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The Anatomy of
Obstetrics
Kurt Kauffman, MD, FACOG
Objectives:
 Describe the muscular, neurologic and vascular anatomy
of the pelvis and vulva
 Describe the anatomic changes in the woman caused by
normal physiologic adaptation to pregnancy
 Describe the anatomic changes that occur during the
intrapartum period
 Describe the anatomic changes that occur during the
puerperium, such as alterations in the breast and
uterine involution
Pelvic anatomy - muscular
Pelvic blood supply
 Internal illiac artery
 Anterior branch
 Obturator artery
 Superior vesical artery
 Uterine artery
 Middle vesical artery
 Internal pudendal artery
 Posterior branch
 Illiolumbar artery
 Lateral sacral artery
 Anterior gluteal artery
Vulva
 Labia Majora
 Labia Minora
 Clitorus
 Vestibule
 Urethral meatus
 Vaginal introitus
 Perineum
Vulvar Cutaneous Innervation
Anatomic changes caused by
normal physiologic adaptation to
pregnancy
 Abdominal wall
 Pelvic organs
 Breasts
Rectus muscles
Pelvic organs
 Uterus enlarges to about 5 Liters total size (including all
contents (12 lbs)




Uterine muscle
Fetus
Placenta
Fluids
 Vagina lengthens
 Round ligaments lengthens
 Broad ligament stretches (venous plexus engorges)
Uterine size and gestational age
Pudendal Nerve
Controls:
External anal sphincter
External Urethral sphincter
Clitoral erection & Orgasm
Posterior perineum sensation
Vaginal/Labial changes with
pregnancy
 Increased vascularity
 Varicosities
 Unilateral or bilateral – may be quite tender
 May need supportive garment
 Enlargement
Breast Changes with Pregnancy
 After conception:
 Breast become swollen/tender
 Nipples are more sensitive/tingle
 Areola/nipple become darker by 12 weeks post conception
 Ductal, alveolar, and myoepithelial elements all undergo
marked hyperplasia. Ductal proliferation is
predominantly controlled by estrogen, but acinar
differentiation is a progesterone effect facilitated by
estrogen.
Pregnancy changes in the Breast
Anatomic changes during the
intrapartum period
 Dilation of the cervix
 Thinning/effacement
 Descent of the fetal head into the vagina
 Dilation of the vagina as the fetal head descends
 Dilation of the introitus/vulva as the baby crowns
 Separation of the placenta after the baby is delivered
 Lengthening of the cord, bleeding
 Injury/stretching of nerves to pelvis
 Perineum/bladder (Pudendal & vesical plexes/hypogastric)
Anatomic changes that occur
during the puerperium
 Involution (pelvic organs)
 Starts immediately post delivery of the placenta
 Lasts approximately 6 weeks
 Decrease in estrogen and progesterone aids in involution
 Breast Changes
Post partum involution
 Uterus starts immediate involution.
 Contractions immediately decrease blood flow which
decreased blood loss and helps with involution
 Uterine muscles atrophy quickly at first and then continue
for 6 weeks
 Uterus weighs around 900 grams immediately PP – but only
50 – 60 grams at 6 weeks PP
 Vagina also involutes, but slower
 Tubes, ligaments and vulvar muscles also involute and
return to near pre delivery size
Involution of Endometrium
 Endometrium necrosis and sloughs off
 Placental implantation site thrombosis over
 Basal layer is source of new endometrium
 Placental implantation site first shrinks in diameter,
then is exfoliated by undermining of site with new
endometrium
Involution of Vagina
 Slower to involute (takes 4 to 8 weeks)
 Regains tone, but never back to virginal state
 Mucosa remains delicate for few weeks
 Rugae partially reappear at 3rd week PP
 Introitus also remains larger than virginal state
Breast changes after delivery
 Mammary tissue becomes secretive with the abrupt
falling of estrogen and progesterone with delivery
 Lactogenesis requires 2-5 days (maturation of acinar
epithelium in breast)
 Once lactogenesis occurs completely, hormones
estrogen and progesterone have little effect on
production.
References
 Netter, F., Atlas of Human Anatomy
 Williams Obstetrics, 23rd edition
 Gabbe, G.G., et al, Obstetrics Normal and Problem
Pregnancies. Fourth edition.
 www.healthcare.phillips.com