result if the hCG level is raised by other conditions than
pregnancy. On the other hand, in case of ectopic pregnancy the hCG
level may be so low that a less sensitive test does not recognise it.
3. ULTRASOUND SCAN
This method is highly recommended, since it gives the most exact
information. However it does not release the practitioner from
performing a bimanual examination ! Since ultrasound scanners are
readily available for a moderate price they must be considered a must
in an abortion clinic. Their use prevents complications and treatment
of non pregnant women. The fact that the uterus is empty after the
procedure must be ascertained. In certain stages the termination
procedure can be monitored by ultrasound scan to avoid certain
complications.
Transducers are designed for different frequencies. With a high
frequency more details can be distinguished, but the penetration
distance is lower. An abdominal transducer therefore uses a low
frequency (3.5 Mhz). The sound beam is weakened considerably when it
passes different surfaces. Therefore a special gel is placed between
the transducer and the skin. The bladder should be full. It pushed
the bowels out of the pelvis and urine is an excellent sound
conducting medium between the transducer and the uterus. If the
uterus is mobile enough the scan can also be made (with an empty
bladder) by pushing the uterus against the abdominal wall with one
hand in the vagina and positioning the transducer with the other.
A vaginal transducer comes nearer the uterus and can therefore
work on a higher frequency, generally 7.5 Mhz. For hygienic purposes
it is covered with a condom with the gel inside. Outside the condom
an antiseptic cream may be applied to ease the introduction into the
vagina. The bladder should be empty. The ovaries and occasionally the
tubes may be recognised, so that ovarian cysts or tumours can be
diagnosed. A tubal pregnancy can be found in a young state. In a
normal intrauterine pregnancy the embryo can be recognised as early
as the fifth week. In younger pregnancies often only the amniotic
cavity and sometimes the yolk sac can be distinguished. In more
advanced pregnancies the fetus is to big to be seen completely
because the penetration of the high frequency sound is limited so
that parts of the fetus may be out of reach of the vaginal scan. If
the head of a 14 week old fetus is in the fundus it will not be
reached by vaginal scan. Modern equipment uses dual frequency
transducers which can be switched from one frequency to another
during use so that either a near object can be seen in great detail
or a far object with less detail.
The age of the pregnancy can be found accurately by measuring the
head of the fetus between both temples (BPD) or between crown and
rump (CR). BPD can be measured in pregnancies over 12 weeks, CR from
8 till about 14 weeks. Most ultrasound scan machines have a built-in
menu which calculates directly the amenorrhoea and, if the correct
date is installed, the dates of LMP and expected delivery. Appendix 4
(page 52) gives a table of the most used measurements. To measure the
BPD correctly the midline echo of the skull and the side ventricles
must be seen, otherwise a bigger diameter than the BPD is found. The
size of the amniotic cavity in a very young pregnancy is too variable
to be of any use for the estimation of the pregnancy age.
Ultrasound scan can be used to monitor the procedure. Certain
stages of the aspiration procedure may be monitored by continuous
ultrasound scan. Dr George Tiller of Wichita did so always. While an assistant keeps the transducer on the
abdomen, the surgeon sees how his instruments enter the uterine
cavity. This technique is particularly useful in the following
situations:
Two uteri sharing one cervix, described in
Chapter 11. It is often
difficult to follow the cervical canal into both hemiuteri. By
monitoring the canula can be steered into the chosen hemiuterus.
Aspiration should only be started if the canula is seen inside the
cavity.
If a perforated uterus is not empty aspiration can be continued
under continuous scan to make sure that the canula is inside the
uterus if vacuum is applied.
Chapter 12.