Lower uterine segment

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

1. NurFakhriyyah, LokemanHazli, Alia Nadhirah
Associate Professor Dr Hanifullah Khan
03/23/121

2. 03/23/122
*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

3. 03/23/123
*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

4. 03/23/124
*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

5. 03/23/125
*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).

6. 03/23/126

7. 03/23/127
*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.

9. *In such cases, the placenta is
attached partially or
completely to the LUS
*Placental a tta c hme nt
is d is rup te 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. 03/23/1210

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. 03/23/1212
*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

13. 03/23/1213
*Obstetrics by Ten Teachers
*http://www.pregnancy-labour.info/2009/04/changes-in-uterus-during-pregnancy.html