Cesarean scar pregnancy (CSP) consists of implantation of
the gestational sac in the previous hysterotomy scar, with some serious complications
as the pregnancy progresses.
CSP was first described by Larsen and Salomon in 1978. The
incidence currently is 1/1800 to 1/2200 pregnancies with 0.15% of women with
previous Caesarean sections ending in CSP. But, as the rates of cesearean section
rates are increasing world wide, with some countries reporting as high as 50%,
the incidence of CSPs is bound to increase!
Risk factors for CSPs
are those with a history of multiple
Caesarean sections and Caesarean breech delivery but scar pregnancies have also
been reported after dilation and curettage, myomectomy, metroplasty,
hysteroscopy, and manual removal of the placenta.
In fact up to 72% of cesarean scar pregnancies occur in
women who have had 2 or more cesarean deliveries.
Transvaginal Sonography and color Doppler are the best
diagnostic tools at present, but the clinician should have a high index of
suspicion to use them.
According to a paper by Osborn D.A et al the following sonographic criteria have been put forward for
early diagnosis of cesarean scar pregnancies in the first trimester.
- Empty uterus with a clearly visualized endometrium;
- Empty cervical canal;
- Gestational sac within the anterior portion of the lower uterine segment at the presumed site of the cesarean scar; and
- Thinned or absent myometrium between the gestational sac and bladder (<5 mm in two-thirds of cases).
- Other findings include marked peritrophoblastic color Doppler flow around the sac with low-impedance (pulsatility <1), high-velocity flow (>20 cm/s), a resistive index of less than 0.5, and a peak systolic to diastolic blood flow ratio of less than 3.
MRI being useful as a troubleshooting tool when sonography
is equivocal or inconclusive before intervention or therapy.
This paper by Timor-Tritsch I.E et al in the forthcoming
issue of American Journal of Obstetrics &
Gynecology describe a sonographic method for the differential diagnosis
of CSP vs IUP in early gestation.
The study tests the hypothesis that in a first trimester sonography
between 5-10 weeks of pregnancy the relative location of the center of
gestational sac to the midpoint of the uterus along a longitudinal line between
the external cervical os and the fundus can be used for early detection of CSPs.
This is a retrospective study reviewing the electronic
record of 242 ultrasound images from 20004- 2015 were analyzed. A total of 57
cases of CSP diagnosed. The following measurements were made for each case:
- distance from the external cervical os to the uterine fundus,
- the midpoint axis of the uterus,
- the distance from the external cervical os to the center of gestational sacs, and
- the distance from the external cervical os to the most distant edge of the gestational sacs from the cervix.
It was seen that the location of the center of gestational
sac relative to the midpoint axis of the uterus between 5-10 weeks of gestation
differentiated between IUP and CSP (mean 17.8 vs –10.6 mm, respectively, P =
.0001).
Most CSPs are located proximally to the midpoint axis of the
uterus and most IUPs are located distally to the midpoint axis.
The diagnostic accuracy of the method: accuracy: sensitivity 93.0% and specificity 98.9%.
The diagnostic accuracy of the method: accuracy: sensitivity 93.0% and specificity 98.9%.
The authors strongly believe that the mounting anecdotal
evidence supports instituting a simple, relatively inexpensive very early
transvaginal screening ultrasound of every pregnant patient with a previous
history of cesarean delivery.
References:
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