physiological changes in uterus during pregnancy

  Uterus

Parts of uterus;

1. Body

2. Isthmus

3. Cervix

1. Changes in Body

Uterus                     Dimension Pregnant      Non-pregnant 

Weight of uterus     1000gm                         50gm

Thickness               0.6mm                            1.5mm

Length                    28-32cm                          7cm 

Width                     22-24cm                           4cm

Volume                 1500ml                            10ml

Changes in muscle;

1. Outer; longitudinal

2. Inner; circular

(Sphincter like arrangement around tubal orifices and internal OS.

3. Intermediate; thickest and strongest layer

Arranged in criss-cross (form 8), in between blood vessel run.

4. Hypertrophy and hyperplasia

Increase muscle size and enlargement of organ/tissue.

5. Stretching

Muscle fibres elongated (20 weeks) due to distension by growing fetus.

Uterine wall become thinner at term.

6. Softening of uterus

7. Vascular system

Blood supply; uterine artery, ovarian artery.

Uterine artery (20 weeks) diameter double increases, blood flow increases.

Vasodilation due to estrogen and progesterone.

Vein becomes dilated and valveless.

Numerous lymphatic channel open up.

Vericose vein; when valve not work properly.

Blood collect in legs and pressure builds up.

Valves (one way valves) inside vein help keep blood flowing in right direction.

8. Layers

Ectometrium

Myometrium

Endometrium; changes to decidua

9. Uterus shape

In non-pregnant woman; Pyriform

At 12 week pregnancy; Globular

At 28 week; Oval

At term (36 week); spherical

10. Position

Normal anteverted position.

Errect; 12 weeks

Term; anteverted

11. Contraction

Braxton-Hicks (contraction are irregular, infrequent, spasmodic and painless without any effect on dilatation of cervix.

During contraction complete closure of uterine vein with partial occlusion of artery, may cause diminished placental perfusion; cause transient hypoxia lead to fetal bradycardia.

11. Endometrium

Endometrium in non-pregnant women changes in decidua in pregnancy.

2. Isthmus

During first trimester isthmus hypertrophies.

Isthmus part found during pregnancy.

Elongation and formation of lower uterine segment (12 week).

3. Cervix

Hypertrophy

Hyperplasia

Goodell's sign; marked softening of cervix (6 week).

In non-pregnant woman cervix is hard.

Mucus plug formation; egg like mucus plug formation mixed with blood called show forms in cervical canal in early pregnancy to seal the cervix.

Show; tinged with blood

Operculum; mucus plug

Stroma in cervix;

Hypertrophy and hyperplasia of elastic and connective tissues, composed of fibromuscular collagen protein. Vascularity increased, bluish discoloration.

Increase progesterone breakdown of collagen fibres, cervix dilate and start labor process.