Anatomy & Physiology of Labor

Question 1

What are the major components of the pelvic floor?

Answer 1

1) endopelvic fascia
2) pelvic diaphragm
3) urogenital diaphragm
4) superficial perineal muscles

Question 2

What are the parts of levator ani muscle?

Answer 2

1) pubococcygeus
2) puborectalis
3) iliococcygeus

Question 3

What muscles surround the vagina?

Answer 3

bulbocavernosus

Question 4

Which muscles extend from the clitoris?

Answer 4

ischiocavernosus

Question 5

What is the function of the superficial/superior transverse perineal muscles?

Answer 5

fix the location of the central tendinous point to perineum

Question 6

What muscles attach to the central tendinous point of the perineum?

Answer 6

1) bulbocavernosus
2) superficial transverse perineal
3) some of deep transverse perineal
4) external anal sphincter
5) levator ani

Question 7

What nerve supplies cutaneous innervation of the perineum?

Answer 7

pudendal nerve

Question 8

What vessels supply and drain blood from the uterus?

Answer 8

arcuate vessels of uterus

Question 9

Where do the round ligaments insert?

Answer 9

from either side of uterus –> anterior portion of labia majora

Question 10

Which ligament connects sacrum to greater tuberosity of ischium?

Answer 10

sacrotuberous ligament

Question 11

What is the optimal distance between sacrum and ischial spines?

Answer 11

at least 2.5 fingerbreadths via sacrospinous ligament

Question 12

What is the optimal distance of the diagonal conjugate?

Answer 12

symphysis pubis to sacral promontory = at least 11.5cm

Question 13

What is the optimal measurement of the pelvic outlet?

Answer 13

• at least 11cm (>1 fist) from tuberosity to tuberosity

- at least 9.5-11.5cm from anterior to posterior

Question 14

What is the average biparietal diameter?

Answer 14

9.5-9.8cm

Question 15

What are the 4 types of pelvises?

Answer 15

1) gynecoid = round and wide
2) anthropoid = U-shaped symphysis pubis; oval-shaped from anterior to posterior; associated w/ OP
3) android = V-shaped symphysis pubis; heart-shaped; associated w/ male anatomy
4) platypelloid = narrow and oval-shaped transversely

Question 16

diagonal conjugate

Answer 16

from bottom of symphysis pubis to sacral promontory

Question 17

obstetric conjugate

Answer 17

from inside of symphysis pubis to middle of sacral promontory

= diagonal conjugate - 1.5cm

Question 18

transverse diameter of inlet

Answer 18

distance between ileopectineal lines

Question 19

interspinous diameter

Answer 19

distance betwen ischial spines

should be at least 10cm

Question 20

bituberous diameter

Answer 20

transverse diameter of outlet from tuberosity to tuberosity

Question 21

How do prostaglandins function in labor?

Answer 21

produced in myocytes –> stimulate nearby myocytes to depolarize –> contraction

Question 22

How do contractions facilitate labor?

Answer 22

fundal contraction –> progressively shorten uterine muscle fibers –> reduced uterine capacity –> descent of fetus towards more passive lower uterine segment

Question 23

Bandl’s ring

Answer 23

when active segment of uterus becomes so thick and shorter that a visible line is seen b/w active and passive segments of uterus

Question 24

descending gradient of fundal dominance

Answer 24

contractions. ..
1) start in fundus
2) last longer in fundus
3) progress from fundus to isthmus

Question 25

How do muscle bundles in the lower uterine segment respond to contractions?

Answer 25

becomes longer –> promotes fetal descent

Question 26

How does the uterus feel during contractions?

Answer 26

• upper segment is firm

- lower segment is softer, distended, and more passive

Question 27

contraction intensity

Answer 27

strength of contraction

Question 28

contraction frequency

Answer 28

beginning of one contraction to beginning of next

Question 29

contraction duration

Answer 29

beginning to end of one contraction

Question 30

calculate Montevideo units (MVU)

Answer 30

MVU = (amplitude - baseline resting tone) x frequency of UC in 10 min period

Question 31

What is considered adequate tone during a contraction?

Answer 31

• 200MVUs when subtracting baseline

- 240MVUs when baseline tone included

Question 32

What are signs of impending labor?

Answer 32

1) lightening/engagement = descent of fetus into true pelvis
2) cervical ripening, effacement, and dilation
3) passage of mucus plug
4) Braxton Hicks contractions
5) ROM
6) maternal perception of increased energy
7) GI distress - brief N/V/D, indigestion

Question 33

“true” labor

Answer 33

regular, painful contractions that promote cervical dilation

Question 34

What is the purpose of amniotic fluid during pregnancy?

Answer 34

• cushioning and fetal protection
• provides space for fetal movement and growth
• maintains consistent temperature and pressure
• promotes lung development

Question 35

What is the purpose of amniotic fluid in labor?

Answer 35

• fetal growth + amniotic fluid levels –> uterine stretching –> uterine activation
• hydrostatic action of fluid and membranes promotes cervical effacement and dilation
• PROM –> labor likely to begin w/in 33-107h

Question 36

How is the amnion involved in labor?

Answer 36

produces prostaglandins that can influence membrane rupture and uterine contractility

Question 37

What is the pH of amniotic fluid?

Answer 37

7.1-7.3

turns nitrazine paper blue

Question 38

fetal attitude

Answer 38

relation of fetal parts to each other, e.g. vertex, sinciput (aka military), brow, face

Question 39

fetal lie

Answer 39

relationship of long axis of fetus to long axis of parturient

Question 40

fetal presentation

Answer 40

part of fetus that presents first to maternal pelvis

Question 41

fetal position

Answer 41

relationship of denominator (i.e. occiput, sacrum, or mentum) to front, back, or sides of parturient pelvis (e.g. LOA, ROA, ROT, etc)