an overview of the uterine anatomy with clinical implications with regards to placenta praevia

1. NurFakhriyyah, LokemanHazli, Alia Nadhirah
Associate Professor Dr Hanifullah Khan
1 03/23/12

2. * This presentation aims to
* Explain what the Lower Uterine Segment (LUS) is
* An outline of it’s anatomical and histological
features
* The implications of the LUS in clinicalpractice
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3. * Uterine enlargement in pregnancy
* by hypertrophy, hyperplasia and stretching of the
muscle fibres.
* from 50-60g to almost 1000g at term
* At 7 weeks - the size of an egg;
* At 10 weeks it is the size of an orange and fills the
entire pelvis.
* At 12 weeks it rises out the pelvis and palpable
abdominally just above the symphysis pubis
3 03/23/12

4. * The lower uterine segment
(LUS) is the part of the
uterus and the upper cervix
which lies between the
attachment of the
peritoneum of the
uterovesical pouch
superiorly & the internal
cervical os inferiorly.
* The isthmus of the uterus,
the lower extremity of
which joins with the
cervical canal and during
pregnancy expands to
become the lower part of
the uterine cavity
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5. * With increasing gestation, there is increased
stretching of the uterine muscle fibres.
* This results in the formation of the lower segment in
the 3rd trimester (28 – 40 weeks).
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6. 6 03/23/12

7. * This part of the uterus is
thinner contain less
muscle fibres and blood
vessels.
* This is the site for
caesarean section incision.
* The placenta is attached
to the more vascular and
thicker upper segment.
7 03/23/12

9. * In such cases, the placenta is
attached partially or
completely to the LUS
* Placental a t t a c h m e n t
i s d i s r u p t e d as this
area gradually thins in
preparation for the onset of
labor.
* bleeding occurs at the
implantation site as the
uterus is unable to contract
adequately and stop the flow
of blood from the open
vessels.

10. 10 03/23/12

11. * Muscles @ LS:
* relatively weaker layer of
muscle
* less blood supply, compared
to the upper segment.
* Caesarean operation is done
in the lower segment (across
the top of the pubic hairline)
* less likely to cause excessive
bleeding.

12. * The LUS is an important anatomical part of the
uterus
* It has anatomical and functional aspects that
can be utilized to produce a better outcome in
pregnancy and labour
* Attachment of the placenta to the LUS leads to
a risk of bleeding
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13. * Obstetrics by Ten Teachers
* http://www.pregnancy-labour.info/2009/04/changes-in-uteru
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