITH SHORT CERVIX
Progesterone is a key hormone in the onset of labour in many animal species, but
its role in human labour is uncertain. Prophylactic treatment with progesterone to
prevent preterm birth is debated. A Cochrane review from 2006 suggests that prophylactic progesterone may halve the incidence of preterm births.23 A randomized
controlled trial from 2007 demonstrated that for women with a short cervix
(<15 mm) at 23 weeks, prophylactic treatment of 200 mg progesterone per day applied
vaginally reduced preterm birth rate before 34 weeks from 34% to 19%.24 A randomized controlled trial of twin pregnancies demonstrated no beneficial effects of
prophylactic progesterone injections.25 It is possible that the mechanisms for preterm birth in multiple pregnancies are different from singleton pregnancies.
There are reasons to believe that prophylactic use of progesterone will be a
future treatment option for women without a history of previous poor obstetric
outcome, singleton pregnancy and a short cervix in mid-pregnancy. Women with
previous poor obstetric outcome and a short cervix may possibly benefit from
therapeutic cerclage. However, it should be pointed out that this treatment strategy
needs further support from classical evidence based studies.
Examining the cervix by transvaginal ultrasound
CONCLUSION
Transvaginal ultrasound identifies women at high risk of preterm delivery. Cervical
length is related to the risk of preterm delivery. Previous late abortion(s) and/or
extreme preterm birth(s) in combination with a short cervix in mid-pregnancy is
suggestive of cervical incompetence. These women should be treated by cervical
cerclage. Prophylactic use of progesterone may be a future treatment option for
women with short cervix and no previous poor obstetric outcome.
References
1. Draper ES, Manktelow B, Field DJ,
James D. Prediction of survival for preterm
births by weight and gestational age:
a retrospective population based study. BMJ
1999;319:1093–1097
2. Koppe JG, Verloove-Vanhorick PSP, Ilsen
A. Long-term outcome. In: Kurjak A (ed)
Textbook of perinatal medicine. Parthenon,
Carnforth, 1998: 1362–1374
3. Petrou S. Economic consequences of
preterm birth and low birth weight. Br J
Obstet Gynaecol 2003;110:17–23
4. Heath VCF, Southall TR, Souka AP,
Elisseou A, Nicolaides KH. Cervical
length at 23 weeks of gestation: prediction
of spontaneous preterm delivery.
Ultrasound Obstet Gynecol 1998;12:
312–317
5. Heath VCF, Southall TR, Souka AP,
Novakov A, Nicolaides KH. Cervical
length at 23 weeks of gestation: relation to
demographic characteristics and previous
obstetric history. Ultrasound Obstet
Gynecol 1998;12:304–311
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6. Zilanti M, Azuaga A, Calderon F, Pages G,
Mendoza G. Monitoring the effacement of the
uterine cervix by transperineal ultrasound.
J Ultrasound Med 1995;14:719–724
7. Iams JD. Cervical ultrasonography.
Opinion. Ultrasound Obstet Gynecol
1997;10:156–160
8. Berghella V, Pereira L, Gareipa A, Simonazzi
G. Prior cone biopsy: prediction of preterm
birth by cervical ultrasound. Am J Obstet
Gynecol 2004;191:1393–1397
9. To MS, Skentou C, Liao AW, Cacho
AM, Nicolaides KH. Cervical length and
funneling at 23 weeks of gestation in the
prediction of spontaneous early preterm
delivery. Ultrasound Obstet Gynecol
2001;18:200–203
10. Iams JD, Goldenberg RL, Meis PJ et al.
The length of the cervix and the risk of
spontaneous premature delivery. N Engl J
Med 1996;334:567–572
11. Taipale P, Hillesmaa V. Sonographic
Ultrasound in obstetrics and gynaecology
measurement of uterine cervix at 18–22
weeks' gestation and the risk of preterm
delivery. Obstet Gynecol 1998;92:902–907
12. Kenyon SL, Taylor DJ, Tarnow-Mordi W
and the ORACLE Collaborative Group.
Broad-spectrum antibiotics for spontaneous
preterm labour: the ORACLE II randomised
trial. Lancet 2001;357:989–994
13. Tsoi E, Akmal S, Rane S, Otigbah C,
Nicolaides KH. Ultrasound assessment of
cervical length in threatened preterm labor.
Ultrasound Obstet Gynecol 2003;21:552–555
14. Tsoi E, Fuchs I, Henrich W, Dudenhausen
JW, Nicolaides KH. Sonographic
measurement of cervical length in preterm
prelabor amniorrhexis. Ultrasound Obstet
Gynecol 2004;24:550–553
15. Williams M, Iams JD. Cervical length
measurement and cervical cerclage to
prevent preterm birth. Clin Obstet Gynecol
2004;47:775–783
16. Bachmann LM, Coomarasamy A, Honest
H, Khan KS. Elective cervical cerclage for
prevention of preterm birth: a systematic
review. Acta Obstet Gynecol Scand
2003;82:398–404
17. Drakeley AJ, Roberts D, Alfirevic Z.
Cervical stitch for preventing pregnancy
loss in women. Cochrane Database of
Systematic Reviews 2003, Issue 1. Art No.
CD003253
18. To MS, Alfirevic Z, Heath VCF et al.
Cervical cerclage for prevention of
preterm delivery in women with short
cervix: randomised controlled trial. Lancet
2004;363:1849–1853
19. Simcox R, Bennett PR, Shennan AH.
Cervical cerclage for prevention of preterm
delivery in women with short cervix. Lancet
2004;364:1934–1935
20. To MS, Alfirevic Z, Williamson PR,
Nicolaides KH. Cervical cerclage for
prevention of preterm delivery in women
with short cervix: randomized controlled
trial. Authors' reply. Lancet 2004;364:1935
21. Groom KM, Bennett PR, Golara M et al.
Elective cervical cerclage versus serial
ultrasound surveillance of cervical length
in a population at high risk for preterm
delivery. Eur J Obstet Gynecol Reprod Biol
2004;112:158–161
22. Higgins SP, Kornman LH, Bell RJ,
Brennecke SP. Cervical surveillance as an
alternative to elective cervical cerclage
for pregnancy management of suspected
cervical incompetence. Aust NZ J Obstet
Gynecol 2004;44:228–232
23. Dodd JM, Flenady V, Cincotta R et al.
Prenatal administration of progesterone
for preventing preterm birth. Cochrane
Database Syst Rev 2006; (1): CD004947
24. Fonseca EB, Celik E, Parra M et al.
Progesterone and the risk of preterm birth
among women with a short cervix. N Engl J
Med 2007;357:462–469
25. Rouse DJ, Caritis SN, Peaceman AM et al.
A trial of 17 Alpha-hydroxyprogesterone
caproate to prevent prematurity in twins.
N Engl J Med 2007;357:454–461
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Fetal biometry, estimation of gestational age, assessment of fetal growth
Domenico Arduini Francesco Giacomello
ABSTRACT
The aims of ultrasound fetal biometry are: (1) the estimation of true gestational
age, (2) the prediction of day of delivery, (3) the diagnosis of growth disturbances
and (4) the diagnosis of malformations. The correct methodology for sonographic
measurement of the essential fetal parameters is reported. Basic statistical analysis
for defining normal values and nomograms is indicated. Principles for pregnancy
dating and limits of the sonographic evaluation of fetal growth disturbances are
reported and discussed.
KEYWORDS
Fetal biometry, fetal growth restriction, macrosomia, ultrasound.
PRINCIPLES OF FETAL BIOMETRY
AIMS OF FETAL BIOMETRY
A significant increase in perinatal morbidity and mortality is recorded for infants
born either large or small for their respective age. Fetal biometry has enhanced the
ability to detect growth abnormalities, thus directing more intensive antepartum
care with potential improvement in perinatal outcome.
fetal biometry prior to 20 weeks' gestation provides an accurate dating, allowing more confident diagnoses of growth abnormalities and prediction of neonatal
survival in case of premature delivery. Finally, the abnormality of some biometric
parameters may indicate the presence of congenital malformations or syndromes.
Therefore the aims of fetal biometry are the following: the assessment of true gestational age, the prediction of day of delivery, the diagnosis of fetal growth disturbances, and the diagnosis of fetal malformations and chromosomal syndromes.
14,16,22
In addition, routine
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THE REFERENCE VALUES
Many tables and nomograms have been published describing the growth of many fetal
parameters.
2,10
The normal values are defined by measuring the required parameter
in fetuses of normal patients with a well-established gestational age (GA).
PATIENT SELECTION AND STUDY DESIGN
To study the growth of fetal parameters, the date of conception should be certain but this information is available only in cases of treatment for infertility.
A well-accepted way of dating the pregnancy is regular cycles, a well-defined last
menstrual period (LMP), and a confirmation with early ultrasound. The ideal population should be selected among uncomplicated pregnancies delivered at term.
LONGITUDINAL AND CROSS-SECTIONAL STUDIES
Data collection could be cross-sectional or longitudinal. In a cross-sectional study
Ultrasound in obstetrics and gynaecology
the fetus is measured only once during gestation, whereas in a longitudinal study
it is measured serially at regular intervals. Cross-sectional studies are usually performed over a shorter period of time with easier collection of data and statistical
analysis because each patient needs to be scanned only once. Then the individual
growth is missed in favour of a larger population cohort. Common pitfalls for the
cross-sectional studies are the occasional inclusion of fetuses with abnormal growth
and/or poorly established GA, follow-up problems due to the large number of
cases involved, and frequent artefacts concerning values at early and late gestation.
An essential rule for cross-sectional studies is that each fetus should be considered
only once in the study and that violation of this principle may severely affect the
accuracy of the final results. In longitudinal studies one should define GA in early
pregnancy and control the established criteria in fewer patients with easy recognition of abnormal growth curves. Such studies require the recruitment of a small
number of pregnant women, scanned at regular intervals, and their results are often
favoured with mathematical, biological and epidemiological arguments.
14
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SAMPLE SIZE
The optimal sample size depends on the variability of the parameter under investigation. Small samples preclude the use of polynomial regression whereas very
large samples do not decrease the standard deviation significantly but increase the
difficulty of follow-up data due to the probability of including data from abnormal cases. The sample should be well distributed throughout gestation with the
same number of observations throughout the range of inclusion.
14
DISPLAYING DATA AND CURVE FITTING
The data collected are represented in graph form, plotting the variable on the
y-axis and the GA at which the data were obtained on the x-axis. The resulting